U.S. patent application number 11/526384 was filed with the patent office on 2008-03-27 for phase-control power controller for converting a line voltage to a rms load voltage.
This patent application is currently assigned to OSRAM SYLVANIA INC.. Invention is credited to Matthew B. Ballenger, George B. Kendrick, Ernest C. Weyhrauch.
Application Number | 20080074053 11/526384 |
Document ID | / |
Family ID | 39238970 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080074053 |
Kind Code |
A1 |
Weyhrauch; Ernest C. ; et
al. |
March 27, 2008 |
Phase-control power controller for converting a line voltage to a
RMS load voltage
Abstract
A phase-control power controller converts a line voltage to an
RMS load voltage and includes a phase-control clipping circuit that
clips a load voltage to provide the RMS load voltage. The power
controller may be in a base of a lamp and connected to a lamp
terminal. The phase-clipping circuit establishes a phase conduction
angle that determines the RMS load voltage for the lamp and
includes a transistor switch and a microcontroller that operates
the transistor switch, where ON/OFF periods of the transistor
switch define the phase conduction angle. The microcontroller
senses a load voltage at the lamp terminal, compares the sensed
load voltage to a reference RMS voltage, and adjusts the ON/OFF
periods of the transistor switch in response to the comparison to
cause the load voltage to approach the reference RMS voltage. The
circuit may be used for reverse, forward, or forward/reverse hybrid
phase clipping.
Inventors: |
Weyhrauch; Ernest C.;
(Richmond, KY) ; Ballenger; Matthew B.;
(Lexington, KY) ; Kendrick; George B.; (Lexington,
KY) |
Correspondence
Address: |
OSRAM SYLVANIA INC
100 ENDICOTT STREET
DANVERS
MA
01923
US
|
Assignee: |
OSRAM SYLVANIA INC.
Danvers
MA
|
Family ID: |
39238970 |
Appl. No.: |
11/526384 |
Filed: |
September 25, 2006 |
Current U.S.
Class: |
315/209SC |
Current CPC
Class: |
H05B 39/048 20130101;
Y02B 20/148 20130101; Y02B 20/00 20130101 |
Class at
Publication: |
315/209SC |
International
Class: |
F02P 7/03 20060101
F02P007/03 |
Claims
1. A phase-control power controller that converts a line voltage to
a RMS load voltage, the controller comprising: line terminals for a
line voltage and load terminals for a load voltage; and a
phase-clipping circuit connected to said line and load terminals
and establishing a phase conduction angle that determines an RMS
load voltage, said phase-clipping circuit comprising a transistor
switch and a microcontroller that operates said transistor switch,
wherein ON/OFF periods of said transistor switch define the phase
conduction angle, said microcontroller being arranged and adapted
to sense the load voltage and to compare the sensed load voltage to
a reference RMS voltage and to adjust the ON/OFF periods of said
transistor switch in response to the comparison to cause the load
voltage to approach the reference RMS voltage.
2. The controller of claim 1, wherein said microcontroller causes
said transistor switch to be ON immediately before and after a
polarity change of the load voltage and OFF when the load voltage
is at a peak between adjacent polarity changes.
3. The controller of claim 1, wherein said microcontroller causes
said transistor switch to be ON immediately following a polarity
change of the load voltage and OFF when the load voltage is at a
peak and until the next polarity change.
4. The controller of claim 1, wherein said microcontroller causes
said transistor switch to be OFF immediately following a polarity
change of the load voltage and through a peak load voltage and then
ON until the next polarity change.
5. The controller of claim 1, wherein said phase-control circuit
comprises a full-wave bridge.
6. The controller of claim 1, wherein said microcontroller
comprises an analog-to-digital converter that converts a waveform
of the sensed load voltage to a digital signal.
7. The controller of claim 1, wherein said microcontroller is
arranged and adapted to provide a positive polarity signal to a
gate of said transistor switch when said transistor switch is
ON.
8. The controller of claim 1 in an integrated circuit that is
connected between a terminal of a lamp and a light emitting element
of said lamp.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is directed to a power controller that
supplies a specified power to a load, and more particularly to a
voltage converter for a lamp that converts line voltage to a
voltage suitable for lamp operation.
[0002] Some loads, such as lamps, operate at a voltage lower than a
line (or mains) voltage of, for example, 120V or 220V, and for such
loads a voltage converter (or power controller) that converts line
voltage to a lower operating voltage must be provided. The power
supplied to the load may be controlled with a phase-control
clipping circuit that typically includes an RC circuit. Moreover,
some loads operate most efficiently when the power is constant, or
substantially so. However, line voltage variations are magnified by
these phase-control clipping circuits due to their inherent
properties (as will be explained below) and the phase-control
clipping circuit is desirably modified to provide a more nearly
constant RMS load voltage.
