U.S. patent application number 12/013634 was filed with the patent office on 2008-06-19 for power converter.
This patent application is currently assigned to Progressive Dynamics, Inc.. Invention is credited to James C. Cook.
Application Number | 20080144341 12/013634 |
Document ID | / |
Family ID | 46205699 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080144341 |
Kind Code |
A1 |
Cook; James C. |
June 19, 2008 |
POWER CONVERTER
Abstract
A switch-type power converter includes a double FET switch
operating in a variable duty cycle mode under the control of a
Unitrode 3846 integrated circuit controller. Indications of excess
input voltage and reverse battery connections are provided by
circuits including an element which permanently changes state. A
cooling fan mounted on a finned heat sink is operated in a variable
speed mode.
Inventors: |
Cook; James C.; (Marshall,
MI) |
Correspondence
Address: |
YOUNG & BASILE, P.C.
3001 WEST BIG BEAVER ROAD, SUITE 624
TROY
MI
48084
US
|
Assignee: |
Progressive Dynamics, Inc.
Marshall
MI
|
Family ID: |
46205699 |
Appl. No.: |
12/013634 |
Filed: |
January 14, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11221962 |
Sep 8, 2005 |
|
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12013634 |
|
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60607950 |
Sep 8, 2004 |
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Current U.S.
Class: |
363/53 ; 318/634;
320/106; 336/200; 361/104 |
Current CPC
Class: |
H02M 1/32 20130101; H02M
3/28 20130101; Y10S 388/934 20130101 |
Class at
Publication: |
363/53 ; 361/104;
320/106; 336/200; 318/634 |
International
Class: |
H02H 7/125 20060101
H02H007/125; H02H 5/04 20060101 H02H005/04; H02J 7/00 20060101
H02J007/00; H01F 5/00 20060101 H01F005/00; G05D 23/275 20060101
G05D023/275 |
Claims
1. A power converter having an input for receiving a supply
voltage, a switch, and a duty cycle controller connected to control
the switch to regulate an output voltage produced by the converter
wherein the improvement comprises: a first circuit connected to
said input and responsive to a first level over-voltage condition
at said input for altering operation of duty cycle controller; and
a second circuit connected to said input and responsive to a second
level over-voltage condition at said input to irreversibly change
state without altering operation of the duty cycle controller.
2. A converter as described in claim 1 wherein the second level is
higher than the first level.
3. A power converter as described in claim 1 wherein the first
circuit comprises an amplifier, circuit connected to said input and
to a reference voltage, said amplifier circuit having an output
connected to said controller to shut, said controller down in
response to the first level over-voltage condition.
4. A power converter as described in claim 1 wherein the second
circuit comprises the series combination of a non-resettable fuse
and a Zener diode connected between said input and ground.
5. A power converter having an input connectible to an AC line
voltage source, a rectifier for converting an AC line voltage to
DC, a switching circuit comprising at least one power transistor, a
transformer having a primary side connected to said rectifier and
to said switch circuit and a secondary side connected to a
converter output, a controller circuit for operating said switch
circuit in a variable duty cycle mode wherein the improvement
comprises: a permanent over-voltage indicator circuit connected
between said rectifier and ground and including the series
combination of a voltage responsive semi-conductor device and an
element which irreversibly changes state in response to the
presence of an over-voltage condition at said rectifier output.
6. The power converter described in claim 5 wherein said element is
a fuse.
7. The power converter described in claim 5 wherein said
semi-conductor device is a Zener diode.
8. The power converter of claim 5 further comprising an
over-voltage shut-down circuit connected between said rectifier
output and said controller for shutting the controller down under
over-voltage conditions.
9. The power converter of claim 8 wherein said over-voltage
shut-down circuit further includes an operational amplifier.
10. A power converter comprising an input for receiving a supply
voltage, a switch including at least one power transistor, and a
duty cycle controller connected to cycle the switch on and off; an
over-voltage shut-down circuit connected between said input and
said controller and comprising an operational amplifier; said
operational amplifier having an output, connected to a shut down
pin of said controller to terminate cycling of the switch.
11. A power converter for charging a battery and having a switch, a
duty cycle controller connected to the switch, a transformer having
a primary side and a secondary side, an output inductor, the
primary side being connected to the switch and the secondary side
being connected to the output inductor, a circuit for indicating a
reverse battery connection and comprising a device connected
between the output inductor and ground and effective to
irreversibly change state when a reverse battery connection is
made.
12. A power converter as defined in claim 11 further including a
capacitor connected in parallel with said device.
13. A power converter as defined in claim 12 wherein the device is
a Schottky diode.
14. A power converter comprising a switch, a controller for
controlling the duty cycle of the switch, a transformer, an output
inductor and a converter output terminal; a circuit board having
conductive traces formed thereon, the inductor being mounted on the
current board such that at least one conductive trace runs from the
inductor to the output terminal; and a heavy gauge wire
conductively bonded to and along said one conductive trace.
15. A power converter comprising a switch, a controller for
controlling the duty cycle of the switch, a transformer, an output
inductor and a converter output terminal; a circuit board having
conductive traces formed thereon, at least one trace running from
the transformer to the output terminal; and a heavy gauge wire
conductively bonded to and along said one conductive trace.
16. A power converter including a switch, a controller for varying
the duty cycle of the switch, a heat sink for the switch, a fan for
causing the fan to cause air to flow over the heat sink; a heat
sensor; and a fan control circuit, the fan control circuit being
operative to control the supply voltage source to vary the speed of
the fan in response to increasing temperature of said sensor.
17. The power converter defined in claim 16 wherein the fan
comprises a motor mounted proximate the heat sink, the heat sink
comprises a metal extrusion having a recess machined into an end
thereof to provide an air gap between the heat sink and the fan
motor.
Description
RELATED APPLICATION
[0001] This application is a divisional of U.S. application Ser.
No. 11/221,962 filed under attorney docket no. PDY-112-A on Sep. 8,
2005, currently pending. The content of the U.S. patent Ser. No.
11/221,962 is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to power converters, and more
particularly to switch-type power converters designed for use in
recreational vehicles as a regulated power supply for DC load
devices and as a battery charger.
BACKGROUND OF THE INVENTION
[0003] As used herein, the terms "recreational vehicle" and "RV"
should be construed to embrace motor homes, trailers, campers, van
conversions, fifth wheels, boats, and similar products. The common
characteristic of these recreational vehicles is an electrical
system incorporating one or more batteries to provide power for DC
load devices, such as lights, refrigerators and motors. The more
sophisticated recreational vehicles may also have alternating
current systems and AC load devices such as stoves, televisions,
microwaves and heating and ventilating systems. The AC load devices
are typically powered, from, a 115 volt AC line voltage source
brought to the recreational vehicle through a power cord and plug.
Some recreational vehicles also carry generators powered by gas or
diesel engines and capable of producing as much as 20 or more
kilowatts of AC power.
[0004] It has become common to install power converters in
recreational vehicles. A typical power converter converts 115 vac
to 13.6 vdc and charges the RV battery or batteries as necessary.
It has become more and more common to use "switch type" power
converters rather than linear converters. There are numerous
reasons for this including a substantial weight savings. Switch
type power converters, often simply called "switchers" or
"switching" power converters, typically use one or two power
switching semi-conductor devices such as field effect transistors
("FET's") and a controller such as the Unitrode, UC 3846 for
operating the semi-conductor devices in a variable duty cycle mode.
Such devices further typically include a step-down transformer and
a smoothing circuit between the transformer and the regulated
output voltage terminal.
[0005] A designer of such converters faces numerous issues
including heat dissipation, noise generation, tolerance to unstable
or excessive supply voltages and protection of the expensive
circuit components found therein. The manufacturer of such devices
faces these and other issues including warranty claims based on
alleged defects when, in fact, field failures are often caused by
improper use such as (1) accidentally connecting the converter
input to an excessive voltage source such as a 220 vac line or an
improperly regulated or runaway generator; and (2) accidentally
connecting the RV battery in reverse polarity
[0006] Power converters which deal with some of these issues are
described in U.S. Pat. Nos. 5,600,550 and 5,687,066 issued to James
Cook in February and November, respectively, of 1997 and assigned
to Progressive Dynamics, Inc. of Marshall, Mich. The power
converter described in the '550 patent is of the switch type in
which the switch includes two FET's operating in a push/pull
fashion under the control of an integrated circuit controller such
as the Unitrode UC 3846. The converter further comprises a fan
powered by the converter output and a pair of thermistors mounted
on a large heat sink along with the FET's. One of the thermistors
is used in combination with a set-point device to turn the fan on
and off and the other is used to shut the controller down in the
event temperature reaches an extreme or intolerable level.
[0007] U.S. Pat. No. 5,687,066 describes a converter identical to
that of the '550 patent but adds overvoltage protection. This
feature is provided by a Zener diode to sense an overvoltage
condition in the dc output of a diode rectifier bridge used to
convert an ac line voltage to dc. If the rectified supply voltage
exceeds a predetermined limit, the Zener diode conducts and quickly
sends a signal to a shut down pin of the Unitrode controller to
prevent the controller from turning the FET's on. This protects the
FET's from damage until the overvoltage condition subsides.
SUMMARY OF THE INVENTION
[0008] The subject invention has for its foundation a switch-type
power converter/battery charger including a switch consisting of
one or more FET's operating in a variable duty cycle mode. An
integrated circuit controller such as the Unitrode UC 3846 is used
with appropriate feedback and a rectifier and LC filter in the
output stage to operate the switch to produce a regulated dc
output.
[0009] The subject converter in a typical commercial embodiment
includes a rectifier bridge so that the unit may be connected to a
standard 60 cycle normal 115 volt ac line. This is typical of the
line voltage made available by electric utility companies and/or
commercial generators. The feedback system is used to cause the
overall converter to operate in a current demand mode wherein the
duty cycle of the switch is adjusted to maintain the desired output
voltage.
[0010] In the preferred embodiment described herein, the converter
further comprises a transformer for stepping voltages within the
converter circuit down to a level suitable for use in connection
with dc load devices and the charging of conventional storage
batteries. Most of the reference voltages in the converter are
taken from the primary side of the transformer. In addition, the
fan supply and fan control are on the primary side of the
transformer. By supplying the fan from the primary side, an
undesirable drop in fan speed under heavy load conditions is
avoided.
