# US 11,451,152 B2 · Active clamp circuit with steering network

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- Number: US 11,451,152 B2
- Document ID: US11451152B2
- Status: Granted
- Kind: B2
- Application number: 17/181,347
- Filed: 2021-02-22
- Published: 2021-06-10
- Granted: 2022-09-20
- Earliest claimed: 2019-11-15
- Assignees: Power Integrations, Inc.
- Applicants: Power Integrations, Inc.
- Inventors: Arthur B. Odell
- Web page: https://patentgrep.com/patent/US11451152B2

## CPC

- H02M 3/33507: {with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence)}
- H02M 1/34: Snubber circuits
- H02M 3/33592: {having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer}
- H02M 1/0054: {Transistor switching losses (periodically suspending operation of switching converter in low power mode H02M1/0035)}
- H02M 1/0058: {by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero (using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826)}
- H02M 1/342: {Active non-dissipative snubbers}
- 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)

## Abstract

A power converter, comprising an energy transfer element, an output of the power converter, a power switch, an active clamp circuit, and a first controller. The active clamp circuit comprising a capacitance, a steering diode network coupled to the capacitance and configured to transfer a charge to the capacitance, a clamp switch coupled to the capacitance and configured to transfer the charge stored in the capacitance to the energy transfer element, and an offset element coupled to the clamp switch and configured to provide a path to discharge a capacitance associated with the clamp switch. The first controller configured to output a clamp drive signal to control the turn on and turn off of the clamp switch and a primary drive signal to control the turn on and turn off of the power switch.

## Claims

### Claim 1

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 energy transfer element;
an active clamp circuit coupled to the energy transfer element and the power switch, the active clamp circuit comprising:
a capacitance,
a steering diode network coupled to the capacitance to transfer a charge to the capacitance;
a clamp switch coupled to the capacitance to transfer the charge stored in the capacitance to the energy transfer element;
an offset element coupled to the clamp switch to provide a path to discharge a capacitance associated with the clamp switch; and
a first controller coupled to the active clamp circuit and to the power switch, and configured to output a clamp drive signal to control the turn on and turn off of the clamp switch and to output a primary drive signal to control the turn on and turn off of the power switch, wherein the first controller is configured to turn on and turn off the clamp switch prior to the turn on of the power switch.

### Claim 2 (depends on 1)

The power converter of claim 1, the steering diode network comprising:
a first diode coupled between the capacitance and the power switch, an anode of the first diode coupled to the power switch, and a cathode of the first diode coupled to the capacitance; and
a second diode coupled between the clamp switch and the power switch, an anode of the second diode coupled to the clamp switch, and a cathode of the second diode coupled to the power switch, wherein the first diode is coupled to transfer charge to the capacitance and the second diode is coupled to transfer charge from the capacitance to the energy transfer element.

### Claim 3 (depends on 2)

The power converter of claim 2, wherein the charge transferred from the capacitance of the active clamp circuit, that is injected into a primary winding, is previously transferred at or near a beginning of an off time of the power switch through the first diode from a leakage inductance of the power converter.

### Claim 4 (depends on 3)

The power converter of claim 3, wherein substantially no current is conducted through the clamp switch or the steering diode network after the charge from the leakage inductance has been transferred to the capacitance at or near the beginning of the off time of the power switch, and before the clamp switch is turned on near an end of the off time of the power switch to inject the charge stored in the capacitance into the primary winding.

### Claim 5 (depends on 1)

The power converter of claim 1, wherein the offset element comprises a Zener diode.

### Claim 6 (depends on 5)

The power converter of claim 5, wherein the steering diode network also comprises the Zener diode, an anode of the Zener diode is coupled to the clamp switch, and a cathode of the Zener diode is coupled to the power switch.

### Claim 7 (depends on 5)

The power converter of claim 5, wherein the Zener diode is coupled in series with a third diode, an anode of the third diode is coupled to the power switch, and a cathode of the third diode is coupled to the offset element.

### Claim 8 (depends on 1)

The power converter of claim 1, wherein the offset element comprises a resistance.

### Claim 9 (depends on 1)

The power converter of claim 1, wherein the offset element comprises a capacitance.

### Claim 10 (depends on 9)

The power converter of claim 9, wherein the capacitance of the offset element has a blocking voltage substantially equal to the product of a voltage across the clamp switch and the capacitance associated with the clamp switch divided by the sum of the capacitance associated with the clamp switch and the capacitance of the offset element.

### Claim 11 (depends on 9)

The power converter of claim 9, wherein a stored charge of the capacitance associated with the clamp switch is transferred to the capacitance of the offset element.

### Claim 12 (depends on 1)

The power converter of claim 1, wherein the clamp switch comprises a metal-oxide-semiconductor field-effect transistor.

### Claim 13 (depends on 1)

The power converter of claim 1, wherein the clamp switch comprises a cascode switch, the cascode switch comprising:
a normally-on device coupled to the capacitance; and
a normally-off device coupled to the normally-on device, the normally-off device coupled to the offset element.

### Claim 14 (depends on 1)

The power converter of claim 1, wherein the first controller comprises:
a regulation control circuit configured to generate the primary drive signal in response to a request signal including request events representative of a request to turn on the power switch to control a transfer of energy from the input of the power converter to the output of power converter; and
a clamp control circuit configured to generate a clamp drive signal in response to a signal representative of a determination to turn on the power switch, wherein the clamp drive signal is coupled to turn on the clamp switch for a first duration near an end of an off time of the power switch in response to the determination to turn on the power switch.

### Claim 15 (depends on 14)

The power converter of claim 14, wherein the clamp control circuit receives the request signal and the clamp control circuit is configured to generate the clamp drive signal in response to the request signal.

### Claim 16 (depends on 14)

The power converter of claim 14, wherein the regulation control circuit includes an enable circuit configured to generate an enable signal in response to the request signal and the clamp control circuit is further configured to generate the clamp drive signal in response to the request signal.

### Claim 17 (depends on 14)

The power converter of claim 14, wherein the regulation control circuit is further coupled to receive the clamp drive signal from the clamp control circuit, wherein the regulation control circuit further includes a delay circuit configured to output the primary drive signal in response to the clamp drive signal, wherein the delay circuit is further configured to delay turn-on of the power switch a second duration after the first duration to provide sufficient time for a parasitic capacitance of the power switch to be discharged into the energy transfer element before the power switch is turned on.

### Claim 18 (depends on 17)

The power converter of claim 17, wherein the regulation control circuit further includes a latch coupled between the clamp control circuit and the delay circuit, wherein the latch is coupled to be set in response to the clamp drive signal from the active clamp circuit to generate the primary drive signal received by the delay circuit.

### Claim 19 (depends on 18)

The power converter of claim 18, wherein the regulation control circuit is further coupled to receive a current sense signal representative of a switch current through the power switch, wherein the latch is coupled to be reset in response to the current sense signal that indicates that the switch current reaches a current limit to cause the primary drive signal to turn off the power switch.

### Claim 20 (depends on 18)

The power converter of claim 18, wherein the regulation control circuit further includes a comparator coupled to receive a current sense signal and a current limit signal, wherein an output of the comparator is coupled to reset the latch.

### Claim 21 (depends on 14)

The power converter of claim 14, wherein the clamp control circuit includes a monostable multivibrator coupled to generate the clamp drive signal in response to the signal representative of the determination to turn on the power switch, wherein the monostable multivibrator is coupled to output a pulse for the first duration in response to an edge in the signal representative of the determination to turn on the power switch.