[0003] A simple four-component RC phase-control clipping circuit
demonstrates a problem of conventional phase-control clipping
circuits. The phase-controlled clipping circuit shown in FIG. 1 has
a capacitor 22, a diac 24, a triac 26 that is triggered by the diac
24, and resistor 28. The resistor 28 may be a potentiometer that
sets a resistance in the circuit to control a phase at which the
triac 26 fires.
[0004] In operation, a clipping circuit such as shown in FIG. 1 has
two states. In the first state the diac 24 and triac 26 operate in
the cutoff region where virtually no current flows. Since the diac
and triac function as open circuits in this state, the result is an
RC series network such as illustrated in FIG. 2. Due to the nature
of such an RC series network, the voltage across the capacitor 22
leads the line voltage by a phase angle that is determined by the
resistance and capacitance in the RC series network. The magnitude
of the capacitor voltage V.sub.C is also dependent on these
values.
[0005] The voltage across the diac 24 is analogous to the voltage
drop across the capacitor 22 and thus the diac will fire once
breakover voltage V.sub.BO is achieved across the capacitor. The
triac 26 fires when the diac 24 fires. Once the diac has triggered
the triac, the triac will continue to operate in saturation until
the diac voltage approaches zero. That is, the triac will continue
to conduct until the line voltage nears zero crossing. The virtual
short circuit provided by the triac becomes the second state of the
clipping circuit as illustrated in FIG. 3.
[0006] Triggering of the triac 26 in the clipping circuit is
forward phase-controlled by the RC series network and the leading
portion of the line voltage waveform is clipped until triggering
occurs as illustrated in FIGS. 4-5. A load attached to the clipping
circuit experiences this clipping in both voltage and current due
to the relatively large resistance in the clipping circuit.
[0007] Accordingly, the RMS load voltage and current are determined
by the resistance and capacitance values in the clipping circuit
since the phase at which the clipping occurs is determined by the
RC series network and since the RMS voltage and current depend on
how much energy is removed by the clipping.
[0008] With reference to FIG. 6, clipping is characterized by a
conduction angle .alpha. and a delay angle .theta.. The conduction
angle is the phase between the point on the load voltage/current
waveforms where the triac begins conducting and the point on the
load voltage/current waveform where the triac stops conducting.
Conversely, the delay angle is the phase delay between the leading
line voltage zero crossing and the point where the triac begins
conducting.
[0009] Define V.sub.irrms as RMS line voltage, V.sub.orms as RMS
load voltage, T as period, and .omega. as angular frequency (rad)
with .omega.=27.pi.f.
[0010] Line voltage may vary from location to location up to about
10% and this variation can cause a harmful variation in RMS load
voltage in the load (e.g., a lamp). For example, if line voltage
were above the standard for which the voltage conversion circuit
was designed, the triac 26 may trigger early thereby increasing RMS
load voltage. In a halogen incandescent lamp, it is particularly
desirable to have an RMS load voltage that is nearly constant.
[0011] Changes in the line voltage are exaggerated at the load due
to a variable conduction angle, and conduction angle is dependent
on the rate at which the capacitor voltage reaches the breakover
voltage of the diac. For fixed values of frequency, resistance and
capacitance, the capacitor voltage phase angle (.theta..sub.C) is a
constant defined by .theta..sub.C=arctan (-.omega.RC). Therefore,
the phase of V.sub.C is independent of the line voltage magnitude.
However, the rate at which V.sub.C reaches V.sub.BO is a function
of V.sub.irrms and is not independent of the line voltage
magnitude.
[0012] FIG. 7 depicts two possible sets of line voltage V.sub.i and
capacitor voltage V.sub.C. As may be seen therein, the rate at
which V.sub.C reaches V.sub.BO varies depending on V.sub.irrms. For
RC phase-control clipping circuits the point at which
V.sub.C=V.sub.BO is of concern because this is the point at which
diac/triac triggering occurs. As V.sub.irrms increases, V.sub.C
reaches V.sub.BO earlier in the cycle leading to an increase in
conduction angle (.alpha..sub.2>.alpha..sub.1), and as
V.sub.irrms decreases, V.sub.C reaches V.sub.BO later in the cycle
leading to a decrease in conduction angle
(.alpha..sub.2<.alpha..sub.1).
[0013] Changes in V.sub.irrms leading to exaggerated or
disproportional changes in V.sub.orrms are a direct result of the
relationship between conduction angle and line voltage magnitude.
As V.sub.irrms increases, V.sub.orrms increases due to both the
increase in peak voltage and the increase in conduction angle, and
as V.sub.irrms decreases, V.sub.orrms decreases due to both the
decrease in peak voltage and the decrease in conduction angle.
Thus, load voltage is influenced twice, once by a change in peak
voltage and once by a change in conduction angle, resulting in
unstable RMS load voltage conversion for the simple phase-control
clipping circuit.