[0011] According to a first, more specific aspect of the present
invention, a circuit is provided at or near the dc input of the
converter i.e., at or near the output of the ac-to-dc rectifier
circuit, for providing a permanent indication of an abnormal
over-voltage condition sufficient to cause circuit damage and
likely to be the result of operator error. In general, the
permanent over-voltage indicator comprises a circuit connected
between the output of the ac-to-dc rectifier and ground and
includes a device, such as a Zener diode, for establishing a very
high breakdown voltage, and a device, such as a fuse, which
permanently changes state in response to an over-current condition.
The fuse and Zener diode are preferably chosen in the commercial
embodiment to correspond to the conditions which might exist if the
converter were accidentally connected to a 220 volt ac supply or to
an unregulated or runaway generator. The permanent change of state
in itself has no effect on converter operation, since it is not a
shut down mechanism similar to that of the over-voltage protection
feature. But it does provide the manufacturer or warrantor of the
system with evidence that any damage occurring to the converter
and/or its various circuit components was the result of an extreme
over-voltage condition rather than system malfunction or component
defects.
[0012] The permanent input over-voltage indicator is preferably
used in combination with an over-voltage shutdown circuit also
connected to the output of the ac-to-dc rectifier. The location and
overall purpose of the over-voltage shutdown circuit is generally
as described in the '066 patent where it is referred to as an
overvoltage "protection" circuit, but preferably uses an
operational amplifier to establish the shutdown set point voltage
in a way which is more precise than that available from the use of
a Zener diode as described in the '066 patent. The output of the
over-voltage shutdown circuit is connected to a shut down pin in
the variable duty cycle controller so as to prevent the switch
transistors from turning on (and off again) while the over-voltage
condition persists. This protects the expensive FET's and other
components in the switch from damage. The set point of the
over-voltage shutdown circuit in the illustrated embodiment is
lower than that associated with the permanent, over-voltage
indicator device described above and the two circuits work in a
cooperative fashion; i.e., the over-voltage shutdown circuit
effects a shut down function at a first over voltage level whereas
the permanent over-voltage indicator circuit changes state at a
substantially higher over-voltage level likely resulting from, for
example, owner/user error or generator runaway. However, the trip
point of the overvoltage indicator could be set below or equal to
the overvoltage shutdown circuit if the circuit designer wishes to
do so.
[0013] Another aspect of the present invention in the foundation
environment described above is a permanent reverse battery
connection indicator circuit. This circuit detects a so-called
"reverse" battery condition which results from the erroneous
reverse polarity connection of the storage battery to the
recreational vehicle electrical system after a period of
disconnection for storage or service. Like the over-voltage
indicator, the permanent reverse battery connection circuit
includes a component which undergoes a permanent change of state
when the battery is accidentally connected with the positive and
negative terminals in reverse positions. Again, the permanent
indicator does nothing to shut down or disable system operation,
but simply provides an unequivocal indicator of owner/user error in
the event a warranty claim is later made.
[0014] The converter of the present invention, like the converter
described in the '066 patent, uses a metal heat sink as part of the
converter packaging structure and mounts certain components on or
in contact with the heat sink. A thermistor sensor, preferably
mounted on or in contact with the heat sink, is used to monitor
converter temperature and provide an output signal which; also
unlike the '066 patent converter, is simultaneously supplied to two
control circuits. The first control circuit operates the fan in a
variable speed mode. These modes of operation are believed to not
only extend fan life, but also reduce an annoying quality of fan
noise. The thermistor sensor also furnishes a temperature-related
signal to a second circuit including a comparator or "op-amp" to
shut down the variable duty cycle controller in the event of a high
temperature condition which may exceed the capacity of the fan.
[0015] Other aspects of the invention in the area of thermal
control include a special mounting arrangement between the fan
motor and the extrusion which provides the heat sink; i.e., a
recess is machined into an end of the heat sink extrusion to
provide an air gap between the extrusion and the fan motor so that
the fan motor does not directly pick up heat from the extrusion. In
addition, heavy wire leads are used in overlying relationship to
the copper plating of a circuit board used to mount the elements of
the circuit of FIG. 2. The wire leads are soldered to the board in
high current connector areas. Numerous advantages flow from these
packaging modifications as will be hereinafter explained in greater
detail.
[0016] Still further aspects and advantages of the invention are
described herein and will be best understood from a reading of the
following specification which describes and illustrative embodiment
in the form of an 80 amp power converter for use in recreational
vehicles of the type using conventional storage batteries.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a block diagram of a switched power converter
circuit according to the present invention;
[0018] FIG. 2 is a schematic circuit diagram of an illustrative
switched power converter circuit embodying the inventive features
described above;
[0019] FIG. 3 is a graph of temperature versus fan speed
illustrating the operating curve of the fan according to the
present invention;
[0020] FIG. 4 is a graph of fan voltage versus fan speed for a
typical fan;
[0021] FIG. 5 shows various waveforms within the circuit of FIG.
17;
[0022] FIG. 6 is a graph of output converter current versus
temperature for a variety of fan speeds;
[0023] FIG. 7 is a partial schematic diagram illustrating a
temperature-responsive input circuit according to the present
invention;
[0024] FIG. 8 is a graph of V.sub.tempvar of FIG. 7 versus fan
voltage showing the desired characteristic;
[0025] FIG. 9 shows partial schematics of a fan connected to an
operational amplifier;
[0026] FIG. 10 shows a partial schematic of a fan connected to an
open collector operational amplifier and a graph showing the
resulting fan voltage curve with temperature changes;
[0027] FIG. 11 shows the partial schematic of FIG. 10 with the
addition of a gain amplifier and a graph showing the resulting fan
voltage curve with temperature changes;
[0028] FIG. 12 shows the partial schematic of FIG. 11 with the
addition of circuit to shift the zero point of the fan voltage
curve and a graph showing the resulting fan voltage curve with
temperature changes;
[0029] FIG. 13 shows the equivalent circuit to the circuit to shift
the zero point of FIG. 12;
[0030] FIG. 14 shows the equivalent circuit to the open collector
operational amplifier of FIG. 12;
[0031] FIG. 15 is a schematic of a first embodiment of the control
circuit according to the present invention;
[0032] FIG. 16 is a schematic of a second, alternative, embodiment
of the control circuit according to the present invention;
[0033] FIG. 17 illustrates the two output current paths generated
by the secondary-output side of transformer T1;
[0034] FIG. 18 is a perspective view of a fully packaged power
converter embodying the features described herein;
[0035] FIG. 19 is a cross-section of an illustrative heat sink
showing a spring clip to hold a diode in the switch circuit against
the heat sink;
[0036] FIG. 20 is an end elevational view of the power converter
package of FIG. 18;
[0037] FIG. 21 is an opposite end elevational view of the power
converter package of FIG. 18;
[0038] FIG. 22 is a top plan view of the switched power converter
package of FIG. 18;
[0039] FIG. 23 is a perspective view of a RV partially broken away
to show the switched power converter according to the invention
positioned therein;
[0040] FIG. 24 is a perspective view of the heat sink of FIG. 19
showing a recess or relief in the fan mounting surface.
[0041] FIG. 25 is a photograph of one side of the circuit board
used to support the components in the circuit of FIG. 2 showing
heavy wires connected from the center top of the transformer
through the circuit board; and
[0042] FIG. 26 is a photograph of the reverse side of the circuit
board, with the image reversed to coincide with the orientation of
the FIG. 25 photograph, showing the heavy wires from the
transformer coming through the circuit board and soldered over the
conductive traces leading to the negative output terminal. This
photograph also shows additional heavy wires running from the fuses
to the positive output terminal and also soldered to and in
overlying relation to circuit board traces.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] FIG. 1 is a block diagram of a circuit for a switched power
converter embodying the features of the present invention. The
block diagram includes an AC-to-DC rectifier circuit 10, a switch
circuit 12, a transformer circuit 14, a feedback circuit 16, a
controller 18, an over-voltage shutdown circuit 20, a permanent
over-voltage indicator 22, a permanent reverse battery indicator
24, a thermistor circuit 26, a variable speed fan 32, fan control
circuit 30, an, over-temperature shutdown circuit 28, a current
sensing feedback circuit 34, a foldback circuit 42, and an output
rectifier and LC filter circuit 44 including the inductor L2
referred to hereinafter.
[0044] The AC-to-DC rectifier circuit 10 converts a 115v AC line
voltage into an unregulated and time-varying dc signal with an
average in the 170 volt range. It should be noted that the
converter 46 can be plugged into a 170vdc source, if available. In
this case the rectifier 10 performs no rectification functions. The
unregulated DC signal then enters the switching circuit 12 where
the on/off states and duty cycle of the switching circuit 12 is
determined by the controller 18 and feedback circuits 34 and 16.
The switching circuit 12 includes two field effect transistors
(FET's). The output of the switching circuit 12 is a regulated
waveform containing unidirectional pulses.
[0045] Current sensing feedback circuit 34 is connected to the
output of the switching circuit 12 for the purpose of measuring the
output current. The output of the current sensing circuit 34 is
connected to controller 18. Controller 18 adjusts the duty cycle of
the FET's in the switching circuit 12 according to the current
measured by the current sensing circuit 34 and the voltage measured
by circuit 16. Accordingly, duty cycle is controlled by two
factors: voltage feedback via circuit 16 and current feedback via
circuit 34.
[0046] Over-voltage shut-down circuit 20 is connected between the
output of the AC-to-DC rectifier circuit 10 and a shut-down pin of
the controller 18 for the purpose of shutting off the switching
circuit 12 in the event the rectified input voltage at 40 exceeds a
pre-determined threshold voltage such as 195 vdc. The permanent
over-voltage indicator 22 is connected to the output of the
AC-to-DC rectifier circuit 10 for the purpose of triggering a
permanent indicator in the event the voltage at 40 exceeds a
second, higher threshold voltage, such as 220 vdc. As noted above,
the second threshold voltage will typically be higher than the
first, but could be lower or equal to the first threshold voltage.
The over-voltage shut-down circuit 20 will protect the costly
transistor components of the switching circuit 12 from being
destroyed by the excessive input voltage conditions. The permanent
over-voltage indicator 22 will provide evidence to the manufacturer
that an undesirably high AC input voltage had been connected to the
converter, e.g., a 220 VAC line voltage. The threshold voltage
triggering the over-voltage shut-down circuit 20 is typically lower
than the threshold voltage triggering the permanent over-voltage
indicator 22, but can be higher or equal to the overvoltage
indicator circuit trigger voltage.
[0047] The regulated signal passes from the switching circuit 12 to
the transformer circuit 14. The transformer circuit 14 steps down
the average of the unidirectional pulses to the level necessary for
recreational vehicle use; e.g., ultimately to about 13.6 volts. The
stepped down waveform is rectified and smoothed by circuit 44
before application to load devices. Feedback circuit 16 measures
the voltage across the load. The output of the feedback circuit 16
is connected to controller 18. Controller 18 then controls the
on/off state and duty cycle of the switching circuit 12 based in
part on the input received from the feedback circuit 16.
