U.S. patent application number 14/846313 was filed with the patent office on 2017-03-09 for input and output overvoltage protection in a power converter.
The applicant listed for this patent is Power Integrations, Inc.. Invention is credited to Yury Gaknoki, Zongqi Hu, Arthur B. Odell, Tiziano Pastore, Sundaresan Sundararaj.
Application Number | 20170070142 14/846313 |
Document ID | / |
Family ID | 58056827 |
Filed Date | 2017-03-09 |
United States Patent
Application |
20170070142 |
Kind Code |
A1 |
Sundararaj; Sundaresan ; et
al. |
March 9, 2017 |
INPUT AND OUTPUT OVERVOLTAGE PROTECTION IN A POWER CONVERTER
Abstract
A controller for use in a power converter includes a gate drive
circuit coupled to generate a control signal to switch a power
switch of the power converter. A zero current detection circuit is
coupled to a multifunction pin coupled to receive a multifunction
signal that is representative of an input voltage of the power
converter when the power switch is on, and representative of an
output voltage of the power converter when the power switch is off.
The zero current detection circuit is coupled to generate a zero
current detection signal. An overvoltage detection circuit is
coupled to receive the multifunction signal and a state signal
representative of a state of the power switch to generate in
response to the state signal and the multifunction signal a line
overvoltage signal and an output over voltage signal coupled to be
received by the gate drive circuit.
Inventors: |
Sundararaj; Sundaresan;
(Union City, CA) ; Hu; Zongqi; (Fremont, CA)
; Pastore; Tiziano; (Los Gatos, CA) ; Gaknoki;
Yury; (San Jose, CA) ; Odell; Arthur B.;
(Morgan Hill, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Power Integrations, Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
58056827 |
Appl. No.: |
14/846313 |
Filed: |
September 4, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 1/32 20130101; H02M
3/156 20130101 |
International
Class: |
H02M 3/157 20060101
H02M003/157 |
Claims
1. A controller for use in a power converter, comprising: a gate
drive circuit coupled to generate a control signal to switch a
power switch of the power converter to control a transfer of energy
of from an input of the power converter through an energy transfer
element to an output of the power converter; a zero current
detection circuit coupled to a multifunction pin coupled to receive
a multifunction signal from the power converter, wherein the
multifunction signal is representative of an input voltage of the
power converter when the power switch is on, and wherein the
multifunction signal is representative of an output voltage of the
power converter when the power switch is off, wherein the zero
current detection circuit is coupled to generate in response to the
multifunction signal a zero current detection signal coupled to be
received by the gate drive circuit; and an overvoltage detection
circuit coupled to the multifunction pin to receive the
multifunction signal from the power converter, wherein the
overvoltage detection circuit is further coupled to the gate drive
circuit to receive a state signal representative of a state of the
power switch, wherein the overvoltage detection circuit is coupled
to generate in response to the state signal and the multifunction
signal a line overvoltage signal and an output overvoltage signal
coupled to be received by the gate drive circuit, wherein the gate
drive circuit is coupled to disable switching of the power switch
in response to the output overvoltage signal or the line
overvoltage signal.
2. The controller of claim 1, further comprising a virtual short
circuit coupled to the multifunction pin, wherein the virtual short
circuit is coupled to provide a virtual short circuit current to
the multifunction pin in response to the multifunction signal
decreasing to a negative value.
3. The controller of claim 2, wherein the virtual short circuit
comprises: a ground sense amplifier having a first input coupled to
the multifunction pin to receive the multifunction signal, and a
second input coupled to a ground reference; and a current source
coupled to provide the virtual short circuit current to the
multifunction pin in response to an output of the ground sense
amplifier.
4. The controller of claim 1, wherein the zero current detection
circuit comprises: a reference comparator having a first input
coupled to the multifunction pin to receive the multifunction
signal, and a second input coupled to a voltage reference; a first
comparator coupled to be activated or deactivated in response to an
output of the reference comparator to compare the multifunction
signal with a voltage threshold reference; a second comparator
coupled to be deactivated or activated in response to the output of
the reference comparator to compare the multifunction signal with a
rate of change threshold signal; and a logic gate having a first
input coupled to an output of the first comparator, and a second
input coupled to an output of the second comparator, wherein the
logic gate is coupled to generate the zero current detection signal
in response to the first comparator and the second comparator.
5. The controller of claim 4, wherein the zero current detection
circuit further comprises a high pass filter, wherein the second
comparator is coupled to receive the multifunction signal through
the high pass filter when the second comparator is activated.
