# US 12,224,680 B2 · Active clamp flyback circuit

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- Number: US 12,224,680 B2
- Document ID: US12224680B2
- Status: Granted
- Kind: B2
- Application number: 18/163,481
- Filed: 2023-02-02
- Published: 2023-06-08
- Granted: 2025-02-11
- Earliest claimed: 2020-08-07
- Assignees: Huawei Digital Power Technologies Co., Ltd.
- Applicants: Huawei Digital Power Technologies Co., Ltd.
- Inventors: Jie Ren; Xue Zhang; Jun Yao
- Web page: https://patentgrep.com/patent/US12224680B2

## CPC

- H02M 3/33523: {with galvanic isolation between input and output of both the power stage and the feedback loop}
- H02M 7/4837: {Flying capacitor converters}
- 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 1/0095: {Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck}
- H02M 1/342: {Active non-dissipative snubbers}
- H02M 3/33571: {Half-bridge at primary side of an isolation transformer}
- H02M 7/5387: in a bridge configuration
- Y02B 70/10: Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
- 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)
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

An active clamp flyback circuit includes: a clamp capacitor that is connected to a primary-side winding of a transformer and that is configured to absorb leakage inductance energy of the primary-side winding; an auxiliary switching transistor that is configured to control the clamp capacitor to perform reverse excitation power charging on the primary-side winding by using the auxiliary switching transistor; a first diode, where the first diode is connected in series between the clamp capacitor and the auxiliary switching transistor; and a second diode, where the second diode is connected between the first diode and the clamp capacitor, and the second diode is connected in series between the clamp capacitor and a primary-side auxiliary winding.

## Claims

### Claim 1

An active clamp flyback converter, comprising:
a transformer comprising a primary-side winding, a primary-side auxiliary winding, and a secondary-side winding;
a primary power switching transistor, wherein the primary power switching transistor is connected to the primary-side winding, and the primary power switching transistor is configured to control the transformer to store energy by using the primary power switching transistor; and
an active clamp flyback circuit, wherein the active clamp flyback circuit is connected to the primary-side winding, the primary-side auxiliary winding, and the primary power switching transistor, and the active clamp flyback circuit is configured to absorb leakage inductance energy of the transformer, and
the active clamp flyback circuit comprises:
a clamp capacitor, wherein the clamp capacitor is connected to the primary-side winding and is configured to absorb leakage inductance energy of the primary-side winding;
an auxiliary switching transistor, wherein the auxiliary switching transistor is configured to control the clamp capacitor to perform reverse excitation power charging on the primary-side winding by using the auxiliary switching transistor;
a first diode, wherein the first diode is connected in series between the clamp capacitor and the auxiliary switching transistor; and
a second diode, wherein the second diode is connected between the first diode and the clamp capacitor, and the second diode is connected in series between the clamp capacitor and the primary-side auxiliary winding, and
the primary-side winding is connected between the primary power switching transistor and the auxiliary switching transistor, and an electrical connection exists between the primary power switching transistor and the auxiliary switching transistor to form a half-bridge structure.

### Claim 2 (depends on 1)

The active clamp flyback converter according to claim 1, wherein the primary power switching transistor and the auxiliary switching transistor are both switching transistors, the switching transistor comprises a control electrode, a first transmission electrode, and a second transmission electrode, the switching transistor is configured to controls, through controlling a forward voltage from the control electrode to the first transmission electrode, conduction and cut-off of a forward current flowing from the second transmission electrode to the first transmission electrode, and the first transmission electrode of the auxiliary switching transistor is electrically connected to the second transmission electrode of the primary power switching transistor to form the half-bridge structure.

### Claim 3 (depends on 2)

The active clamp flyback converter according to claim 2, wherein an anode of the first diode is connected to the clamp capacitor, a cathode of the first diode is connected to the second transmission electrode of the auxiliary switching transistor, and the first diode is configured to block flowing of a reverse current relative to the first diode from the auxiliary switching transistor to the clamp capacitor.

### Claim 4 (depends on 3)

The active clamp flyback converter according to claim 3, wherein an anode of the second diode is connected to the primary-side auxiliary winding, a cathode of the second diode is connected to the clamp capacitor, and the second diode is configured to block flowing of a reverse current relative to the second diode from the clamp capacitor to the primary-side auxiliary winding.