[0048] A permanent reverse battery indicator 24 is also connected
across the DC load for the purpose of providing a physical record
that the operator connected a battery in reverse polarity. Such
reverse battery connections may cause damage to the switched power
converter, and the manufacturer may have an interest in knowing
whether the damage was caused by the reverse connection of the RV
battery as opposed to a manufacturing defect.
[0049] Thermistor circuit 26 senses the temperature of a heat sink
52 in the housing 70, and provides a variable resistance based on
temperature. Over-temperature shutdown circuit 28 receives a signal
from the thermistor circuit 26 and, if a set-point is exceeded,
sends a shutdown signal to the controller 18. Controller 18 then
terminates the operation of switching circuit 12. The
over-temperature shutdown circuit 28 will not permit the operation
of the switching circuit 12 until the temperature sensed by the
thermistor has fallen below the undesirable temperature limit.
Hysteresis in the circuit makes the temperature at which operation
is resumed lower than the shutdown temperature.
[0050] Fan control circuit 30 receives a signal from thermistor
circuit 26. The fan control circuit 30 produces a variable output
based on the input from the thermistor 26. A variable speed fan 32
is connected to the variable output signal of the fan control
circuit 30, such that the fan 32 will vary in speed based on the
input signal. Accordingly, the speed of the fan 32 increases in
response to increases in sensed temperatures. A low fan speed
minimizes the annoying effects of fan noise at low to moderate
power levels. The power supply for the fan 32 comes from the
primary side of transformer circuit 14. This feature eliminates the
tendency of the fan supply voltage to droop, with a corresponding
fan speed reduction, under heavy load conditions.
[0051] Having briefly described the overall block diagram of the
switched power converter circuit, the schematic circuit of an
illustrative, mechanical embodiment will be described in detail
with reference to FIGS. 2, 5 and 17. The preferred values of all
described electrical components are listed at the end of the
detailed description.
[0052] Input Circuit
[0053] Input circuit 36 is connected to a conventional AC power
supply through a cable having a conventional 3-prong connector. The
3-prong connector includes a ground conductor, a positive
conductor, and a neutral conductor. The cable runs into the housing
through an aperture 100. The AC positive terminal is connected to
AC positive input W1. The AC ground terminal is connected to AC
ground W2 identified by a "chassis ground" symbol. The AC neutral
terminal is connected to AC neutral input W3. AC positive input W1
is connected to thermistor RT2. Thermistor RT2 is used as an inrush
current protector for the purpose of protecting fully discharged
capacitors from receiving a surge of current. Thermistor RT2
initially (i.e. when cold) provides a high resistance but rapidly
changes to a substantially lower resistance as the temperature
increases, allowing an unrestricted AC signal to pass into the
noise suppression circuit 38. It should be noted that there is a
primary ground, secondary ground and a "chassis" ground and that
different symbols are used for these in FIG. 2.
[0054] Noise Suppression Circuit
[0055] The noise suppression circuit 38 includes capacitors C15,
C16, C26, C1, C2, C3, C30, C29, and C31, inductor beads L5, L6, L7,
and L8, jumpers J6, J7, J8, J9, J10, and J11, and common mode choke
(CMC) transformers T3, and T2. These electrical components provide
electromagnetic interference noise suppression, and filtering to
prevent noise from within the converter from traveling back into
the ac supply line. Noise transfer suppression is also provided by
capacitors C15, C16, and C26. One plate of C15 is connected to
thermistor RT2, and one plate of C16 is connected to AC neutral
input line W3. The other plates of capacitor C15, and C16 are
connected to chassis ground, i.e., the ground of input W2.
Capacitor C26 is connected in parallel to C15 and C16, where one
plate of capacitor C26 is connected to thermistor RT2, and the
other plate of capacitor C26 is connected to AC neutral input line
W3. Both plates of capacitor C26 are connected through CMC
transformer T3. Winding 2-1 of CMC transformer T3 is connected to
thermistor RT2, and winding 3-4 of CMC transformer T3 is connected
to AC neutral input line W3. The output of winding 2-1 is connected
to the input side of fuse F1.
[0056] Additional noise suppression is provided by capacitors C1,
C2, and C3. One plate of capacitor C1 is connected to the output
side of fuse F1, and the remaining plate of capacitor C1 is
connected to winding 3-4 of CMC transformer T3. Capacitor C1 is
also connected to one plate of each of capacitors C2 and C3. The
remaining plates of capacitors C2 and C3 are connected to chassis
ground. CMC transformer T2 is connected in parallel to capacitors
C2 and C3. Winding 2-1 of CMC transformer T2 is connected to the
ungrounded plate of capacitor C2, and winding 3-4 of CMC
transformer T2 is connected to the ungrounded plate of capacitor
C3. Jumpers J6, J7, J8, are connected in parallel to winding 2-1 of
CMC transformer T2, and jumpers J9, J10, and J11 are connected in
parallel to winding 4-3 of CMC transformer T2. All jumpers provide
the option of bypassing CMC transformer T2.
[0057] Additional noise suppression is provided by capacitors C30,
C29, and C31. The windings of CMC transformer T2 are connected in
parallel to capacitor C30. Capacitor C30 is also connected to one
plate of each of capacitors C29 and C31. The remaining plates of
capacitors C29 and C31 are connected, to chassis ground. High
frequency noise suppression is provided by inductor beads L5, L6,
L7, and L8. L6 and L8 are fitted onto the bridge connection wires
by causing the wires to pass through the center opening of each
inductor bead core, wrap around the bead core, and then pass again
through the bead core. The wires passing through L6 and L8 are then
connected between T2 and a diode bridge DB1 forming the AC-to-DC
rectifier 10. The inductor beads L5 and L7 are similarly mounted on
the wires coming out of the diode bridge DB1 (see FIG. 2).
[0058] AC-to-DC Rectifier
[0059] The AC-to-DC rectifier 10 is composed of a diode bridge DB1,
capacitors C4a, C4b, and C4c. The wires passing through L6 and L8
are connected to the input of diode bridge DB1. The wires passing
through L5 and L7 are connected to the output of diode bridge DB1.
Capacitors C4a, C4b, and C4c are connected in parallel between
wires passing through inductor beads L5 and L7. The wire passing
through L5 is connected to the positive plate of each capacitor
C4a, C4b, and C4c, and the wire passing through L7 is connected to
the negative plate of each capacitor C4a, C4b, and C4c. The
negative plates of capacitors C4a, C4b, and C4c are also connected
to ground. Under optimal conditions capacitors C4a, C4b, and C4c
are charged by the output of diode bridge DB1 to a desired voltage
of 170 volts. Capacitors C4a, C4b, and C4c provide an unregulated
DC signal to unregulated DC terminal 40.
[0060] Permanent Over-Voltage Indicator
[0061] The permanent over-voltage indicator 22 includes fuse Fx1
and Zener diode D23 connected in series between the output 40 of
rectifier bridge DB1 and ground. The permanent over-voltage
indicator 22 receives the voltage developed across capacitors C4a,
C4b, and C4c, and causes the fuse to change state if the voltage
across the capacitors reaches an undesirably high level. The
cathode of Zener diode D23 is connected to the output of fuse Fx1
and the anode of Zener diode D23 is connected to ground. It will be
noted in FIG. 2 there are three different ground symbols. One is
chassis ground, connected between C2 and C3 for instance. Another
is primary circuit ground, connected to pin 12 of U1 for instance.
And lastly there is a secondary circuit ground, connected to the
output P1 terminal for instance. Each of these three ground symbols
refer to separate voltage reference points and are isolated from
each other. It will be further noted that the primary ground symbol
is subdivided into an S, S2 and P ground. The explanation is:
[0062] S is the signal ground
[0063] S2 is the current sensing circuit ground
[0064] P is the power ground
In practice, these grounds are separate except at one point in
circuit board layout to avoid parasitic noise cross talk.
Nevertheless, physically they are the same since they are connected
by copper traces and wires. The same is the case for the S and P
shown with secondary ground symbol.
[0065] The purpose of the permanent over-voltage indicator 22 is to
provide a permanent indication of receiving an undesirably high
input voltage greater than that which triggers the over voltage
shut down circuit 20. If the permanent over-voltage indicator 22
changes state, it will be because the converter input receives an
excessive voltage, caused, for example, by a 220vac supply or
runaway generator. If enough voltage is applied to Zener diode D23
it will fail short creating a direct connection between fuse Fx1
and ground. This short failure of D23 causes Fx1 to permanently
change state, i.e., blow out to create an open circuit. The
preferred voltage limit of the permanent over-voltage indicator 22
is normally 220 volts dc. It will be noted that because the
indicator circuit 22 is a shunt, failing the diode and blowing the
fuse Fx1 does not disable the converter. The term "permanent" is
used herein to mean device which does not reset by itself, i.e., it
must be replaced to operate a second time. Since tripping the
indicator does not shut down the converter, the owner has no reason
to replace it and typically will not be aware of its presence.
Therefore, it remains in the converter until the converter is
returned for service or a warranty claim. For the majority of
converters, this never happens. However, for the small percentage
of converters returned for a warranty claim, the indicator helps
the manufacturer evaluate the likelihood that circuit failures are
the result of excessive input voltage other than manufacturing or
material defect. If a converter is returned for service and the
indicator fuse Fx1 is failed, it will be replaced along with any
other failed components and may, for example, signal the need to
provide the owner with a cautionary message regarding the quality
of the supply voltage source being used.
[0066] Over-Temperature Shut-Down Circuit
[0067] The over-temperature shutdown circuit 28 measures the heat
sink temperature in the switched power converter and triggers a
shutdown of the switching circuit 12 upon receiving an undesirably
high temperature. The over-temperature shutdown circuit 28 includes
Schottky diode D3, resistors R8, RN1B, R7, and RN1A, operational
amplifier U3A, and thermistor RT1. Thermistor RT1 changes in
resistance based on sensed temperature. Preferably thermistor RT1
is a negative-temperature-coefficient device and is mounted on or
in contact with the converter heat sink 52 in the manner shown in
FIG. 19; i.e., a spring clip holds the sensor against a surface of
the casting which makes up the sink 52. Because the FET's in the
switch 12 are also mounted in contact with the sink 52, heavier
load conditions cause the temperature of the sink 52 to rise. If
turning the fan 32 on stabilizes the temperature, no further remedy
is needed. It should be noted that the thermistor RT1 does not have
to be mounted on the heat sink, but can be mounted to measure, for
example, air temperature or the temperature of some component such
as the transformer 14 or the output inductor in circuit 44. The
illustrated arrangement is, however, preferred.