6. The controller of claim 1, wherein the overvoltage detection
circuit comprises: a third comparator coupled to be activated or
deactivated in response to the state signal to compare the
multifunction signal with a line overvoltage current reference to
generate the line overvoltage signal; a fourth comparator coupled
to be deactivated or activated in response to the state signal to
compare the multifunction signal with a overvoltage reference to
generate the output overvoltage signal.
7. The controller of claim 1, wherein the power switch is included
in the controller.
8. The controller of claim 1, wherein the power converter is a buck
converter.
9. The controller of claim 8, wherein the power switch is a high
side switch of the buck converter.
10. The controller of claim 8, wherein the power switch is a low
side switch of the buck converter.
11. The controller of claim 1, wherein the multifunction signal is
coupled to be received from through a first resistor having a first
end coupled to the multifunction pin, and a second end coupled to
be responsive to the output of the power converter, wherein a
second resistor is coupled between the multifunction pin and a
local return.
12. A power converter, comprising: an energy transfer element
coupled between an input of the power converter and an output of
the power converter; a power switch coupled to the input of the
power converter and the energy transfer element; and a controller,
wherein the controller includes: a gate drive circuit coupled to
generate a control signal to switch the power switch to control a
transfer of energy of from the input of the power converter through
the energy transfer element to the output of the power converter; a
zero current detection circuit coupled to a multifunction pin
coupled to receive a multifunction signal of the power converter,
wherein the multifunction signal is representative of an input
voltage of the power converter when the power switch is on, and
wherein the multifunction signal is representative of an output
voltage of the power converter when the power switch is off,
wherein the zero current detection circuit is coupled to generate
in response to the multifunction signal a zero current detection
signal coupled to be received by the gate drive circuit; and an
overvoltage detection circuit coupled to the multifunction pin to
receive the multifunction signal from the power converter, wherein
the overvoltage detection circuit is further coupled to the gate
drive circuit to receive a state signal representative of a state
of the power switch, wherein the overvoltage detection circuit is
coupled to generate in response to the state signal and the
multifunction signal a line overvoltage signal and an output over
voltage signal coupled to be received by the gate drive circuit,
wherein the gate drive circuit is coupled to disable switching of
the power switch in response to the output overvoltage signal or
the line overvoltage signal.
13. The power converter of claim 12, wherein the controller further
comprises a virtual short circuit coupled to the multifunction pin,
wherein the virtual short circuit is coupled to provide a virtual
short circuit current to the multifunction pin in response to the
multifunction signal decreasing to a negative value.
14. The power converter of claim 13, wherein the virtual short
circuit comprises: a ground sense amplifier having a first input
coupled to the multifunction pin to receive the multifunction
signal, and a second input coupled to a ground reference; and a
current source coupled to provide the virtual short circuit current
to the multifunction pin in response to an output of the ground
sense amplifier.
15. The power converter of claim 12, wherein the zero current
detection circuit comprises: a reference comparator having a first
input coupled to the multifunction pin to receive the multifunction
signal, and a second input coupled to a voltage reference; a first
comparator coupled to be activated or deactivated in response to an
output of the reference comparator to compare the multifunction
signal with a voltage threshold reference; a second comparator
coupled to be deactivated or activated in response to the output of
the reference comparator to compare the multifunction signal with a
rate of change threshold signal; and a logic gate having a first
input coupled to an output of the first comparator, and a second
input coupled to an output of the second comparator, wherein the
logic gate is coupled to generate the zero current detection signal
in response to the first comparator and the second comparator.
16. The power converter of claim 15, wherein the zero current
detection circuit further comprises a high pass filter, wherein the
second comparator is coupled to receive the multifunction signal
through the high pass filter when the second comparator is
activated.
17. The power converter of claim 12, wherein the overvoltage
detection circuit comprises: a third comparator coupled to be
activated or deactivated in response to the state signal to compare
the multifunction signal with a line overvoltage current reference
to generate the line overvoltage signal; a fourth comparator
coupled to be deactivated or activated in response to the state
signal to compare the multifunction signal with a overvoltage
reference to generate the output overvoltage signal.
18. The power converter of claim 12, wherein the power switch is
included in the controller.
19. The power converter of claim 12, wherein the power converter is
a buck converter.
20. The power converter of claim 12, further comprising: a first
resistor having a first end coupled to the multifunction pin, and a
second end coupled to be responsive to the output of the power
converter, wherein the multifunction pin is coupled to receive the
multifunction signal through the first resistor; and a second
resistor is coupled between the multifunction pin and a local
return.