[0014] When the phase-control power controller is used in a voltage
converter of a lamp, the voltage converter may be provided in a
fixture to which the lamp is connected or within the lamp itself.
U.S. Pat. No. 3,869,631 is an example of the latter, in which a
diode is provided in the lamp base for clipping the line voltage to
reduce RMS load voltage at the light emitting element. U.S. Pat.
No. 6,445,133 is another example of the latter, in which
transformer circuits are provided in the lamp base for reducing the
load voltage at the light emitting element.
SUMMARY OF THE INVENTION
[0015] An object of the present invention is to provide a novel
phase-control power controller that converts a line voltage to an
RMS load voltage and uses a microcontroller to adjust the voltage
conversion in response to variations in line voltage magnitude.
[0016] A further object is to provide a novel phase-control power
controller with a phase-control clipping circuit that establishes a
phase conduction angle that determines an RMS load voltage, where
the phase-clipping circuit includes a transistor switch and a
microcontroller that operates the transistor switch, where ON/OFF
periods of the transistor switch define the phase conduction angle,
and in which the microcontroller senses the load voltage and
compares the sensed load voltage to a reference RMS voltage and
adjusts the ON/OFF periods of the transistor switch in response to
the comparison to cause the load voltage to approach the reference
RMS voltage. The circuit may be used for reverse, forward, or
forward/reverse hybrid phase clipping.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic circuit diagram of a phase-controlled
clipping circuit of the prior art.
[0018] FIG. 2 is a schematic circuit diagram of the
phase-controlled dimming circuit of FIG. 1 showing an effective
state in which the triac is not yet triggered.
[0019] FIG. 3 is a schematic circuit diagram of the
phase-controlled dimming circuit of FIG. 1 showing an effective
state in which the triac has been triggered.
[0020] FIG. 4 is a graph illustrating current clipping in the
phase-controlled dimming circuit of FIG. 1.
[0021] FIG. 5 is a graph illustrating voltage clipping in the
phase-controlled dimming circuit of FIG. 1.
[0022] FIG. 6 is a graph depicting the conduction angle convention
for forward phase clipping.
[0023] FIG. 7 is a graph showing how changes in the magnitude of
the line voltage affect the rate at which capacitor voltage reaches
the diac breakover voltage.
[0024] FIG. 8 is a partial cross section of an embodiment of a lamp
of the present invention.
[0025] FIG. 9 is a schematic circuit diagram showing an embodiment
of the power controller of the present invention.
[0026] FIG. 10 is a circuit diagram of a more particular embodiment
of the present invention.
[0027] FIG. 11 is a graph depicting forward/reverse hybrid clipping
of the present invention, including the clipped load voltage and
the control voltage from the microcontroller.
[0028] FIG. 12 is a graph depicting the conduction angle convention
for forward/reverse hybrid clipping.
[0029] FIG. 13 is a graph depicting reverse clipping of the present
invention, including the clipped load voltage and the control
voltage from the microcontroller.
[0030] FIG. 14 is a graph depicting the conduction angle convention
for reverse clipping.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0031] With reference to FIG. 8, a lamp 10 includes a base 12 with
a lamp terminal 14 that is adapted to be connected to line (mains)
voltage, a light-transmitting envelope 16 attached to the base 12
and housing a light emitting element 18 (an incandescent filament
in the embodiment of FIG. 8), and a voltage conversion circuit 20
for converting a line voltage at the lamp terminal 14 to a lower
operating voltage. The voltage conversion circuit 20 may be
entirely within the base 12 and connected between the lamp terminal
14 and the light emitting element 18 (that is, the voltage
conversion circuit 20 may be entirely within the part of the lamp
that is arranged and adapted to fit into a lamp socket, such as
shown in FIG. 8). The voltage conversion circuit 20 may be an
integrated circuit in a suitable package as shown schematically in
FIG. 8.
[0032] While FIG. 8 shows the voltage conversion circuit 20 in a
parabolic aluminized reflector (PAR) halogen lamp, the voltage
conversion circuit 20 may be used in any incandescent lamp when
placed in series between the light emitting element (e.g.,
filament) and a connection (e.g., lamp terminal) to a line voltage.
Further, the voltage conversion circuit described and claimed
herein finds application other than in lamps and is not limited to
lamps. It may also be used more generally where resistive or
inductive loads (e.g., motor control) are present to convert an
unregulated AC line or mains voltage at a particular frequency or
in a particular frequency range to a regulated RMS load voltage of
specified value.