[0068] Operational amplifier U3A is used as a comparator for the
purpose of triggering shutdown pin (pin 16) of controller 18 in the
event that the internal temperature of the switched power converter
exceeds a set-point temperature. Once shutdown pin (pin 16) of
controller 18 is triggered the operation of switching circuit 12 is
terminated.
[0069] Operational amplifier U3A includes the following
connections: pin 1 is the output, pin 2 is the negative input, pin
3 is the positive input, pin 4 is connected to a 5 volt reference
voltage 5REF, and pin 11 is connected to ground. Pin 2 is connected
to a temperature based variable voltage coming from a voltage
divider circuit comprised of resistor RN1A and thermistor RT1. Pin
3 is connected to a reference voltage through a voltage divider
circuit using resistors R8, R7, and RN1B. Pin 1 is connected to
resistor R8, and Schottky diode D3 leading to shutdown pin (pin 16)
of controller 18.
[0070] The output of operational amplifier U3A will remain at a low
(ideally zero) voltage and will not trigger shutdown pin 16 of
controller 18 as long as pin 3 input does not exceed the pin 2
input. When the internal temperature is sufficiently high, the
voltage on pin 3 will exceed the voltage on pin 2 and the output of
pin 1 will go high and trigger a shutdown.
[0071] The over-temperature shutdown circuit 28 will operate as
follows under a cold temperature condition (i.e. a temperature
condition where a thermal shutdown is not required). Resistor RN1A
and thermistor RT1 form a voltage divider circuit. Resistor RN1A is
connected to a 5 volt reference 5REF and thermistor RT1 is
connected to ground. Thus, pin 2 receives the voltage between
resistor RN1A and thermistor RT1. Accordingly, the voltage applied
to pin 2 will vary depending on the temperature of the heat sink
52.
[0072] The value of resistor RN1A is 16.2K ohms, and the value of
thermistor RT1 is 100K ohms of 25.degree. C. Thus, when the
switched power converter is initially turned on and the temperature
is cold the value of thermistor RT1 will be about 100K ohms. At
cold startup the voltage applied to the pin 2 of operational
amplifier is roughly 4.3 volts. Further, at a cold (i.e. non
thermal shutdown) temperature pin 1 will be near 0 volts because
the voltage at pin 2 is higher than the voltage at pin 3. When the
voltage at pin 1 is near 0 volts, resistor R8 is parallel with
resistor R7.
[0073] In the illustrative embodiment, the values of resistors R8,
R7 and RN1B are 499K, 32.4K, and 47.5K ohms respectively. Because
resistors R8 and R7 are in parallel, their equivalent resistance at
25.degree. C. is 30.4K ohms. This resistance of 30.4K ohms will be
called R.sub.coldtemp. Accordingly, the voltage at pin 3 will be
the measured voltage between resistor RN1B and R.sub.coldtemp.
Using a voltage divider, the voltage applied to pin 3 at a cold
temperature is 1.925 volts. This voltage will be called
V.sub.coldtemp. Accordingly, at a cold temperature the voltage at
pin 3 will be V.sub.coldtemp which is 1.925 volts. If the internal
temperature significantly increases, the resistance of thermistor
RT1 will decrease and the voltage applied to pin 2 will fall below
the voltage applied to pin 3, the output of pin 1 will become
positive, and the switched power converter will experience a
thermal shutdown.
[0074] The over-temperature shutdown circuit 28 will operate as
follows under a thermal shutdown condition (i.e. a temperature
condition where an over-temperature shutdown is required). A shut
down temperature is never reached if the load on the converter is
within normal specifications because the fan 32 will provide
sufficient cooling. If the load is very heavy and/or the operator
has covered the converter 46 with blankets or the like, a shut down
temperature may be reached. If this happens, the voltage applied to
pin 1 will be approximately 5 volts. When pin 1 reaches 5 volts,
resistors RN1B and R8 will be in parallel (as opposed to resistor
R7 being in parallel with resistor R8 at a cold temperature). The
equivalent resistance of resistors RN1B and R8 in parallel is
43.37K ohms. This resistance will be called R.sub.hottemp.
Accordingly, the voltage at pin 3 will be the measured voltage
between resistor R7 and R.sub.hottemp. Using a voltage divider the
voltage applied to pin 3 at a cold temperature is 2.138 volts. This
voltage will be called V.sub.hottemp. Accordingly, in order for the
switching circuit 12 to begin operation the voltage on pin 2 must
rise above V.sub.hottemp (rather than V.sub.coldtemp). This
hysteresis caused by resistor R8 is important so that the switching
circuit 12 will not be enabled until the internal temperature falls
significantly below the temperature at which the thermal shutdown
was triggered.
[0075] Over-Voltage Shutdown Circuit
[0076] The over-voltage shutdown circuit 20 measures the voltage of
capacitors C4a, C4b, and C4c, and will shutdown the switching
circuit 12 in the event of an over-voltage condition at point 40.
The over-voltage circuit 20 includes resistors R38, R39, R40, R7,
and RN1B, operational amplifier U3B, and Schottky diode D27. The
output of over-voltage shut down circuit 20 is connected to
shutdown pin 16 of controller 18, such that a high signal will
terminate the operation of switch 12. The over-voltage shut-down
circuit 20 assures that transistors Q2a and Q2b are not damaged in
the event of an undesirably high voltage at the output of the
ac-to-dc converter; i.e., at point 40. As discussed above, there
are a number of factors which may cause high voltage conditions to
exist. Lightning strikes or transients from other loads on the
supply line, unregulated generators, runaway generators and the
like may all cause over-voltage conditions.
[0077] Transistors Q2a and Q2b are rated at 500 volts. Because of
the properties of transformer T1, transistor elements Q2a and Q2b
will experience a voltage twice that imposed on capacitors C4a,
C4b, and C4c. Accordingly, when capacitors C4a, C4b, and C4c are at
250 volts, the transistor elements Q2a and Q2b will experience 500
volts. Accordingly, if the voltage of capacitors C4a, C4b, and C4c
exceeds 250 volts transistors Q2a and Q2b may be damaged.
[0078] Operational amplifier U3B includes the following
connections: pin 7 is the output, pin 6 is the negative input, pin
5 is the positive input, pin 4 is connected to a 5 volt reference
voltage 5REF, and pin 11 is connected to ground. Pin 5 is connected
to a voltage divider circuit comprised of resistors R38, R39, and
R40. The voltage applied to pin 5 will vary depending on the line
voltage of capacitors C4a, C4b, and C4c. Pin 6 is connected to a
reference voltage through a voltage divider circuit comprised of
resistors R8, R7 and RN1B. Pin 7 is connected to resistor R40, and
schottky diode D27 leading to shutdown pin 16 of controller 18. The
output of operational amplifier U3B will remain as a low, ideally
zero, voltage and will not trigger shutdown via pin 16 of
controller 18 as long as pin 5 input does not exceed pin 6 input.
When the line voltage of capacitors C4a, C4b, and C4c is
sufficiently high, the voltage on pin 5 will exceed the voltage on
pin 6 and the output of pin 7 will trigger a shutdown.
[0079] The over-voltage shut-down circuit 20 will operate as
follows under a normal voltage condition (i.e. a voltage condition
that does not require an over-voltage shutdown). Resistors RN1B and
R7 form a voltage divider circuit, where resistor RN1B is connected
to a 5 volt reference 5REF and resistor R7 is connected to ground.
Accordingly, pin 6 receives the voltage between resistor RN1B and
R7. Remember, that the voltage applied between resistors RN1B and
R7 will vary depending upon the operation of the over-temperature
circuit 28 (i.e. when the temperature is cold resistor R8 is in
parallel with resistor R7, and when a thermal shutdown temperature
is achieved resistor R8 is in parallel with resistor RB1B).
Accordingly, the voltage applied to pin 6 will vary depending on
whether or not a thermal shutdown temperature is present. However,
once a thermal shutdown has been triggered by over-temperature
shut-down circuit 28 the operation of the over-voltage circuit 20
is irrelevant. Thus, for this explanation it will be assumed that
the temperature is below shutdown level and resistor R8 is in
parallel with resistor R7.
[0080] In the illustrated embodiment, the values of resistors R8,
R7 and RN1B are 499K, 32.4K, and 47.5K ohms respectively.
Remembering that at a low temperature resistors R8 and R7 are in
parallel, their equivalent resistance is 30.4K ohms. This
resistance of 30.4K ohms will be called R.sub.coldtemp.
Accordingly, the voltage at pin 6 will be the measured voltage
between resistor RN1B and R.sub.coldtemp. Using a voltage divider
the voltage applied to pin 6 at a cold temperature is 1.925 volts.
This voltage will be called V.sub.shutdownref.
[0081] In illustrative embodiment, the value of resistors R38, R39,
and R40 is 84.5K, 866, and 97.6K ohms, respectively. Prior to an
over-voltage shutdown, pin 7 will remain at a low, ideally zero,
voltage, causing resistor R40 to be in parallel with resistor R39.
The equivalent resistance of resistors R39 and R40 in parallel is
858.4 ohms. This resistance of 858.4 ohms will be called
R.sub.normalvoltage. Pin 5 receives the voltage between the voltage
divider circuit created by resistors R38 and R.sub.normalvoltage.
Accordingly, the unregulated DC terminal 40 voltage must exceed 195
volts for the voltage at pin 5 to exceed V.sub.shutdownref (e.g.,
if unregulated DC terminal 40 carries a voltage of 195 volts, pin 5
will be at approximately 1.961 volts which sufficiently exceeds the
1.952 volts applied to pin 6). Thus, when the unregulated DC
terminal 40 reaches a voltage of 195 volts the output, of pin 7
will become positive causing controller 18 to shutdown the
switching circuit 12. Because capacitor voltage is approximately
1.4 times AC line voltage, the illustrative embodiment of the
over-voltage shutdown circuit 20 will shut down the DC output if
the AC input voltage exceeds 140 volts (i.e. the voltage of
capacitors C4a, C4b, C4c exceeds 195 volts). Remember that the
preferred embodiment of the permanent over-voltage indicator 22
will be triggered at about 220 volts. Accordingly, the output of
the switched power converter will be terminated by the over-voltage
shut down circuit 20 at a lower over-voltage condition than that
which changes the state of the fuse Fx1 in the permanent
over-voltage indicator 22.