Description
BACKGROUND INFORMATION
[0001] Field of the Disclosure
[0002] The present invention relates generally to power converters,
and more specifically controllers that can detect an input and
output of a power converter from a single pin.
[0003] Background
[0004] Electronic devices use power to operate. Switched mode power
converters are commonly used due to their high efficiency, small
size and low weight to power many of today's electronics.
Conventional wall sockets provide a high voltage alternating
current. In a switch mode power converter, a high voltage
alternating current (ac) input is converted to provide a
well-regulated direct current (dc) output through an energy
transfer element. The switched mode power converter control circuit
usually provides output regulation by sensing one or more inputs
representative of one or more output quantities and controlling the
output in a closed loop. In operation, a switch is utilized to
provide the desired output by varying the duty cycle (typically the
ratio of the on time of the switch to the total switching period),
varying the switching frequency, or varying the number of pulses
per unit time of the switch in a switched mode power converter.
[0005] Power converters are occasionally exposed to surges in the
received input voltage, which is generally referred to as an
overvoltage condition. Input and output overvoltages can be
dangerous in power supplies: input voltages going too high may
cause high voltage (HV) switches to fail due to high voltage and
high current conditions occurring at the same time, with the switch
failing even below its breakdown voltage. Excessive output voltage
may cause electrical overstress on the output capacitors,
electrolytic in most cases, which may cause it to fail causing fire
or other hazards. Furthermore, light emitting diode (LED) bulb
manufacturers sometimes perform production tests with the LED load
disconnected. In this situation, the bulb (with its driver
circuitry) should survive and not degrade lifetime expectations. In
this case, it's crucial to minimize stress on output electrolytic
capacitor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Non-limiting and non-exhaustive embodiments of the present
invention are described with reference to the following figures,
wherein like reference numerals refer to like parts throughout the
various views unless otherwise specified.
[0007] FIG. 1 is a block diagram illustrating one example of a
power converter, in accordance with the teachings of the present
disclosure.
[0008] FIG. 2A is a block diagram of one example of a controller
for a power converter illustrating a detailed example of a virtual
short circuit, in accordance with the teachings of the present
disclosure.
[0009] FIG. 2B is a block diagram of one example of a controller
for a power converter illustrating detailed examples of an
overvoltage detection circuit and a zero current detection circuit,
in accordance with the teachings of the present disclosure.
[0010] FIG. 3 is an example timing diagram illustrating the voltage
at a single terminal that can detect the input voltage and output
voltage when the input voltage is above a threshold, in accordance
with the teachings of the present disclosure.
[0011] FIG. 4 is another example timing diagram illustrating the
voltage at a single terminal that can detect the input voltage and
output voltage when the input voltage is below a threshold, in
accordance with the teachings of the present disclosure.
[0012] FIG. 5 is a block diagram illustrating another example of a
power converter, in accordance with the teachings of the present
disclosure.
[0013] FIG. 6 is a block diagram illustrating yet another example
of a power converter, in accordance with the teachings of the
present disclosure.
[0014] FIG. 7 is a block diagram illustrating still another example
of a power converter, in accordance with the teachings of the
present disclosure.
[0015] Corresponding reference characters indicate corresponding
components throughout the several views of the drawings. Skilled
artisans will appreciate that elements in the figures are
illustrated for simplicity and clarity and have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements in the figures may be exaggerated relative to other
elements to help to improve understanding of various embodiments of
the present invention. Also, common but well-understood elements
that are useful or necessary in a commercially feasible embodiment
are often not depicted in order to facilitate a less obstructed
view of these various embodiments of the present invention.
DETAILED DESCRIPTION
[0016] Examples of power converters in which the inputs and outputs
are protected from overvoltage conditions are described herein. In
the following description, numerous specific details are set forth
in order to provide a thorough understanding of the present
invention. It will be apparent, however, to one having ordinary
skill in the art that the specific detail need not be employed to
practice the present invention. In other instances, well-known
materials or methods have not been described in detail in order to
avoid obscuring the present invention.
[0017] Reference throughout this specification to "one embodiment",
"an embodiment", "one example" or "an example" means that a
particular feature, structure or characteristic described in
connection with the embodiment or example is included in at least
one embodiment of the present invention. Thus, appearances of the
phrases "in one embodiment", "in an embodiment", "one example" or
"an example" in various places throughout this specification are
not necessarily all referring to the same embodiment or example.
