# US 12,009,753 B2 · Half-bridge flyback power converter and control method thereof

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- Number: US 12,009,753 B2
- Document ID: US12009753B2
- Status: Granted
- Kind: B2
- Application number: 17/673,298
- Filed: 2022-02-16
- Published: 2022-08-25
- Granted: 2024-06-11
- Earliest claimed: 2021-02-25
- Assignees: Richtek Technology Corporation
- Applicants: Richtek Technology Corporation
- Inventors: Ta-Yung Yang; Ying-Chieh Su; Yu-Chang Chen
- Web page: https://patentgrep.com/patent/US12009753B2

## CPC

- H02M 3/01: {Resonant DC/DC converters}
- H02M 3/33571: {Half-bridge at primary side of an isolation transformer}
- H02M 1/0035: {using burst mode control}
- 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 1/083: {for the ignition at the zero crossing of the voltage or the current}
- H02M 3/33523: {with galvanic isolation between input and output of both the power stage and the feedback loop}
- H02M 3/33592: {having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer}
- H02M 1/0009: {Devices or circuits for detecting current in a converter}
- 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

A half-bridge flyback power converter: a first transistor, a second transistor and a third transistor which form a half-bridge circuit. The first transistor is turned on for generating a negative circulated current for achieving zero voltage switching of the second transistor. The second transistor is turned on for magnetizing a transformer. The third transistor is turned on during a demagnetized time period to generate an output voltage. The physical size of the first transistor is smaller than physical size of the third transistor.

## Claims

### Claim 1

A half-bridge flyback power converter, comprising:
a first transistor controlled by a first signal;
a second transistor controlled by a second signal;
a third transistor controlled by a third signal, wherein the first transistor, the second transistor and the third transistor are directly connected to a switching node and configured to form a half-bridge circuit for switching a resonant tank which is electrically connected to the switching node, wherein the first transistor and the third transistor are directly connected in parallel and independently controllable, wherein the resonant tank includes a resonant capacitor and a primary winding of a transformer of the half-bridge flyback power converter, wherein the resonant capacitor and the primary winding are electrically connected in series from the switching node; and
a switching control circuit, configured to operably generate the first signal according to an input voltage of the flyback power converter, and generate the third signal according to an output voltage of the flyback power converter, and generate the second signal according to a feedback signal related to the output voltage of the half-bridge flyback power converter;
during a discontinuous conduction mode (DCM) operation, the switching control circuit operating in a first switching cycle controls the first signal to turn on the first transistor for a first period, wherein after the first period, the switching control circuit controls the first signal, the second signal and the third signal to turn off the first transistor, the second transistor and the third transistor for a first off-time period, wherein after the first off-time period, the switching control circuit controls the second signal to turn on the second transistor for a second period, wherein after the second period, the switching control circuit controls the first signal, the second signal and the third signal to turn off the first transistor, the second transistor and the third transistor for a second off-time period, wherein after the second off-time period, the switching control circuit controls the third signal to turn on the third transistor for a third period, wherein after the third period, the switching control circuit controls the first signal, the second signal and the third signal to turn off the first transistor, the second transistor and the third transistor for a third off-time period;
wherein the first transistor and the third transistor are configured respectively as an auxiliary low-side transistor and a primary low-side transistor of the half-bridge flyback power converter, wherein the auxiliary low-side transistor and the primary low-side transistor are directly connected in parallel between the switching node and a ground potential and are independently controllable, and the second transistor is configured as a high-side transistor of the half-bridge flyback power converter;
wherein the half-bridge flyback power converter further comprising a timer for timing the third off-time period; and
wherein the third off-time period of the timer is increased in response to the decrease of output power of the half-bridge flyback power converter.

### Claim 2 (depends on 1)

The half-bridge flyback power converter of claim 1, wherein the first transistor is turned on to generate a circulated current for achieving ZVS (Zero Voltage Switching) for the second transistor during the DCM operation.

### Claim 3 (depends on 1)

The half-bridge flyback power converter of claim 1, wherein the second transistor is turned on to magnetize the transformer of the flyback converter.

### Claim 4 (depends on 3)

The half-bridge flyback power converter of claim 3, wherein the third transistor is turned on during a demagnetizing period of the transformer.

### Claim 5 (depends on 1)

The half-bridge flyback power converter of claim 1, wherein a physical size of the first transistor is smaller than a physical size of the third transistor.

### Claim 6 (depends on 1)

The half-bridge flyback power converter of claim 1, wherein
an amplitude of the first signal is lower than an amplitude of the third signal; and/or
a gate related maximum rating of the first transistor is lower than a gate related maximum rating of the third transistor.

### Claim 7

A control method for controlling a half-bridge flyback power converter, wherein the half-bridge flyback power converter includes a first transistor, a second transistor, and a third transistor, wherein the first transistor, the second transistor and the third transistor are directly connected to a switching node and configured to form a half-bridge circuit for switching a resonant tank which is electrically connected to the switching node, wherein the first transistor and the third transistor are directly connected in parallel and independently controllable, wherein the resonant tank includes a resonant capacitor and a primary winding of a transformer of the half-bridge flyback power converter, wherein the resonant capacitor and the primary winding are electrically connected in series from the switching node; the control method comprising:
generating a first signal for driving the first transistor according to an input voltage of the half-bridge flyback power converter;
generating a second signal for driving the second transistor according to a feedback signal related to an output voltage of the half-bridge flyback power converter; and
generating a third signal for driving the third transistor according to the output voltage;
wherein the step of driving the first transistor, the second transistor, and the third transistor includes:
during a discontinuous conduction mode (DCM) operation, controlling the first transistor to turn on for a first period;
after the first period, controlling the first transistor, the second transistor and the third transistor to turn off for a first off-time period;
after the first off-time period, controlling the second transistor to turn on for a second period;
after the second period, controlling the first transistor, the second transistor and the third transistor to turn off for a second off-time period;
after the second off-time period, controlling the third transistor to turned on for a third period; and
after the third period, controlling the first transistor, the second transistor and the third transistor to turn off for a third off-time period;
wherein the first transistor and the third transistor are configured respectively as an auxiliary low-side transistor and a primary low-side transistor of the half-bridge flyback power converter, wherein the auxiliary low-side transistor and the primary low-side transistor are directly connected in parallel between the switching node and a ground potential and are independently controllable, and the second transistor is configured as a high-side transistor of the half-bridge flyback power converter; and
wherein the control method further comprising:
increasing the third off-time period in response to the decrease of output power of the half-bridge flyback power converter.

### Claim 8 (depends on 7)

The control method of claim 7, further comprising:
generating a circulated current by turning on the first transistor to achieve ZVS for the second transistor during the DCM operation.

### Claim 9 (depends on 7)

The control method of claim 7, wherein the second transistor is turned on to magnetize the transformer.

### Claim 10 (depends on 7)

The control method of claim 7, wherein the third transistor is turned on during a demagnetizing period of the transformer.

### Claim 11 (depends on 7)

The control method of claim 7, wherein a physical size of the first transistor is smaller than a physical size of the third transistor.

### Claim 12 (depends on 7)

The control method of claim 7, wherein an amplitude of the first signal is lower than an amplitude of the third signal.