# US 2014/0192569 A1 · Overvoltage protection circuit

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- Number: US 2014/0192569 A1
- Document ID: US20140192569A1
- Status: Published application
- Kind: A1
- Application number: 13/736,596
- Filed: 2013-01-08
- Published: 2014-07-10
- Earliest claimed: 2013-01-08
- Assignees: Power Integrations, Inc.
- Inventors: Marvin Cruz ESPINO
- Web page: https://patentgrep.com/patent/US20140192569A1

## CPC

- H02M 3/33515: {with digital control}
- G01R 19/1659: {to indicate that the value is within or outside a predetermined range of values (window) (G01R19/16514, G01R19/16519, G01R19/16528 and G01R19/16533 take precedence)}
- H02H 7/1213: {for DC-DC converters}
- H02M 1/08: Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M 1/32: Means for protecting converters other than automatic disconnection
- H02M 3/33507: {with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence)}
- H02M 1/0009: {Devices or circuits for detecting current in a converter}
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H)

## Abstract

Apparatus and methods for generating an overvoltage signal from a bias winding signal of a power converter transformer are disclosed. In one example, an overvoltage protection circuit may include a current augmentation circuit and a detection circuit. The current augmentation circuit may be coupled to receive the bias winding signal, which may be representative of the power converter output. The current augmentation circuit may include a threshold circuit and a filter circuit that may generate a filtered level shifted signal from the bias winding signal. The current augmentation circuit may generate an augmented signal from the filtered level shifted signal. The detection circuit may be coupled to receive the augmented signal and to generate an overvoltage signal by comparing the augmented signal with a reference voltage. When high asserted, the overvoltage signal may indicate a potential overvoltage condition at the output of the power converter.

## Claims

### Claim 1

An overvoltage detection circuit for a power converter, the circuit comprising:
a threshold circuit coupled to receive a sense signal representative of an output voltage of the power converter only during a portion of an off time of a power switch of the power converter, wherein the threshold circuit is operable to reduce a voltage of the sense signal to output a level shifted sense signal;
a filter circuit coupled to receive the level shifted sense signal from the threshold circuit, wherein the filter circuit is operable to filter the level shifted sense signal to output a filtered level shifted sense signal; and
a detection circuit coupled to an input terminal for receiving the filtered level shifted sense signal from the filter circuit and a power signal representative of a rectified version of the sense signal, wherein the detection circuit is operable to output an overvoltage detection signal based at least in part on the filtered level shifted sense signal, the overvoltage detection signal being representative of an overvoltage condition in the output voltage of the power converter.

### Claim 2 (depends on 1)

The overvoltage detection circuit of claim 1, wherein the threshold circuit comprises:
a first diode, wherein an anode of the first diode is coupled to receive the sense signal; and
a first Zener diode, wherein a cathode of the first Zener diode is coupled to a cathode of the first diode, wherein the threshold circuit is operable to output the level shifted sense signal at an anode of the first Zener diode.

### Claim 3 (depends on 1)

The overvoltage detection circuit of claim 1, wherein the filter circuit comprises:
a first resistor, wherein a first terminal of the first resistor is coupled to receive the level shifted sense signal; and
a first capacitor coupled between a second terminal of the first resistor and ground, wherein the filter circuit is operable to output the filtered level shifted sense signal at the second terminal of the first resistor.

### Claim 4 (depends on 1)

The overvoltage detection circuit of claim 1, wherein the detection circuit comprises:
a clamp circuit coupled to receive the filtered level shifted sense signal from the filter circuit, wherein the clamp circuit is operable to output a comparison signal; and
a comparator coupled to receive the comparison signal from the clamp circuit, wherein the comparator is operable to output the overvoltage detection signal based on a comparison of the comparison signal with a reference voltage.

### Claim 5 (depends on 4)

The overvoltage detection circuit of claim 4, wherein the clamp circuit comprises:
a second Zener diode, wherein the cathode of the second Zener diode is coupled to receive the filtered level shifted sense signal; and
a second resistor coupled between an anode of the second Zener diode and ground, wherein the clamp circuit is operable to output the comparison signal at the anode of the second Zener diode.