[0082] The over-voltage shutdown circuit 20 operates as follows
under an over-voltage shutdown condition (i.e. the AC input voltage
exceeds 140 volts). When a over-voltage shutdown condition is
reached, the voltage applied to pin 7 is approximately 5 volts.
When, pin 7 reaches 5 volts, resistor R40 is no longer in parallel
with resistor R39, but will be used for a hysteresis effect. For
example, when pin 7 is positive (i.e. over-voltage condition)
resistor R40 will provide feedback into pin 5, which will in turn
increase the voltage at pin 5. Accordingly, once operational
amplifier U3B triggers a shut down, the voltage at terminal 40 must
be significantly lower than the 195 volts which triggered the
initial shut down because resistor R40 has temporarily increased
the voltage measured by pin 5. The purpose of the resistor R40
hysteresis is to prevent the controller 18 from operating the
switching circuit 12 until the voltage at terminal 40 has
significantly fell below 195 volts.
[0083] Fan control Circuit
[0084] The fan control circuit 30 includes resistors RN1A, R4,
RN1C, R2a, R1, and R20, thermistor RT1, operational amplifier U3D,
transistor Q1, capacitor C5, and Schottky Diode D1a. FIGS. 2-16 are
used to describe the operation of the fan control circuit 30 and
the fan 32. In this embodiment, the fan 32 is powered by a dc motor
which varies in speed as a function of voltage amplitude; i.e., it
is the control circuit which produces the variable speed
characteristic. The fan control circuit 30 commands the fan 32 to
come on at an initial (lowest) temperature. The speed of the fan 32
increases with temperature and will maximize at some point prior to
the switched power converter being at full load. The fan control
circuit is also described in the aforementioned provisional
application, attorney docket no. PDY-106-A, the content of which is
incorporated herein by reference.
[0085] An operating curve of the fan 32 using the fan control
circuit 30 is shown in FIG. 3. (The slope is not necessarily linear
as discussed in more detail herein.) The fan control circuit 30
will cause the fan 32 to come on at low speed when temperatures are
over the set point by only a small amount.
[0086] The relationship between the voltage applied to the fan and
the fan speed is shown in FIG. 4. Due to static friction the fan 32
does not start moving until a certain voltage is reached.
Specifically, and as illustrated in FIG. 4, the fan blades will not
move until the voltage at point 2 is reached. Compared to the
thermal time constants, it more or less instantaneously starts
moving, jumping to point 3 (initial turn on point). As the voltage
increases, it moves to point 4, where the fan 32 is operating at
maximum speed. On the way down, the variable voltage controlled fan
32 follows from point 4 (maximum operation) to point 3 (initial
turn on point) to point 1 (shut off).
[0087] FIG. 6 illustrates in principle how the fan control circuit
30 works. Temperatures T.sub.H and T.sub.L are the temperatures at
which the fan 32 is ideally full on and full off, respectively.
More accurately, T.sub.H (line C) is the temperature at which full
fan voltage is applied, and T.sub.L (line D) is the temperature at
which no voltage is applied to the fan 32. Currents below point 14
have steady-state operating points on the "fan off" line (line B).
currents above point 15 have steady-state operating points on the
"fan full on" line (line A). Therefore, points 14 and 15 must be
the beginning and end of the line of operating points when
operating at currents where the variable voltage controlled fan 32
is in an intermediate state between full on and full off. Although
a straight line (line E) is shown connecting these two points, the
relationship is not necessarily a linear one. It is clearly,
however, a strictly increasing (positive slope) function. FIG. 6
illustrates the ideal case.
[0088] Assume the switched power converter starts cold at current
operating point I.sub.OP2, point 1. The switched power converter
will warm up and at point 2, T.sub.L, the fan 32 will start to turn
slowly. The heat sink 52 continues to warm up until it reaches its
steady-state operating point, point 4. Similarly, for current
operating point I.sub.OP1, the switched power converter will start
at point 18, the fan 32 will come on at point 6 and settle into a
steady speed at point 7.
[0089] Turning to FIG. 4, the operating characteristics of fan 32
are explained. Assume that T.sub.L1 corresponds to point 1 on FIG.
4 and that T.sub.L2 corresponds to point 2 on FIG. 4 (same as point
3). Thus, returning to FIG. 6, line G describes an actual fan 32.
Again, this relationship is not necessarily a linear one as shown,
but it is a positive slope function. Starting cold with operating
current I.sub.OP2, the temperature increases. At point 2 (T.sub.L),
voltage starts being applied to the variable voltage controlled fan
32, but it is not yet moving. At point 3 (T.sub.L2) the fan 32
begins to rotate. The switched power converter continues to heat up
and eventually settles at point 5 (along line G). For I.sub.OP1,
the switched power converter would start cold at point 18 and heat
up to point 6 (T.sub.L). At point 6, voltage begins to be applied
to the fan 32. The switched power converter will continue to heat
up until point 9 (T.sub.L2), where the fan 32 begins moving. The
fan 32 will now be moving faster than it needs to, the switched
power converter will cool and eventually settle into a steady state
speed at point 8 (along line G).
[0090] In both cases, the fan 32, once started, continues to
rotate. There is no discontinuance of operation. Notice further
that variable voltage controlled fan 32 speeds are slower (and less
noisy) for all current levels up to point 15 (T.sub.H). Also notice
the minimum current to turn the fan 32 on corresponds to point 17
(T.sub.L2), but if already on, it will stay on to a lower current,
corresponding to point 16 (T.sub.L1).
[0091] A description of the fan control circuit 30 is illustrated
in FIGS. 2, and 7-16. The preferred embodiment of the fan control
circuit includes resistors RN1A, R4, RN1C, R1, and R2a, thermistor
RT1, transistor Q1, and operational amplifier U3D. Operational
amplifier U3D includes the following connections: pin 14 is the
output, pin 12 is the positive input, pin 13 is the negative input,
pin 11 is connected to ground, and pin 4 is connected to a 5 volt
reference voltage 5REF.
[0092] As illustrated in FIGS. 2, and 7, thermistor RT1 is used as
a temperature sensor for the fan control circuit 30 as well as the
over-temperature shutdown circuit 28. Thermistor RT1 is connected
to ground as well as resistor RN1A which also connected to a 5 volt
reference 5REF. Thermistor RT1 and resistor RN1A are used to create
a voltage divider circuit where V.sub.tempvar is the output of the
voltage divider circuit. V.sub.tempvar is connected to pin 13 of
operational amplifier U3D. Preferably RT1 is a
negative-temperature-coefficient thermistor. As the internal
temperature increases, V.sub.tempvar decreases. For the remainder
of the fan control circuit 30, a profile of a desirable fan voltage
versus V.sub.tempvar is shown in FIG. 8.
[0093] Because the components used in switched power converter
(i.e. operational amplifier U3D) are powered by 5 volts, whereas
the fan 32 requires a nominal 12 volts, a direct connection of an
operational amplifier such as that shown in FIG. 9 will not work.
Simply stated an operational amplifier such as operational
amplifier U3D cannot supply sufficient current or voltage to the
fan 32. Neither will transistor emitter follower-type circuits work
because of voltage limitations. An open collector operational
amplifier would work in a circuit such as that shown in FIG. 10,
and a simple gain amplifier would almost provide the desired
profile as shown in FIG. 11. Shifting the "zero" point will get the
desired profile as shown in FIG. 12. Specifically, a Thevenin
resistance and voltage coupled to the negative input of the
operational amplifier would shift the zero point of the fan
control.
[0094] FIG. 13 illustrates an equivalent of the Thevenin resistance
and voltage, and the open collector operational amplifier is shown
equivalently in FIG. 14. Using a conventional operational amplifier
having an output connected to resistor R1 and transistor Q1 will
result in a complete fan control circuit according to FIG. 15. In
almost all cases, the fan 32 will be quiet, and only under extended
high load or high ambient temperature condition will the switched
power converter warm up enough to cause the fan 32 to be heard.
[0095] Because the circuit in FIG. 15 has a linear range between
full on and full off, significant power will be dissipated in
transistor Q1 at intermediate fan speeds. An alternative is to
modify the linear circuit to act as a duty cycle control circuit as
shown in FIG. 16. With duty cycle control, transistor Q1 will be
either full on or full off (zero voltage or zero current), but the
duty cycle will vary to control the speed of the fan.
[0096] In FIG. 16, resistor R3 adds hysteresis and causes
operational amplifier U3D to behave as a comparator. As the
switched power converter warms up, transistor Q1 is off until it
reaches a "low" temperature. The fan control circuit 30 then breaks
into oscillation with low "on" duty cycle on transistor Q1. As the
switched power converter continues to warm, the duty cycle gets
larger. When an upper temperature is reached, the oscillation
stops, and transistor Q1 is always on and stays on as the
temperature increases further.
[0097] The fan control circuit 32 as shown in FIG. 2 includes
resistors RN1C and R4 acting as a voltage divider circuit connected
to pin 12 of operational amplifier U3D. Resistor RN1C is connected
to 5 volt reference 5REF and resistor R4 is connected to ground.
The preferred value of resistor RN1C is 9.53K ohms, and the
preferred value of resistor R4 is 22.6K ohms. More exactly, the
currents flowing through R2a will also contribute to voltage at pin
12. Analysis yields
VP 1 N 12 = + 5 VREF RNIC + VQ 1 C R 2 a 1 R 2 a + 1 RNIC + 1 R 4
##EQU00001##
where R2a has the preferred value of 453K and VQ1C is the collector
voltage of Q1. When Q1 is off and no current flows through the fan,
VQ1C can be as high as the voltage in C5, which can vary with line
voltage.
[0098] Using a nominal value of 15 volts for the voltage on C5
yields pin 12 voltages;
[0099] VPIN12=3.4657 for VQ1c=0 volts
[0100] VPIN12=3.6844 for VQ1c=15 volts
[0101] Thus VPIN12 can more exactly have a range of voltages
between 3.4657 and'3.6844 depending on the voltage at the collector
of Q1. At pin 13 of operational amplifier U3D, resistor RN2A and
thermistor RT1 act as a voltage divider circuit. The preferred
value of resistor RN1A is 16.2K ohms, and the preferred value of
thermistor RT1 is 100K ohms at a cold start up temperature
(25.degree. C.). Accordingly, the initial voltage applied to pin 13
at a cold temperature is approximately 4.3 volts, which will be
called V.sub.tempvar.