### Claim 5 (depends on 4)

The active clamp flyback converter according to claim 4, wherein,
when the primary power switching transistor and the auxiliary switching transistor are both in an off state, the clamp capacitor is configured to absorb leakage inductance energy of the primary-side winding and the primary-side auxiliary winding by using the second diode, and ends with the same name of the primary-side winding and the primary-side auxiliary winding are connected in series, so that a clamp voltage generated on the clamp capacitor by the primary-side winding is offset by a clamp voltage generated on the clamp capacitor by the primary-side auxiliary winding.

### Claim 6 (depends on 5)

The active clamp flyback converter according to claim 5, wherein,
when the primary power switching transistor is in the off state and the auxiliary switching transistor is in an on state, the clamp capacitor is configured to performs reverse excitation power charging on the primary-side winding by using the first diode and the auxiliary switching transistor, and the second diode is configured to blocks reverse excitation power charging performed on the primary-side auxiliary winding by the clamp capacitor by using the second diode.

### Claim 7 (depends on 6)

The active clamp flyback converter according to claim 6, wherein an amplitude of an excitation voltage applied to the primary-side winding by the clamp capacitor is adjusted through adjusting a turn quantity ratio of the primary-side auxiliary winding relative to the primary-side winding.

### Claim 8 (depends on 4)

The active clamp flyback converter according to claim 4, wherein the active clamp flyback converter further comprises a controller, the controller is connected to the primary power switching transistor and the secondary switching transistor, and the controller is configured to perform the following operations:
switching the primary power switching transistor to an on state to allow a current flow through a primary power loop, wherein the primary power loop comprises the primary-side winding and the primary power switching transistor;
switching the primary power switching transistor to an off state, and switching the auxiliary switching transistor to the off state, to allow a current flow through a clamp loop and allow the clamp capacitor to absorb leakage inductance energy of the transformer through the clamp loop, wherein the clamp loop comprises the primary-side winding, the primary-side auxiliary winding, the second diode, and the clamp capacitor;
switching the primary power switching transistor to the off state, and switching the auxiliary switching transistor to an on state, to allow a current flow through a reverse excitation loop and allow the clamp capacitor to perform reverse excitation power charging on the transformer through the reverse excitation loop, wherein the reverse excitation loop comprises the clamp capacitor, the first diode, the auxiliary switching transistor, and the primary-side winding; and
switching the primary power switching transistor to the on state based on a reverse excitation power charging degree of the clamp capacitor for the transformer, to implement zero voltage switching.

### Claim 9 (depends on 2)

The active clamp flyback converter according to claim 2, wherein a cathode of the first diode is connected to the clamp capacitor, an anode of the first diode is connected to the first transmission electrode of the auxiliary switching transistor and the second transmission electrode of the primary power switching transistor, and the first diode is configured to block flowing of a reverse current relative to the first diode from the clamp capacitor to the primary-side winding.

### Claim 10 (depends on 9)

The active clamp flyback converter according to claim 9, wherein a cathode of the second diode is connected to the primary-side auxiliary winding, an anode of the second diode is connected to the clamp capacitor and the cathode of the first diode, and the second diode is configured to block flowing of a reverse current relative to the second diode from the primary-side auxiliary winding to the clamp capacitor.

### Claim 11 (depends on 10)

The active clamp flyback converter according to claim 10, wherein,
when the primary power switching transistor and the auxiliary switching transistor are both in an off state, the clamp capacitor is configured to absorb leakage inductance energy of the primary-side winding by using the first diode, and the second diode is configured to block absorbing of leakage inductance energy of the primary-side auxiliary winding by the clamp capacitor by using the second diode.

### Claim 12 (depends on 11)

The active clamp flyback converter according to claim 11, wherein,
when the primary power switching transistor is in the off state and the auxiliary switching transistor is in an on state, the clamp capacitor is configured to performs reverse excitation power charging on the primary-side auxiliary winding by using the second diode, the clamp capacitor is configured to perform reverse excitation power charging on the primary-side winding by using the second diode and the auxiliary switching transistor, and the first diode is configured to block a current for the reverse excitation power charging performed on the primary-side winding by the clamp capacitor so that the current does not pass through the primary-side auxiliary winding.