Furthermore, the particular features, structures or characteristics
may be combined in any suitable combinations and/or subcombinations
in one or more embodiments or examples. Particular features,
structures or characteristics may be included in an integrated
circuit, an electronic circuit, a combinational logic circuit, or
other suitable components that provide the described functionality.
In addition, it is appreciated that the figures provided herewith
are for explanation purposes to persons ordinarily skilled in the
art and that the drawings are not necessarily drawn to scale.
[0018] Referring to FIG. 1, a functional block diagram of an
example power converter 100 is illustrated in accordance with the
teachings of the present invention. In the depicted example, power
converter 100 is implemented as a buck converter, which includes an
input filter capacitor C.sub.IN 108 coupled to a rectified input
voltage V.sub.IN 102, a high side switch S1 122, a controller 126,
a sense resistor Rs 124, a resistor R1 130, a resistor R2 132, a
rectifier D1 110, an energy transfer element L1 120, which is
coupled between the input and the output of the power converter
100, an output capacitor C.sub.O 112, a load 114, an input return
116, and a local return 127 as shown. It is appreciated that the
high side switch S1 122, which is coupled to the input of the power
converter and to the energy transfer element L1 120, may also be
referred to as a power switch, or a main switch. In one example,
controller 126 further includes a multifunction M pin 129, a zero
current detection circuit 134, an inverter 140, an overvoltage
detection circuit 136, a gate drive circuit 150, virtual short
circuit 170, and nodes 180, 182.
[0019] FIG. 1 further illustrates an example in which energy
transfer element current IL 160 is implemented with an inductor,
and multifunction M pin 129 coupled to receive a multifunction
signal U.sub.MF 128. As shown in the example, multifunction signal
U.sub.MF 128 is coupled to be received through a resistor R2 132.
In the depicted example, one end of resistor R2 132 is coupled to
multifunction M pin 129, and a second end of resistor R2 132
coupled to be responsive to an output of power converter 100 as
shown. In addition, a resistor R1 130 is coupled between
multifunction M pin 129 and the local return 127 as shown.
Controller 126 further includes a switch current signal U.sub.SWC
152, an output overvoltage signal U.sub.OOVL 144, a state signal
U.sub.STATE 146, a line overvoltage signal U.sub.LOVL 148, a zero
current detection signal U.sub.ZCD 142, and a control signal
U.sub.GS 154.
[0020] Power converter 100 may further include a high side positive
rail and low side negative rail coupled to receive rectified
voltage V.sub.IN 102. In one example, input filter capacitor
C.sub.IN 108 may be included to provide a switching noise filtering
function. For power converters with power factor correction (PFC),
a small input filter capacitor C.sub.IN 108 may be coupled between
the high side positive rail and low side negative rail to allow the
filtered voltage to substantially follow the rectified input
voltage. In other words, the capacitance of input filter may be
selected such that when the rectified input voltage V.sub.IN 102
substantially reaches zero, the voltage on the input filter
capacitor C.sub.IN 108 may also substantially reach zero.
[0021] Power converter 100 may further include controller 126
coupled to control switch S1 122 via control signal U.sub.GS 154 to
control a transfer of energy from the input of power converter 100
to the output of power converter 100 through energy transfer
element L1 120. In the example depicted in FIG. 1, the input of
power converter 100 is coupled to receive input voltage V.sub.IN
102, and load 114 is coupled to the output of power converter 100
to receive output voltage V.sub.O 118. Controller 126 may be
located on the high side positive rail and may be coupled to
multifunction signal U.sub.MF 128 through multifunction M pin 129.
In some examples, multifunction signal U.sub.MF 128 may be
representative of output voltage V.sub.O 118, when switch S1 122 is
open. Multifunction signal U.sub.MF 128 may also be representative
of the input voltage V.sub.IN 102, when switch S1 122 is closed.
More discussion on how multifunction signal U.sub.MF 128 can sense
an input voltage or an output voltage will be discussed in FIG. 2A
and FIG. 2B.
[0022] In one example, current sense resistor R.sub.S 124 is
coupled to one end of the switch S1 122, and another end is coupled
to a cathode side of diode D1 110. The current sense resistor RS
124 provides a switch current signal U.sub.SWC 152 to the
controller 126. In the depicted example, the switch current signal
U.sub.SWC 152 provides a signal value representative of the current
in switch S1 122.