[0102] At the initial startup of the switched power converter 46,
V.sub.tempvar is greater than 3.68v. Thus the output of operational
amplifier U3D is near zero causing transistor Q1 to be off and the
fan 32 is not running. As the temperature increases, the resistance
of thermistor RT1 will decrease causing the value of V.sub.tempvar
to drop from the initial 4.3 volts. Eventually the temperature will
increase such that the value of V.sub.tempvar will fall slightly
below 3.68 volts. When this occurs, the circuit including
operational amplifier U3D will enter the linear region. There will
be a slight fan voltage but it will probably remain in the stalled
condition. If the temperature continues to increase the value of
V.sub.tempvar will fall significantly below 3.68v but above 3.46v
and operational amplifier U3D causes the fan to enter the mid speed
range. As V.sub.tempvar falls further, op-amp U3D turns transistor
Q1 full on and the fan 32 reaches full speed.
[0103] The fan control circuit 30 provides the variable voltage to
control the speed of the fan 32. The transformer circuit 14
provides steady power to the power input of the fan 32. The power
input for the fan 32 is connected to pin 3 of transformer T1,
through Schottky diode D1a and resistor R20. Pin 7 of transformer
T1 is connected to ground, completing the power input circuit for
the fan 32. Resistor R20 is used for the purpose of preventing the
voltage applied to the fan 32 from exceeding specifications. One
plate of capacitor C5 is connected to ground and the other plate is
connected between resistor R20 and Schottky diode D1a for the
purpose of providing a steady voltage to resistor R20. Capacitor C5
is charged by transformer T1 and carries enough voltage to power
the fan 32. Schottky diode D1a prevents capacitor C5 from
discharging into pin 3 of transformer T1.
[0104] Because the power input to the fan 32 is connected to the
primary side of the transformer circuit 14, the fan control circuit
30 as well as the variable voltage controlled fan 32 will remain
operational even when the output is heavily loaded or short
circuited. Simply stated, this feature will permit the cooling
system of the switched power converter to continue to operate in
the event of an over-loaded output. Appropriately, the occurrence
of this condition is when the operation of the fan 30 is most
vital.
Transformer Circuit
[0105] Transformer circuit 14 is primarily inclusive of transformer
T1. Pin 4 of transformer T1 is the positive input fine. Pin 4 is
connected to unregulated DC terminal 40, where the DC line voltage
is approximately 170 volts. Pins 5 and 6 of transformer T1 are
connected to the switching circuit 12. The switching circuit 12
provides a switching current to the primary-input side of
transformer T1. For example, switching circuit 12, which is
controlled by controller 18, allows current to flow between pins 4
and 5, and between pins 4 and 6. However, the current between pins
4 and 5, and pins 4 and 6 will never flow simultaneously, but will
alternate according to controller 18. Operation is described below
with reference to FIG. 17.
Switching Circuit
[0106] As illustrated by FIGS. 2 and 17, the preferred embodiment
of the switching circuit 12 contains two transistors Q2a and Q2b.
When transistor Q2a is turned on current I.sub.1 will flow from pin
4 of transformer T2 to pin 6. Alternatively when transistor Q2b is
turned on current I.sub.2 will flow from pin 4 of transformer T1 to
pin 5. When transistor Q2a is on transistor Q2b will be off, and
when transistor Q2b is on, Q2a will be turned off. The
primary-input side of transformer T1 is utilized in such a fashion
so that the transistors within the switching circuit 12 may operate
at up to a maximum 50% duty cycle, meaning that, transistors Q2a
and Q2b are never on more than 50% of the time.
[0107] As further illustrated in FIGS. 2 and 17, the
secondary-output side of transformer T1 includes pins 2, 8, and 1.
When current I.sub.2 flows between pins 4 and 5 of transformer T1,
current I.sub.4 will correspondingly flow between pins 8 and 2.
Alternatively, when current I.sub.1 flows between pins 4 and 6 of
the primary-input side of transformer T1, current I.sub.3 will
correspondingly flow between pins 8 and 1 of the secondary-output
side. The switching circuit 12 further includes R37, R23a, R23b and
C24 (shown only in FIG. 2).
[0108] Transistors Q2a and Q2b provide two current loops.
Transistor Q2a is connected to pin 6 on the primary side of
transformer T1, and transistor Q2b is connected to pin 5 on the
primary side of transformer T1. Controller 18 controls the on/off
state of transistors Q2a and Q2b. When transistor Q2a is turned on,
Q2b is off. Current I.sub.1 flows between pins 4 and 6 of
transformer T1; alternatively, when transistor Q2b is turned on,
Q2a is off and current I.sub.2 flows between pins 4 and 5 of
transformer T1. The gate of transistor Q2a is connected to resistor
R23a which is connected to AOUT (pin 11) on controller 18. The gate
of transistor Q2b is connected to resistor R23b which is connected
to BOUT (pin 14) on controller 18. When controller 18 applies a
voltage to the gate of transistor Q2a, transistor Q2a turns on and
allow current I.sub.1 to flow from pin 4 of transformer T1, through
pin 6, and then to ground through the drain and source of
transistor Q2a. Alternatively, when controller 18 applies a voltage
to the gate of transistor Q2b, transistor Q2b will turn on and
allow current I.sub.2 to flow from pin 4 of transformer T1, through
pin 5 and to ground through the drain and source of transistor Q2b
.
[0109] Resistor R37 and capacitor C24 are connected in series
between the drain of transistors Q2a and Q2b for the purpose of
snubbing the transient drain voltage when transistors Q2a and Q2b
are switching.
Controller
[0110] Controller 18 is used for controlling the output of the
switching circuit, 12 by controlling the duty cycles of switching
transistors Q2a and Q2b. Controller 18 receives input from the
current sensing circuit 34, over-voltage shut-down circuit 20,
over-temperature shut-down circuit 28, feedback circuit 16, and
foldback circuit 42.
[0111] As discussed previously, AOUT (pin 11) and BOUT (pin 14) are
connected to transistors Q2a and Q2b respectively for the purpose
of controlling the duty cycle and switching current of the
switching circuit 12. SHDN (pin 16) is connected to both the output
of the over-voltage shutdown circuit 20 and the over-temperature
shutdown circuit 28 for the purpose of terminating the operation of
the switching circuit 12. If SHDN (pin 16) receives a sufficient
voltage AOUT (pin 11) and BOUT (pin 14) will turn off transistors
Q2a and Q2b, which will terminate the output across the DC
load.
[0112] CS+ and CS- are connections to operational amplifier CS,
which is internal to controller 18. The output of operational
amplifier CS corresponds to the instantaneous voltage output of
current sensing circuit 34. CS+ (pin 4) is connected to the output
of the current sensing circuit 34, which measures the. current
through transistors Q2a and Q2b.
[0113] EA+, EA-, and COMP are connections on operational amplifier
EA, which is internal to controller 18. The output of operational
amplifier EA is compared to the output of operational amplifier CS.
EA+ (pin 5), is connected to the output of the feedback circuit 16.
EA- (pin 6) is connected to COMP (pin 7), acting as a voltage
follower on operational amplifier EA. Accordingly, the output of
operational amplifier EA will be the same as the voltage applied to
EA+ (pin 5).
[0114] If the instantaneous output of operational amplifier CS
exceeds the output of operational amplifier EA AOUT (pin 11) and
BOUT (pin 14) transistors Q2a and Q2b are turned off. If the
current generated by transistors Q2a and Q2b exceeds the limit set
by feedback circuit 16, controller 18 will temporarily terminate
the gate drives to Q2 and Q2b. This comparison/control function
occurs on a cycle-by-cycle basis.
[0115] CLADJ (pin 1) is used to further limit the current output of
the switching circuit 12. The voltage applied to CLADJ (pin 1)
limits the maximum current output of the switched power converter.
As the voltage applied to CLADJ (pin 1) decreases so does the
maximum current output of the switched power converter. CLADJ (pin
1) is connected to the output of the foldback circuit 42, where the
foldback circuit will cause the current limit to decrease (i.e.
reduce the voltage applied to CLADJ) in a near short circuit
situation. CLADJ (pin 1) is also connected between resistors R14
and R15 which act as a voltage divider circuit. Resistor R14 is
connected to 5 volt reference 5REF and is in series with resistor
R15. Resistor R15 is also connected to ground.
[0116] VREF (pin 2) provides a 5.1 volt reference voltage which
supplies power to various electrical components within the switched
power converter. The output of VREF is identified as 5 volt
reference 5REF. VIN (pin 15) is connected to a power supply for the
purpose of providing power to controller 18. VIN (pin 15) is
connected to Zener diode D9 and capacitor C10 which provide
approximately 15 volts to controller 18. Zener diode D9 and
capacitor C10 receive voltage from unregulated DC terminal 40
through resistors R24a and R24b.
[0117] VC (pin 13) is the power supply for the sales of transistors
Q2a and Q2b through AOUT (pin 11) and BOUT (pin 14), respectively.
VC (pin 13) is connected to VIN (pin 15) through resistor R16.
Resistor R16 is used to limit the current entering VC (pin 13).
Schottky diodes D16a, D15a, D15b and D16b are used to prevent the
voltage on AOUT (pin 11) and BOUT (pin 14) from exceeding VIN or
from dropping below GND.
[0118] GND (pin 12) is connected to ground. Capacitor C25 is
connected to CT (pin 8) and resistor R13 is connected to RT (pin 9)
for setting the frequency and maximum duty cycle of controller 18.
Capacitor C25 and resistor R13 are also connected to ground. SYNC
(pin 10) is not utilized.
Foldback Circuit
[0119] As briefly mentioned, foldback circuit 42 provides feedback
to controller 18 for the purpose of reducing the duty cycle of
transistors Q2a and Q2b under near short circuit conditions rather
than allowing the output current across the DC toad to increase out
of control. Foldback circuit 42 includes, diode D4, resistors R19a,
R19b, R17, and R18, capacitor C8, and operational amplifier U3C.
Operational amplifier U3C has the following connections: pin 8 is
the output, pin 9 is the negative input, pin 10 is the positive
input, pin 4 is connected to 5 volt reference 5REF, and pin 11 is
connected to ground.
[0120] The foldback circuit 42 measures the duty cycle of
transistors Q2a and Q2b. Pin 10 is connected to AOUT (pin 11) and
BOUT (pin 14) on controller 18 through resistors R19aand R19b.
[0121] Capacitor C8, which is connected between pin 10 and ground,
as well as in series with resistors R19a and R19b is used for the
purpose of averaging the duty cycle controlled gate voltages of
transistors Q2a and Q2b. Resistor R17 is connected between 5 volt
reference 5REF and pin 10, and resistor R18 is connected between
pin 10 and ground for the purpose of creating a voltage divider
circuit to reduce the voltage applied to pin 10. Pin 9 is connected
to pin 8 for the purpose of creating a voltage follower, such that
the voltage at pin 8 will always equal the voltage applied to pin
10. Pin 8 is also connected to the cathode of diode D4, and the
anode of diode D4 is connected to CLADJ (pin 1) of controller
18.