### Claim 13 (depends on 12)

The active clamp flyback converter according to claim 12, wherein an amplitude of an excitation voltage applied to the primary-side winding by the clamp capacitor is adjusted through adjusting a turn quantity ratio of the primary-side auxiliary winding relative to the primary-side winding.

### Claim 14 (depends on 10)

The active clamp flyback converter according to claim 10, wherein the active clamp flyback converter further comprises a controller, the controller is connected to the primary power switching transistor and the secondary switching transistor, and the controller is configured to perform the following operations:
switching the primary power switching transistor to an on state to allow a current flow through a primary power loop, wherein the primary power loop comprises the primary-side winding and the primary power switching transistor;
switching the primary power switching transistor to an off state, and switching the auxiliary switching transistor to the off state, to allow a current flow through a clamp loop and allow the clamp capacitor to absorb leakage inductance energy of the transformer through the clamp loop, wherein the clamp loop comprises the primary-side winding, the first diode, and the clamp capacitor;
switching the primary power switching transistor to the off state, and switching the auxiliary switching transistor to the on state, to allow a current flow through a reverse excitation loop and allow the clamp capacitor to perform reverse excitation power charging on the transformer through the reverse excitation loop, wherein the reverse excitation loop comprises the clamp capacitor, the second diode, the primary-side auxiliary winding, the auxiliary switching transistor, and the primary-side winding; and
switching the primary power switching transistor to the on state based on a reverse excitation power charging degree of the clamp capacitor for the transformer, to implement zero voltage switching.

### Claim 15 (depends on 2)

The active clamp flyback converter according to claim 2, wherein the switching transistor is a MOSFET, and the control electrode, the first transmission electrode, and the second transmission electrode of the switching transistor respectively correspond to a gate, a source, and a drain of the MOSFET.

### Claim 16 (depends on 2)

The active clamp flyback converter according to claim 2, wherein the switching transistor is an IGBT, and the control electrode, the first transmission electrode, and the second transmission electrode of the switching transistor respectively correspond to a base, an emitter, and a collector of the IGBT.

### Claim 17 (depends on 2)

The active clamp flyback converter according to claim 2, wherein the switching transistor is a HEMT, and the control electrode, the first transmission electrode, and the second transmission electrode of the switching transistor respectively correspond to a gate, a source, and a drain of the HEMT.

### Claim 18 (depends on 17)

The active clamp flyback converter according to claim 17, wherein the HEMT is a GaN HEMT.

### Claim 19

A switch-mode power supply, wherein the switch-mode power supply comprises an active clamp flyback converter, wherein the active clamp flyback converter comprises:
a transformer, wherein the transformer comprises a primary-side winding, a primary-side auxiliary winding, and a secondary-side winding;
a primary power switching transistor, wherein the primary power switching transistor is connected to the primary-side winding, and the primary power switching transistor is configured to control the transformer to store energy by using the primary power switching transistor; and
an active clamp flyback circuit, wherein the active clamp flyback circuit is connected to the primary-side winding, the primary-side auxiliary winding, and the primary power switching transistor, and the active clamp flyback circuit is configured to absorb leakage inductance energy of the transformer, and
the active clamp flyback circuit comprises:
a clamp capacitor, wherein the clamp capacitor is connected to the primary-side winding and is configured to absorb leakage inductance energy of the primary-side winding;
an auxiliary switching transistor, wherein the auxiliary switching transistor is configured to control the clamp capacitor to perform reverse excitation power charging on the primary-side winding by using the auxiliary switching transistor;
a first diode, wherein the first diode is connected in series between the clamp capacitor and the auxiliary switching transistor; and
a second diode, wherein the second diode is connected between the first diode and the clamp capacitor, and the second diode is connected in series between the clamp capacitor and the primary-side auxiliary winding, and
the primary-side winding is connected between the primary power switching transistor and the auxiliary switching transistor, and an electrical connection exists between the primary power switching transistor and the auxiliary switching transistor to form a half-bridge structure.