[0023] In one example, controller 126 is coupled to generate
control signal U.sub.GS 154 to control switching of switch S1 122
between an on state (e.g., a state in which current is
substantially allowed to flow through switch S1 122) and an off
state (e.g., a state in which current is substantially prevented
from flowing through switch S1 122) in response to control signal
U.sub.GS 154. Controller 126 may disable switching of switch S1 122
when an output overvoltage occurs, a line overvoltage occurs, or
both occur, in accordance with the teachings of the present
invention.
[0024] In operation, when switch S1 122 is turned on, current may
flow into inductor L1 120, thereby charging output capacitor
C.sub.O 112. The voltage across the inductor L1 120 is proportional
to V.sub.IN-V.sub.O, and the current flowing out of the
multifunction M pin 129. In one example, controller 126 creates a
virtual short between the multifunction M pin 129 and the end of
switch S1 122 that is directly coupled to local return 127. To
illustrate, the example depicted in FIG. 1 shows that controller
126 includes a virtual short circuit 170 coupled to multifunction M
pin 129. In the example, that virtual short circuit 170 is coupled
to provide a current when the voltage at the multifunction M pin
129 decreases to a negative value. The offset current provided by
the virtual short circuit 170 takes a path from node 182 to node
180. The offset current I.sub.C 135 is provided by the virtual
short circuit 170 to the M pin 129 increases the voltage at M pin
128 back to zero, thus creating a virtual short between the
multifunction M pin 129 and the end of switch S1 122 that is
directly coupled to local return 127. With the virtual short
between multifunction M pin 129 and local return 127, a current
I.sub.MF can be derived for the U.sub.MF signal 128 as
I MF = V IN - V O R 2 . ( 1 ) ##EQU00001##
[0025] When switch S1 is closed, controller 126 may be able to
detect when a line overvoltage condition occurs if I.sub.MF exceeds
a threshold value. In one example, the threshold value may be 1
milliamp. If a line overvoltage is detected, controller 126 may
disable switching and perform an auto-restart.
[0026] In operation, when switch S1 122 is open, current flows
through the inductor L1 120, output capacitor C.sub.O 112 and load
114. The current then returns through rectifier D1 110, thereby
ramping down while energy in inductor L1 120 discharges. During the
flywheel conduction time, the output voltage measured by V.sub.MF
can be expressed for the U.sub.MF signal 128 as
V MF = V OUT * R 1 R 1 + R 2 . ( 2 ) ##EQU00002##
[0027] An output overvoltage condition may have occurred if
multifunction signal U.sub.MF--128 exceeds a threshold value. If an
output overvoltage is detected for several consecutive cycles,
controller 126 may disable switching and perform an auto-restart.
For instance, in one example, if an overvoltage is detected for
four consecutive switching cycles, then controller 126 may disable
switching and perform the auto-restart. In one example, the output
voltage threshold value may be 2.4 volts. In one example, the value
of R2 may be 400 k.OMEGA.. In one example the value of R1 is
fifteen times less than R2, which in this example is equivalent to
26.67 k.OMEGA..
[0028] The multifunction signal U.sub.MF 128 may provide a signal
to controller 126 for when the switch S1 122 needs to be turned on
or off. In one example, controller 126 includes a zero current
detection circuit 134 coupled to receive the multi-function signal
U.sub.MF 128. In one example, the zero current detection circuit
134 of controller 126 is coupled to detect when inductor L1 160 is
about to be demagnetized. A negative edge triggered zero current
detection signal U.sub.ZCD 142 is provided to the gate drive
circuit 150 for switching of S1 122 to occur.
[0029] FIG. 2A illustrates an example of a controller 236, which is
similar to controller 126 as shown in FIG. 1, and further
illustrating the virtual short circuit 270 included therein. As
shown in the depicted example, controller 236 includes of a zero
current detection circuit 234, an overvoltage detection circuit
236, an inverter 240, a gate drive circuit 250, virtual short
circuit 270, and nodes 280, 282. Controller 236 also includes a
multifunction M pin 229, which is coupled to receive a
multifunction signal U.sub.MF 228.
[0030] As shown in the depicted example, virtual short circuit 270
includes a ground sense amplifier 222, a current source 224 coupled
to a supply voltage V.sub.BP 225, and a transistor 226. In one
example, the supply voltage V.sub.BP 225 may be connected to a
bypass pin of controller 236. Ground sense amplifier 222 is coupled
to receive the U.sub.MF signal 228 at the inverting input terminal
and a ground reference 231 is coupled to the non-inverting input
terminal. As such, when the U.sub.MF signal 228 drops to a negative
value, ground sense amplifier 222 turns on transistor 226.