[0122] As the duty cycle of AOUT (pin 11) and BOUT (pin 14)
increases, the voltage of capacitor C8 increases as well as the
voltage on pin 10. Accordingly, the voltage on pin 8 will be higher
than the voltage between resistors R15 and R14. When this occurs,
diode D4 will be reverse biased and the voltage at CLADJ (pin 1) of
controller 18 will not be affected. In this situation the current
limit of CLADJ will neither decrease nor increase because foldback
circuit 42 is not pulling current from CLADJ (pin 1).
[0123] As the duty cycle of AOUT (pin 11) and BOUT (pin 14)
decreases, the voltage of capacitor C8 decreases as well as the
voltage on pin 10. Accordingly, the voltage on pin 8 will be lower
than the voltage between resistors R15 and R14. When this occurs,
diode D4 will be forward biased and the voltage at CLADJ (pin 1) of
controller 18 will be pulled down. As the voltage applied to CLADJ
(pin 1) decreases, the maximum current output of controller 18 will
also decrease. Accordingly, in the event of a near short circuit at
the DC load, the reduced current limitation of CLADJ will prohibit
the current output from going unreasonably high and reduce the
output current to less than its previous maximum rating.
Voltage Feedback Circuit
[0124] The feedback circuit 16 measures the voltage across the DC
load and outputs a reference voltage to controller 18. Controller
18 contains an internal voltage controller, for the purpose of
providing a voltage controlled current source. Controller 18 will
control the switching of transistors Q2a and Q2b accordingly.
Feedback circuit 16 includes resistors R28, R34, R32, R26, R25, R33
and R30, capacitors C27, C22, C20, and C28, and optical coupler U2
which includes a LED, a photo-sensor and a 2.5 volt reference.
[0125] When the DC load is increased, there is an immediate drop in
voltage across the DC output terminals of the power converter. This
drop in voltage requires an increase of output current in the
output circuit 44 in order to meet the new load demands.
Alternatively, when the DC load is decreased, there is an immediate
increase in voltage. This increase in voltage requires a decrease
in the output current of the output circuit 44 in order to
compensate for the load reduction.
[0126] For example, when the operator of the switched power
converter brings an additional load on-line, the feedback circuit
16 first measures the voltage across the load and then scales the
voltage down to a 2.5 volt range. Because a new load has been added
the measured voltage will be below the 2.5 voltage range. Optical
coupler U2 will compare the measured voltage (scaled down) against
a 2.5 volt reference. Because the measured voltage across the load
will be below the 2.5 reference voltage, optical coupler U2 will
cause the LED to produce less light. When the LED produces less
light the photo-sensor will cause the output of the feedback
circuit to increase in voltage. The output of the photo-sensor is
connected to EA+ (pin 5) on controller 18. When the voltage input
of EA+ (pin 5) increases, the voltage controller within controller
18 will temporarily increase the duty cycle of the switching
circuit 12. This in turn increases the load current to meet the new
load demand (i.e. get the voltage across the DC load back up to
13.6 volts).
[0127] Alternatively, when the operator of the switched power
converter removes a load, the feedback circuit 16 measures the
voltage across the load and then scales the voltage down to a 2.5
volt range. Because a load has been removed the measured voltage
will be above the 2.5 voltage range. Opto-coupler U2 will compare
the measured voltage (scaled down) against a 2.5 volt reference.
Now, because the measured voltage across the load will be above the
2.5 reference voltage, opto-coupler U2 will cause the LED to
produce additional light. When the LED produces additional light
the output of the feedback circuit will decrease in voltage. The
output of the photo-sensor is connected to EA+ (pin 5) on
controller 18. When the voltage input of EA+ (pin 5) decreases, the
voltage controller within controller 18 will temporarily decrease
the duty cycle of the switching circuit 12. This in turn, decreases
the load current to meet the reduced load demand (i.e. get the
voltage across, the DC load back down to 13.6 volts).
[0128] Resistor R25 limits current to opto-coupler U2. Resistor R26
and R28 are arranged as a voltage divider to provide a scaled
output voltage in the vicinity of 2.5 volts. Capacitors C20, C22,
C27, C28, R34, R32 and R33 are used for stability, do not affect
the DC levels whatsoever as they carry no DC current. Resistor R30
is used for providing an input voltage to EA+ (pin 5) of controller
18 based on the current output of opto-coupler U2.
Current Sensing Circuit
[0129] Current sensing circuit 34 is used to measure the current
being drawn by transistors Q2a and Q2b and to send the measured
current to CS+ (pin 4) of controller 18. Controller 18 then
compares this measured current to a reference level. The reference
level is the output of feedback circuit 16, which is connected to
EA+ (pin 5) on controller 18. Depending upon the measured current
and the reference level, controller 18 will control the on/doff
state of transistors Q2a and Q2b.
[0130] Current sensing circuit 34 includes transformer T4, diodes
D24a, D24b, D24c, and D24d, resistors R21, R21a, R21b, R21c, R21d,
and R21e, and capacitor C9. The drain of transistor Q2b is
connected to pin 4 of transformer T4, and the drain of transistor
Q2a is connected pin 6 of transformer T4. The output side of
transformer T4 (pins 1 and 2) is connected to a series of diodes
and resistors and then to CS+ (pin 4) of controller 18.
[0131] Diodes D24a, D24b, D24c, and D24d make up a full wave
rectifier bridge. Diodes D24c and D24b are connected in parallel to
the output side of transformer T4, where the cathode of diode D24c
is connected to pin 1 of transformer T4 and the cathode of diode
D24b is connected to pin 2 of transformer T4. The anodes of diodes
D24b and D24c are both connected to ground. Diodes D24d and D24a
are also connected in parallel to the output side of transformer
T4, where the anode of diode D24d is connected to pin 1 of
transformer T4 and the anode of diode D24a is connected to pin 2 of
transformer T4. The cathodes of diodes D24a and D24d are connected
to CS+ (pin 4) of controller 18 as well as a series of resistors
and a capacitor.
[0132] For example, when transistor Q2a is turned on, the current
from transformer T4 will flow from pin 1 of the transformer,
through diode D24d and through resistors R21, returning through
D24b to pin 2. A voltage representing the flow of this current
trough R21 is connected to pin 4 of CS+ in controller 18. When
transistor Q2b is turned on, the current from transformer T4 will
flow from pin 2 of the transformer through D24a and through R21 (to
ground) and then returning through R24c to ground to pin 1 of T4.
Again, the voltage on R21 resistors is fed to CS+, the op-amp in
controller 18.
[0133] Resistors R21, R21a, R21b, R21c, R21d, and R21e, and
capacitor C9 are all connected in parallel. The current output of
diodes D24d and D24a are connected to the high side of resistors
R21, R21a, R21b, R21c, R21d, and R21e, and capacitor C9. The low
side of resistors R21, R21a, R21b, R21c, R21d, and R21e, and
capacitor C9 are connected to ground. This parallel
resistor-capacitor circuit is used for the purpose of ensuring the
voltage applied to CS+ (pin 4) of controller 18 is in the 1 volt
range.
Output Circuit
[0134] The secondary-output side of transformer T1 is connected to
the DC load through a series of circuit elements making up the
output rectifier and LC filter circuit 44. The output circuit 44
includes capacitors C19, C11, C13A, C12, C14A, C17, and C18,
schottky diodes D11a and D11b, diode D12, resistor R29, inductor
L2, fuses F2, F3, and F4, inductor beads L3, L4, L10, and L11, and
heavy gauge wires 105, 106, and 107. The DC load is connected in
parallel with capacitors C11, C13A, C12, C14A, C17, and C18 (DC
load capacitors), which are in series with inductor L2. The output
circuit 44 is integral with the transformer secondary and includes
two current loops with the current going in the same direction
through inductor L2, the DC load capacitors, and the DC load (FIG.
17).
[0135] As further illustrated by FIG. 17 when transistor Q2a is
turned on (Q2b is off) current I.sub.1 will flow between pin 4 and
pin 6 (primary-input side of transformer T1) in a counter-clockwise
direction. Current I.sub.1 will cause current I.sub.3 to flow
between pin 8 and pin 1 (secondary side of transformer T1) in a
clockwise direction. Alternatively, when transistor Q2b is turned
on (Q2a is off) current I.sub.2 will flow between pin 4 and pin 5
(primary-input side of transformer T1) in a clockwise direction.
Current I.sub.2 will cause current I.sub.4 to flow between pin 8
and pin 2 (secondary side of transformer T1) in a counter-clockwise
direction. As illustrated the current (I.sub.4 and I.sub.3) applied
to inductor L2 is always going in the same direction.
[0136] Further explained, when transistor Q2a is turned on, current
flows in the secondary-output side of transformer T1 from pin 1
through schottky diode D11a, through inductor L2. The DC load
capacitors will be charged and current will be delivered to the DC
load and back through pin 8 of the transformer. When transistor Q2b
is turned on, current flows in the secondary side of transformer T1
from pin 2 through schottky diode D11b, through inductor L2, the DC
load capacitors will be charged and current will be delivered to
the DC load and then back through pin 8 of the transformer.
[0137] Resistor 29 and capacitor C19 are connected in series
between secondary-output pins 2 and 1 of transformer T1 for the
purpose of eliminating transient voltages. Inductor beads L3, L4,
L10, L11, are connected between the secondary-output side of
transformer T1 and schottky diodes D11a and D11b. Inductor beads
L3, L4, L10 and L11 are placed on the leads of D11A and D11B, for
the purpose of reducing transient noise. The DC load capacitors
which are connected in parallel with the DC load are arranged as
follows. Capacitor C11 is the main output capacitor. The positive
plate of capacitor C11 is connected to the positive terminal of the
DC load P4 and the negative plate is connected to the negative
terminal of the DC load P1.