[0033] With reference to FIG. 9 that illustrates an embodiment of
the present invention, the voltage conversion circuit 20 includes
line terminals 32 for a line voltage and load terminals 34 for a
load voltage, a phase-clipping circuit 36 that is connected to the
line and load terminals and establishes a phase conduction angle
that determines the RMS load voltage. The circuit 36 includes a
transistor switch 38, a full-wave bridge 40, and a microcontroller
42 that sends signals to a gate of the transistor switch 38 that
cause the transistor switch to be ON during times periods that
define the phase conduction angle for the circuit 36. The
microcontroller 42 is arranged and adapted to sense the load
voltage and to compare the sensed load voltage to a reference RMS
voltage and to adjust the ON/OFF periods of the transistor switch
38 in response to the comparison to cause the load voltage to
approach the reference RMS voltage.
[0034] Conventional RC phase-control clipping circuits are very
sensitive to fluctuations in the line voltage magnitude. The
present invention provides a power controller that makes
adjustments in response to changes in the line voltage magnitude by
changing the ON periods of the transistor switch that triggers
conduction in response to sensed changes, thereby reducing
variation of the RMS load voltage compared to conventional RC
phase-control circuits. Additionally, this control technique makes
it possible to use a forward/reverse hybrid of phase-control
clipping by which the effects of electromagnetic interference (EMI)
and total harmonic distortion (THD) are reduced in comparison to
forward-only phase-control clipping.
[0035] Microcontroller 42 preferably includes an analog-to-digital
converter (ADC) that converts the load voltage to a digital signal,
a comparator that compares the output from the ADC to the reference
RMS voltage (or a corresponding reference value), and a program
(e.g., in a hardwired and/or programmable circuit) that adjusts the
ON time of the transistor switch to adjust the RMS load voltage
based on an output from the comparator so as to approach the
reference RMS voltage. The ADC is connected to the load voltage
through a current limiting resistor. The microcontroller samples
the load voltage waveform applied to the lamp and automatically
increases or decreases the conduction times such that the RMS load
voltage is nearly always at a desired level. The reference RMS
voltage is preset to a value that provides the desired RMS load
voltage for the lamp. The structure and operation of
microcontroller 42 need not be described in detail as such
microcontrollers are known in the art and are commercially
available from various sources, including Microchip Technology,
Inc. under the PIC trademark (e.g., a PIC.TM. 8-pin 8-bit CMOS
microcontroller, such as PIC 12F683).
[0036] With reference now to FIG. 10, a particular embodiment of
the present invention includes a full-wave bridge 44, an insulated
gate bipolar transistor 46 (which alternatively may be a MOSFET),
and a programmable microcontroller 48 (e.g., a PIC.TM.
microcontroller) that includes an analog-to-digital converter. The
microcontroller 48 monitors the voltage on the output line and
automatically adjusts the duty cycle of the transistor switch such
that the RMS load voltage supplied to the lamp filament is
constantly at the desired level. Inputs to the microcontroller 48
may be provided by including appropriate circuitry such as the
connections, resistors and capacitors in FIG. 10, which are shown
by way of example. A heat sink (not shown) may be attached to the
transistor switch as needed.
[0037] The phase-clipping circuit may be used for reverse, forward,
or forward/reverse hybrid phase clipping. With reference to FIG.
11, the microcontroller may control the transistor switch to
provide forward/reverse hybrid phase clipping that removes power
from the region of the load voltage cycle near the peak of the
cycle between polarity changes, without clipping the leading and
trailing edges. The signals should have a positive polarity at the
gate of the transistor switch to provide the hybrid clipping.
[0038] With reference to FIG. 12, the forward/reverse hybrid phase
clipping is defined as clipping that removes power from the region
of the load voltage cycle near the peak of the cycle between
polarity changes, without clipping the leading and trailing edges.
That is, clipping occurs in the region shown in FIG. 12 between the
conduction angle .alpha..sub.1 and the conduction angle
.alpha..sub.2. As is apparent, together the two conduction angles
.alpha..sub.1 and .alpha..sub.2 form a conduction region that spans
a polarity change of the load voltage. The signals from the
microcontroller to the transistor switch are timed to provide this
hybrid clipping.
[0039] Alternatively and with reference to FIG. 13, the
microcontroller may control the transistor switch to provide
reverse phase clipping that removes power from the region of the
load cycle from near the peak until the next polarity change. The
conduction angle convention for reverse clipping is shown in FIG.
14 wherein the conduction angle .alpha. is shown in the region of
the load cycle immediately following a polarity change.
[0040] Similarly, the microcontroller may be used to control the
transistor switch to provide forward phase clipping that removes
power from the region of the load cycle from a polarity change and
through a peak load voltage. The conduction angle convention for
reverse clipping is shown in FIG. 6 wherein the conduction angle
.alpha. is shown in the region of the load cycle immediately before
a polarity change.
[0041] While embodiments of the present invention have been
described in the foregoing specification and drawings, it is to be
understood that the present invention is defined by the following
claims when read in light of the specification and drawings.
* * * * *