Transistor 226 delivers an offset current I.sub.C 235 from current
source 224. The offset current takes the path from node 282 to node
280. The offset current I.sub.C 235 brings the voltage at
multifunction M pin 229 back to zero.
[0031] FIG. 2B illustrates an example of controller 236, which is
also similar for example to controller 126 as shown in FIG. 1, and
illustrates increased detailed examples of a zero current detection
circuit 234, and an overvoltage detection circuit 236. As shown in
the depicted example, controller 236 includes a zero current
detection circuit 234, an overvoltage detection circuit 236, an
inverter 240, a gate drive circuit 250, virtual short circuit 270,
and nodes 280, 282. Gate drive circuit 250 is coupled to receive a
zero current signal U.sub.ZCD 242, a switch current signal
U.sub.SWC 252, a line overvoltage signal U.sub.LOVL 248, and an
output overvoltage signal U.sub.OOVL 244. Gate drive circuit 250 is
coupled to output the control signal U.sub.GS 254 and the state
signal U.sub.STATE 246. As shown in the depicted example, the
U.sub.STATE 246 signal is representative of a state of the switch
S1 122. In the example, U.sub.STATE 246 signal may close a switch
coupled to current comparator 258 and activate current comparator
258, and open a switch coupled to voltage comparator 260 and
deactivate voltage comparator 260 when U.sub.STATE 246 is a logic
high. In addition, the U.sub.STATE 246 signal may open the switch
coupled to current comparator 258 and deactivate current comparator
258, and close the switch coupled to voltage comparator 260 and
activate voltage comparator 260 when U.sub.STATE signal 246 is a
logic low. For example, a logic high U.sub.STATE 246 signal may
represent the switch S1 122 being closed, and a logic low signal
U.sub.STATE 246 signal may represent the switch S1 122 being
open.
[0032] In the example illustrated in FIG. 2B, multifunction signal
U.sub.MF 228 is also coupled to provide a signal to current
comparator 258, and voltage comparator 260 as shown. In one
example, controller 236 may convert multifunction signal U.sub.MF
228 into a current signal or voltage signal. When high side switch
S1 122 is on, there exists a virtual short between the
multifunction signal and one end of switch S1 122 as discussed
above.
[0033] Current comparator 258 determines if a line overvoltage has
occurred by measuring the current I.sub.MF as expressed above in
equation 1. Multifunction signal U.sub.MF 228 is coupled to the
inverting terminal of current comparator 258, and a current
reference I.sub.LOV 272 is coupled to the non-inverting terminal of
current comparator 258. In one example, the current reference value
of I.sub.LOV 272 may be representative of 1 milliamp. If
multifunction signal U.sub.MF 228 is above the current reference
value I.sub.LOV 272, current comparator 258 outputs a logic high
signal U.sub.LOVL 248 to the gate drive circuit 250. If
multifunction signal U.sub.MF 228 is below the current reference
value I.sub.LOV 272, comparator 258 outputs a logic low signal for
U.sub.LOVL 248 to the gate drive circuit 250. In one example, the
logic high signal U.sub.LOVL 248 to the gate drive circuit 250
indicates that a line overvoltage has occurred, and gate drive
circuit 250 disables switching of the switch S1 122 in response
thereto.
[0034] Voltage comparator 260 determines if an output overvoltage
has occurred by measuring a voltage signal of U.sub.MF 228.
Multifunction signal U.sub.MF 228 is coupled to the inverting
terminal of voltage comparator 260, and a voltage reference
V.sub.OREF 274 is coupled to the non-inverting terminal of voltage
comparator 260. In one example, the value of V.sub.OREF 274 may be
representative of 2.4 volts. If multifunction signal U.sub.MF 228
is above the voltage reference V.sub.OREF 274 value, voltage
comparator 260 outputs a logic high signal U.sub.OOVL 244. If
signal V.sub.MF 228 is below the voltage reference V.sub.OREF 274
value, voltage comparator 260 outputs a logic low signal for
U.sub.OOVL 244 to the gate drive circuit 250. In one example, the
logic high signal U.sub.OOVL 244 to the gate drive circuit 250
indicates that an output overvoltage has occurred, and gate drive
circuit 250 disables switching of the of switch S1 122 in response
thereto.