### Claim 6 (depends on 4)

The overvoltage detection circuit of claim 4, wherein the comparator comprises an operational amplifier, and wherein a non-inverting terminal of the operational amplifier is coupled to receive the comparison signal from the clamp circuit and an inverting terminal of the operational amplifier is coupled to receive the reference voltage.

### Claim 7 (depends on 1)

The overvoltage detection circuit of claim 1, further comprising:
a power circuit coupled to receive the sense signal representative of the output voltage of the power converter, wherein the power circuit is operable to output the power signal, and wherein the input terminal is further coupled to receive the power signal from the power circuit.

### Claim 8 (depends on 7)

The overvoltage detection circuit of claim 7, wherein the power circuit comprises:
a second diode, wherein an anode of the second diode is coupled to receive the sense signal;
a second capacitor coupled between a cathode of the second diode and ground; and
a third resistor, wherein a first terminal of the third resistor is coupled to the cathode of the second diode, and wherein the power circuit is operable to output the power signal at a second terminal of the third resistor.

### Claim 9 (depends on 1)

The overvoltage detection circuit of claim 1, wherein the detection circuit is included within the controller of the power converter, and wherein the threshold circuit and the filter circuit are external to the controller of the power converter.

### Claim 10 (depends on 1)

The overvoltage detection circuit of claim 1, wherein the filter circuit is included within the detection circuit.

### Claim 11

A power converter, comprising:
a power switch;
a controller for controlling the power switch to regulate the power converter; and
an overvoltage detection circuit comprising:
a threshold circuit coupled to receive a sense signal representative of an output voltage of the power converter only during a portion of an off time of the power switch, wherein the threshold circuit is operable to reduce a voltage of the sense signal to output a level shifted sense signal;
a filter circuit coupled to receive the level shifted sense signal from the threshold circuit, wherein the filter circuit is operable to filter the level shifted sense signal to output a filtered level shifted sense signal; and
a detection circuit coupled to an input terminal of the controller for receiving the filtered level shifted sense signal from the filter circuit and a power signal representative of a rectified version of the sense signal, wherein the detection circuit is operable to output an overvoltage detection signal based at least in part on the filtered level shifted sense signal, the overvoltage detection signal being representative of an overvoltage condition in the output voltage of the power converter.

### Claim 12 (depends on 11)

The power converter of claim 11, wherein the threshold circuit comprises:
a first diode, wherein an anode of the first diode is coupled to receive the sense signal; and
a first Zener diode, wherein a cathode of the first Zener diode is coupled to a cathode of the first diode, wherein the threshold circuit is operable to output the level shifted sense signal at an anode of the first Zener diode.

### Claim 13 (depends on 11)

The power converter of claim 11, wherein the filter circuit comprises:
a first resistor, wherein a first terminal of the first resistor is coupled to receive the level shifted sense signal; and
a first capacitor coupled between a second terminal of the first resistor and ground, wherein the filter circuit is operable to output the filtered level shifted sense signal at the second terminal of the first resistor.

### Claim 14 (depends on 11)

The power converter of claim 11, wherein the detection circuit comprises:
a clamp circuit coupled to receive the filtered level shifted sense signal from the filter circuit, wherein the clamp circuit is operable to output a comparison signal; and
a comparator coupled to receive the comparison signal from the clamp circuit, wherein the comparator is operable to output the overvoltage detection signal based on a comparison of the comparison signal with a reference voltage.

### Claim 15 (depends on 14)

The power converter of claim 14, wherein the clamp circuit comprises:
a second Zener diode, wherein the cathode of the second Zener diode is coupled to receive the filtered level shifted sense signal; and
a second resistor coupled between an anode of the second Zener diode and ground, wherein the clamp circuit is operable to output the comparison signal at the anode of the second Zener diode.

### Claim 16 (depends on 14)

The power converter of claim 14, wherein the comparator comprises an operational amplifier, and wherein a non-inverting terminal of the operational amplifier is coupled to receive the comparison signal from the clamp circuit and an inverting terminal of the operational amplifier is coupled to receive the reference voltage.