[0138] The remaining capacitors are used for the purpose of
reducing noise. Capacitor C12 is connected in parallel with the DC
load, where one plate of capacitor C12 is connected to the positive
terminal of the. DC load P4, and the other plate of capacitor C12
is connected to the negative terminal of the DC load P1. Capacitors
C13A and C14A are connected in series, where one plate of capacitor
C13A is connected to the positive terminal of the DC load P4, and
one plate of capacitor C14A is connected to the negative terminal
of the DC load P1. The remaining plates of capacitors C13A and C14A
are connected to chassis ground. Capacitors C17 and C18 are also
connected in series, where one plate of capacitor C17 is connected
to the positive terminal of the DC load P4, and one plate of
capacitor C18 is connected to the negative terminal of the DC load
P1. The remaining plates of capacitors C17 and C18 are connected to
chassis ground. Fuses F2, F3, and F4 are connected in series with
inductor L2 and work in conjunction with diodes D11a and D11b to
provide reverse battery protection.
[0139] The illustrated embodiment of this invention also includes
the use of heavy gauge wires which supplement the copper
laminations on the circuit board. Heavy gauge wires 105 are
connected directly between the negative output (terminal 8) of
transformer T1 and the negative terminal of DC load P1 (i.e. DC
negative output 88) Heavy gauge wires 106 are connected directly
between schottky diodes D11A and the input of inductor L2. Heavy
gauge wires 106 are also connected directly between schottky diodes
D11B and the input of inductor L2. Heavy gauge wires 107 are
connected directly between the output of inductor L2 and fuses F2,
F3, and F4. The output of fuses F2, F3, and F4 are connected to the
positive terminal of DC load P4 (i.e. DC positive output 90).
Waveforms
[0140] FIG. 5 illustrates waveforms found at various points in the
circuit of FIG. 17 under normal operating conditions. FIG. 5A shows
the voltages across the two power transistors Q2a and Q2b during a
complete cycle of operation. One voltage is the complement of the
other. FIG. 5B shows the voltages across the primary windings of
transformer T1 during one complete cycle of switch operation. FIG.
5C illustrates the current waveforms I.sub.1 and I.sub.2 through
the primary loops of FIG. 17.
[0141] FIG. 5D shows the current through inductor L2.
[0142] FIG. 5E shows the secondary current through diode D11a.
[0143] FIG. 5F shows the secondary current 14 through diode
D11b.
[0144] FIG. 5G shows the current through C11.
[0145] FIG. 5H shows the voltage at the top of the circuit of FIG.
17; i.e., the top of L2.
[0146] Permanent Reverse Battery Indicator
[0147] The permanent reverse battery connection indicator 24 is
diode D12. Diode D12 and capacitor C11 are connected in parallel.
The cathode of diode D12 is connected to the positive plate of
capacitor C11 which is connected to the positive terminal of the DC
load P4. The anode of diode D12 is connected to the negative plate
of capacitor C11 which is connected in to the negative terminal of
the DC load P1. If a reverse battery connection is applied to the
DC load output of the power converter, diode D12 will blow before
fuses F2-F4 open circuit, permanently indicating that a reverse
battery connection has occurred. If F2-F4 blow, they may be
replaced or reset and the converter 46 will be fully operational
even if D12 is not replaced.
Packaging a Commercial Device
[0148] Having described the preferred power conversion circuit, the
packaging of a commercial embodiment will be described in detail
with reference to FIGS. 18-26.
[0149] The commercial embodiment of converter 46 comprises a
rectangular sheet metal housing 70 attached by screws to a finned
aluminum extrusion 52 which forms the aforementioned heat sink for
the FET's Q2a and Q2b ,diode D11a and D11b,and the thermistor RT1.
These components are held against a large flat surface 53 of heat
sink 52 by spring clips 55 which are screwed into the heat sink
extrusion in the manner shown in FIG. 19. The fan 32 is mounted by
screws 57 onto an end of the heat sink extrusion 52 in which a
relief 59 of circular design has been machined. The surfaces of the
relief 59 lie below the end surfaces 61 of the fins 65 and the
screw base 63 on which the fan 32 is mounted. This relief creates
an air gap between the fan motor 50 and the heat sink which
prevents heat from the sink reaching the fan motor. Numerous vents
58 are formed in the top and back plates of the housing 70.
[0150] Flanges 84 are provided on both ends of housing 70 for
mounting purposes. Fuses F2-F4 are mounted outside the housing 70
for ease of replacement. Fuse Fx1, however, is inside the housing
for reasons described above. The positive output terminals 90 and
the negative output terminals 88 are mounted on the left side of
housing 70 as shown in FIG. 22. A power cord 98 extends from
housing 70 through aperture 100.
[0151] The components in the circuit of FIG. 2 are mounted on a
conventional circuit board 102 which is secured by fasteners within
housing 70. The board 102 has conductive traces on both sides as
shown in FIGS. 25 and 26. The inductor L2 is mounted on board 102
as shown in FIG. 25 along with the transformer T1.(central in FIG.
25). Two No. 12 gauge wires 104 run from the center tap of T1 to a
point 106 where they pass through a hole in board 102 and emerge on
the other side as shown in FIG. 26. From there to the negative
output terminal 88 the wires overlie a copper trace and are
soldered to the trace to lower the resistance of this high current
path and increase the robustness of it as well. The leads 108 from
L2 to the fuses F2-F4 and the positive outputs 90 are similarly
constructed.
[0152] FIG. 23 shows the converter 46 mounted within an RV 109
having a storage battery 114. A power cord 112 brings 115 vac to
the converter from a pedestal 111 of the type found in RV parks.
The converter 46 is connected into the electrical system of the RV
in a known manner.
[0153] Referring again to FIG. 2 the circuit for the converter 46
is here equipped with a 4-wire terminal H2 of which pin 4 is
connected to the converter output fuses. F2-F4 via a 100 Ohm
resistor R57. The terminal H2 allows the converter to be connected
to an external "management" system of the type described in U.S.
Pat. No. 5,982,643 issued Nov. 9, 1999 to Thomas H. Phlipot and
assigned to Progressive Dynamics, Inc. As is more completely
described in the '643 patent, the management system includes a
microcontroller which gives the owner the option of various
operating modes and various converter output voltages; e.g., 13.6 v
for normal operation, 13.2 v for storage, and 14.4 v for boost.
Miscellaneous--Options
[0154] FIG. 2 also illustrates a terminal H4 connected to ground
via R51, R31 and C21. Terminal H4 is a two-contact terminal which
is shorted out with a small bridge wire if a gel cell is used in
place of the normal lead-acid liquid storage battery 114 in the RV.
This lowers the operating voltages of the converter 46 by 0.4 v and
is a convenient option for owners who wish to use gel cell storage
batteries
[0155] While the present invention has been described in connection
with what is presently considered to be the most practical and
preferred embodiment, it is to be understood that the invention is
not to be limited to the disclosed embodiments but, on the contrary
is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended
claims, which scope is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures
as is permitted under the law. It is also to be understood that it
is the inventor's intent to claim all novel subject matter
contained within this disclosure.
TABLE-US-00001 VALUES OF LISTED COMPONENTS C1 Capacitor 0.47 uF C10
Capacitor 220 uF C11 Capacitor 16 V C12 Capacitor 0.01 uF C13A
Capacitor 0.01 uF C14A Capacitor 0.01 uF C15 Capacitor 2.2 nF C16
Capacitor 2.2 nF C17 capacitor 0.047 uF C18 capacitor 0.047 uF C19
capacitor 0.001 uF C2 capacitor 2.2 nF C20 capacitor 0.015 uF C22
capacitor 0.47 uF C24 capacitor 270 pF C25 capacitor 0.12 uF, 2%
C26 capacitor 0.47 uF C27 capacitor 1000 pF C28 capacitor 0.1 uF
C29 capacitor 2.2 nF C3 capacitor 2.2 nF C30 capacitor 0.47 uF C31
capacitor 2.2 nF C4a capacitor 820 uF, 250 V C4b capacitor 820 uF,
250 V C4c capacitor 820 uF, 250 V C5 capacitor 100 uF, 35 V C7
capacitor 0.1 uF C8 capacitor 0.1 uF C9 capacitor 0.01 uF D10 zener
diode 13 V D11a schottky diode 40 A, 100 V D11b schottky diode 40
A, 100 V D12 diode D15a schottky diode 1 A, 20 V D15b schottky
diode 1 A, 20 V D16a schottky diode 1 A, 20 V D16b schottky diode 1
A, 20 V D1a schottky diode 1 A, 100 V D23 zener diode 220 V, 5 W,
5% D24a diode 75 V, 150 mA D24b diode 75 V, 150 mA D24c diode 75 V,
150 mA D24d diode 75 V, 150 mA D27 schottky diode 1 A, 20 V D3
schottky diode 1 A, 20 V D4 diode 75 V, 150 mA D9 zener diode 15 V,
2 W DB1 diode bridge 20 A, 400 V Bridge F1 fuse 15 A F2 fuse 30 A
F3 fuse 30 A F4 fuse 30 A Fx1 fuse 0.5 A L2 inductor 20 uH Q1
transistor 5 A, 40 V Q2a transistor 24 A, 500 V, .20 on resistance
Q2b transistor 24 A, 500 V, .20 on resistance R1 resistor 390 Ohm,
5% R13 resistor 1.82 K R14 resistor 16.2 K R15 resistor 35.7 K R16
resistor 1.8 K, 5% R17 resistor 5.49 K R18 resistor 15.4 K R19a
resistor 12.1 K R19b resistor 12.1 K R20 resistor 50 Ohm, 5%, 3 W
R21 resistor 18.7 Ohm R21A resistor 422 Ohm R21B resistor 422 Ohm
R21C resistor 845 Ohm R21D resistor 845 Ohm R21E resistor 1690 Ohm
R23a resistor 15 Ohm, 5% R23b resistor 15 Ohm, 5% R24a resistor 1.5
K, 5%, 10 W R24b resistor 1.5 K, 5%, 10 W R25 resistor 1 K, 5%, 1/2
W R26 resistor 31.2 K or 30.1 K R28 resistor 6.98 K, 1/4% R29
resistor 10 Ohm, 5% R2a resistor 453 K R30 resistor 4.7 K R33
resistor 3.24 K R34 resistor 3.24 K R37 resistor 100 Ohm, 5%, 10 W
R38 resistor 84.5 K, 0.5 W R39 resistor 866 Ohm R4 resistor 22.6 K
R40 resistor 97.6 K R7 resistor 32.4 K R8 resistor 499 K RN1A
resistor 16.2 K RN1B resistor 47.5 K RN1C resistor 9.53 K RT1
thermistor 100 K RT2 thermistor 1 Ohm T1 transformer 2:13:13:2:2 T2
CMC transformer custom T3 CMC transformer custom T4 transformer 80
MH U2 optically isolated amplifier FOD2741 USA operational
amplifier LM2902 U3B operational amplifier LM2902 U3C operational
amplifier LM2902 U3D operational amplifier LM2902
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