[0035] The example depicted in FIG. 2B also shows that one example
of zero current detection circuit 234 includes a first comparator
256, a second comparator 258, a reference comparator 267, a high
pass filter 264, and a logic gate 262. In one example, to ensure
the buck converter is operating in a critical conduction mode, the
gate drive circuit 250 is coupled to immediately turn on switch S1
122 when the inductor L1 120 has been demagnetized. Zero current
detection circuit 234 may determine the inductor L1 120 has been
demagnetized if the multifunction signal U.sub.MF 228 falls below a
threshold or exceeds a rate of change.
[0036] Zero current detection circuit 234 may determine the input
voltage during the on time of switch S1 122. Reference comparator
267 may output a signal to close a switch coupled to the first
comparator 256 to activate the first comparator 256, and open a
switch coupled to the second comparator 258 to deactivate the
second comparator 258. Reference comparator 267 may output a signal
to open a switch coupled to the first comparator 256 to deactivate
the first comparator 256, and close a switch coupled to the second
comparator 258 to activate the second comparator 258. As shown in
the depicted example, current reference I.sub.REF 266 is coupled to
the non-inverting input terminal of reference comparator 267, and
multifunction signal U.sub.MF 228 is coupled to the inverting input
terminal of reference comparator 267. In one example, multifunction
signal U.sub.MF 228 is converted to a voltage signal for this
operation.
[0037] If the multifunction signal U.sub.MF 228 is above the
current reference I.sub.REF 266, this may indicate the input
voltage is greater than double of the output voltage. In this case,
reference comparator 267 closes a switch coupled to first
comparator 256, and opens a switch coupled to second comparator
258.
[0038] First comparator 256 is coupled to the voltage threshold
reference V.sub.TH 269 at the inverting input, and the
multifunction signal U.sub.MF 228 at the non-inverting input. First
comparator 256 may determine if multifunction signal U.sub.MF 228
falls below the voltage threshold reference V.sub.TH 269. In one
example, the value of voltage threshold reference V.sub.TH 269 may
be representative of 0.25 volts. First comparator 256 may output a
logic low signal when multifunction signal U.sub.MF 228 is above
the voltage threshold reference V.sub.TH 269 to logic gate 262.
First comparator 256 may output a logic high signal when signal
U.sub.MF 228 is below the voltage threshold reference V.sub.TH to
logic 262. The output signal U.sub.ZCD 242 of the logic gate is
coupled to the gate drive circuit 250 to enable controller 236 to
switch S1 122.
[0039] If the multifunction signal U.sub.MF 228 is below the
current reference I.sub.REF 266, this may indicate the input
voltage is not greater than double of the output voltage. In this
case, reference comparator 267 opens the switch coupled to first
comparator 256, and closes the switch coupled to second comparator
258.
[0040] Zero current detection circuit 234 may determine if the
multifunction U.sub.MF signal 228 exceeds a rate of change. For
instance, in the depicted example, second comparator circuit 258 is
coupled to receive the multifunction U.sub.MF signal 228 at the
non-inverting input through a high pass filter 264 coupled to the
switch of comparator 258 as shown. Second comparator circuit 258 is
also coupled to receive a rate of change threshold signal V.sub.DTH
268 at the inverting input as shown to detect a rate change of the
multifunction U.sub.MF signal 228. In one example, the second
comparator 258 utilizes rate of change threshold signal V.sub.DTH
268 to detect a rate change of 1 V/1 .mu.s of the multifunction
U.sub.MF 228 signal. If the U.sub.MF signal 228 exceeds rate of
change threshold signal V.sub.DTH 268, second comparator 258 may
output a logic high signal to logic gate 262. If the multifunction
U.sub.MF signal 228 does not exceed rate of change threshold signal
V.sub.DTH 268, rate change circuit may output a logic low signal to
logic gate 262. The output of logic gate 262 outputs the signal
U.sub.ZCD 242 that is coupled to the gate drive circuit 250 to
indicate to controller 236 to switch S1 122 via gate signal
U.sub.GS 254.
[0041] Logic gate 262 is coupled to receive a signal from the first
comparator 256 and a signal from second comparator 258. In one
example, logic gate 262 is an OR gate. Logic gate 262 outputs a
signal to inverter 240, and that inverted signal U.sub.ZCD 242 is
received by the gate drive circuit 250 to turn on the switch S1 for
the next conduction cycle.