### Claim 17 (depends on 11)

The power converter of claim 11, further comprising:
a power circuit coupled to receive the sense signal representative of the output voltage of the power converter, wherein the power circuit is operable to output the power signal, and wherein the input terminal is coupled to receive the power signal from the power circuit.

### Claim 18 (depends on 17)

The power converter of claim 17, wherein the power circuit comprises:
a second diode, wherein an anode of the second diode is coupled to receive the sense signal;
a second capacitor coupled between a cathode of the second diode and ground; and
a third resistor, wherein a first terminal of the third resistor is coupled to the cathode of the second diode, and wherein the power circuit is operable to output the power signal at a second terminal of the third resistor.

### Claim 19 (depends on 11)

The power converter of claim 11, wherein the detection circuit is included within the controller, and wherein the threshold circuit and filter circuit are external to the controller.

### Claim 20 (depends on 11)

The power converter of claim 11, wherein the filter circuit is included within the detection circuit.

### Claim 21

A method for detecting an overvoltage condition at an output of a power converter, the method comprising:
receiving a sense signal from a bias winding of a transformer representative of an output voltage of a power converter only during a portion of an off time of a power switch of the power converter;
reducing a voltage of the sense signal by a threshold circuit to generate a level shifted sense signal;
filtering the level shifted sense signal by a filter circuit to generate a filtered level shifted sense signal;
generating an augmented sense signal based on the filtered level shifted sense signal;
receiving, at an input terminal, the augmented sense signal and a power signal representative of a rectified version of the sense signal, wherein the power signal is used to at least partially power a controller of the power converter; and
generating an overvoltage signal based at least in part on to the augmented sense signal, the overvoltage detection signal being representative of an overvoltage condition in the output voltage of the power converter.

### Claim 22 (depends on 21)

The method of claim 21, wherein the threshold circuit comprises:
a first diode, wherein an anode of the first diode is coupled to receive the sense signal; and
a first Zener diode, wherein a cathode of the first Zener diode is coupled to a cathode of the first diode, wherein the threshold circuit is operable to output the level shifted sense signal at an anode of the first Zener diode.

### Claim 23 (depends on 21)

The method of claim 21, wherein the filter circuit comprises:
a first resistor, wherein a first terminal of the first resistor is coupled to receive the level shifted sense signal; and
a first capacitor coupled between a second terminal of the first resistor and ground, wherein the filter circuit is operable to output the filtered level shifted sense signal at the second terminal of the first resistor.

### Claim 24 (depends on 21)

The method of claim 21, wherein generating an overvoltage signal based at least in part on the augmented sense signal comprises:
generating, by a clamp circuit, a comparison signal from the augmented sense signal; and
comparing, by a comparator, the comparison signal with a reference voltage, wherein the comparator is operable to output the overvoltage signal based on the comparison.

### Claim 25 (depends on 24)

The method of claim 24, wherein the clamp circuit comprises:
a second Zener diode, wherein the cathode of the second Zener diode is coupled to receive the augmented sense signal; and
a second resistor coupled between an anode of the second Zener diode and ground, wherein the clamp circuit is operable to output the comparison signal at the anode of the second Zener diode.

### Claim 26 (depends on 24)

The method of claim 24, wherein the comparator comprises an operational amplifier, and wherein a non-inverting terminal of the operational amplifier is coupled to receive the comparison signal from the clamp circuit and an inverting terminal of the operational amplifier is coupled to receive the reference voltage.

### Claim 27 (depends on 21)

The method of claim 21, further comprising:
generating, by a power circuit, the power signal from the sense signal; and
generating the overvoltage signal based on both the augmented sense signal and the power signal.

### Claim 28 (depends on 27)

The method of claim 27, wherein the power circuit comprises:
a second diode, wherein an anode of the second diode is coupled to receive the sense signal;
a second capacitor coupled between a cathode of the second diode and ground; and
a third resistor, wherein a first terminal of the third resistor is coupled to the cathode of the second diode, and wherein the power circuit is operable to output the power signal at a second terminal of the third resistor.

### Claim 29 (depends on 21)

The method of claim 21, wherein the threshold circuit and the filter circuit are external to the controller of the power converter, and wherein generating an overvoltage signal based on the augmented sense signal is done within the controller of the power converter.