[0042] FIG. 3 is an example timing diagram illustrating the voltage
at a single terminal that can detect the input voltage and output
voltage when the input voltage is above a threshold, in accordance
with the teachings of the present disclosure. In particular, FIG. 3
illustrates the controller switch S1 based on the multifunction
signal U.sub.MF 302. In this case, the input voltage is greater
than double of the output voltage the operation, and therefore
comparator 256 is activated. Multifunction signal U.sub.MF 302 may
be represented by the waveform. As multifunction signal U.sub.MF
302 falls below a threshold value T.sub.H1 305, the next switching
cycle will begin shortly. The inductor current I.sub.L 360 is
represented in FIG. 3. The next switching cycle occurs when
inductor current I.sub.L reaches zero current. State signal
U.sub.STATE 346 represents the current state of the switch. A logic
high signal of U.sub.STATE 346 represents the switch as closed, and
a logic low represents the switch as open. As U.sub.STATE 346
switches to a high state, energy in the inductor is stored and
inductor current I.sub.L 360 charges linearly. When U.sub.STATE 346
switches to a low state, inductor current I.sub.L discharges.
[0043] FIG. 4 is an example timing diagram illustrating the voltage
at a single terminal that can detect the input voltage and output
voltage when the input voltage is below a threshold, in accordance
with the teachings of the present disclosure. In particular, FIG. 4
illustrates the controller switching based on the multifunction
signal U.sub.MF 428 when the input voltage is less than double of
the output voltage. As multifunction signal U.sub.MF 428 falls
greater than a rate change, the next switching cycle will begin
shortly. The inductor current of L1 460 may discharge at a rate
faster than the rate shown in FIG. 3. State signal U.sub.STATE 446
represents the current state of the switch. A logic high signal of
U.sub.STATE 446 represents the switch as closed, and a logic low
represents the switch as open. As U.sub.STATE 446 switches to a
high state, inductor current I.sub.L 460 charges.
[0044] FIG. 5 is a block diagram illustrating another example of a
power converter 500, in accordance with the teachings of the
present disclosure. It is appreciated that the example power
converter 500 illustrated in FIG. 5 is similar to power converter
100 illustrated in FIG. 1, except that switch S1 122 has been
replaced by a switch Q1 522. In one example, the switch Q1 522 is
an n-channel MOSFET. In this example, the switch Q1 is included in
a monolithic package including the controller of 526. In one
example, switch of Q1 522 may also be a discrete switch. The
operation of power converter 500 as described in FIGS. 1-4 remains
the same.
[0045] FIG. 6 is a block diagram illustrating yet another example
of a power converter 600, in accordance with the teachings of the
present disclosure. It is appreciated that the example power
converter 600 illustrated in FIG. 6 is similar to power converter
500 illustrated in FIG. 5, except that controller 636 has been
moved to the low side. As shown in the depicted example, power
converter 600 further includes an auxiliary winding of energy
transfer element including a primary winding 623 and a secondary
winding 625. The secondary winding 625 is further coupled to a
local return 616, which provides the multifunction signal U.sub.MF
628 to controller 636. Primary winding is used to block a
continuous DC error voltage that appears across the multifunction
pin 629. The operation of power converter 600 as described in FIGS.
1-4 remains the same.
[0046] FIG. 7 is a block diagram illustrating still another example
of a power converter 700, in accordance with the teachings of the
present disclosure. It is appreciated that the example power
converter 700 illustrated in FIG. 7 is similar to power converter
600 illustrated in FIG. 6, except that instead of an auxiliary
winding of energy transfer element including a primary winding 623
and a secondary winding 625, a blocking capacitor 725 is
substituted. The waveform sensed by the divider network is
equivalent to an ac voltage across inductor L1 720. The operation
of power converter 700 as described in FIGS. 1-4 remains the
same.
[0047] The above description of illustrated examples of the present
invention, including what is described in the Abstract, are not
intended to be exhaustive or to be limitation to the precise forms
disclosed. While specific embodiments of, and examples for, the
invention are described herein for illustrative purposes, various
equivalent modifications are possible without departing from the
broader spirit and scope of the present invention. Indeed, it is
appreciated that the specific example voltages, currents,
frequencies, power range values, times, etc., are provided for
explanation purposes and that other values may also be employed in
other embodiments and examples in accordance with the teachings of
the present invention.
[0048] These modifications can be made to examples of the invention
in light of the above detailed description. The terms used in the
following claims should not be construed to limit the invention to
the specific embodiments disclosed in the specification and the
claims. Rather, the scope is to be determined entirely by the
following claims, which are to be construed in accordance with
established doctrines of claim interpretation. The present
specification and figures are accordingly to be regarded as
illustrative rather than restrictive.
* * * * *