Flyback power converter and control method thereof

Patent metadata

Field	Value
Publication number	US-12542494-B2
Application number	US-202318381584-A
Country	US
Kind code	B2
Filing date	Oct 18, 2023
Priority date	Nov 11, 2022
Publication date	Feb 3, 2026
Grant date	Feb 3, 2026

Abstract

A control method for a flyback power converter is provided. Firstly, a flyback power converter is provided. The flyback power converter includes a transformer, a leakage inductance energy recovery circuit and a control unit. Then, a delayed turn-off time period is defined by the control unit. Then, a detection signal related to a current flowing through the leakage inductance energy recovery circuit is detected. If the detection signal is greater than or equal to a first set value, a switch element of the leakage inductance energy recovery circuit is turned on. If the detection signal is lower than or equal to a second set value, the second switch element is turned off after the delayed turn-off time period.

First claim

What is claimed is:

1 . A control method for a flyback power converter, the control method comprising steps of:
(a) providing the flyback power converter, wherein the flyback power converter comprises a transformer, a leakage inductance energy recovery circuit, a first switch element and a control unit, wherein the leakage inductance energy recovery circuit comprises a first capacitor and a second switch element, wherein a first terminal of the first capacitor is electrically connected with a first terminal of a primary winding of the transformer, the second switch element is electrically connected between a second terminal of the first capacitor and a second terminal of the primary winding, the control unit is electrically connected with a control terminal of the second switch element, and a first terminal of the first switch element is electrically connected with a second terminal of the primary winding; (b) defining a delayed turn-off time period by the control unit; (c) the control unit detecting a detection signal, wherein the detection signal is related to a current flowing through the leakage inductance energy recovery circuit; (d) determining whether the detection signal is greater than or equal to a first set value, wherein when a determining condition of the step (d) is satisfied, a step (e) is performed, wherein when the determining condition of the step (d) is not satisfied, the step (c) is performed again; (e) turning on the second switch element under control of the control unit; (f) determining whether the detection signal is lower than or equal to a second set value, wherein when a determining condition of the step (f) is satisfied, a step (g) is performed, wherein when the determining condition of the step (f) is not satisfied, the step (e) is performed again; and (g) turning off the second switch element under control of the control unit after the delayed turn-off time period.

2 . The control method according to claim 1 , wherein the flyback power converter comprises a resonant circuit, the resonant circuit comprises a leakage inductor of the transformer and the first capacitor, the resonant circuit has a resonant cycle, and the delayed turn-on time period is in a range between ¼ and ½ of the resonant cycle.

3 . The control method according to claim 1 , wherein a gate-source charge of the second switch element is lower than 10 nC.

4 . The control method according to claim 1 , wherein the leakage inductance energy recovery circuit further comprises a second resistor, wherein a first terminal of the second resistor is electrically connected with a second terminal of the second switch element and the control unit, and a second terminal of the second resistor is electrically connected with the second terminal of the primary winding and the control unit.

5 . The control method according to claim 4 , wherein the detection signal is a current value of a current flowing through the second resistor, wherein a direction of the current from the second terminal of the second resistor to the first terminal of the second resistor is defined as a forward direction, the first set value is a first current set value, and the second set value is a second current set value.

6 . The control method according to claim 5 , wherein the control unit comprises a first pin, a second pin and a third pin, wherein the first pin is electrically connected with the first terminal of the second resistor, the second pin is electrically connected with the second terminal of the second resistor, and the third pin is electrically connected with the control terminal of the second switch element.

7 . The control method according to claim 6 , wherein the flyback power converter further comprises a bootstrap circuit, and the bootstrap circuit comprises a diode and a bootstrap capacitor, wherein an anode terminal of the diode is electrically connected with a voltage source, a cathode terminal of the diode is electrically connected with a first terminal of the bootstrap capacitor, and a second terminal of the bootstrap capacitor is electrically connected with the first pin.

8 . The control method according to claim 5 , wherein the first current set value is in a range between 0 A and 0.5 A, and the second current set value is in a range between −0.5 A and 0 A.

9 . The control method according to claim 4 , wherein a resistance of the second resistor is in a range between 0.5 ohm˜100 ohm.

10 . The control method according to claim 1 , wherein the control unit is further connected with the first terminal and the second terminal of the second switch element, and the detection signal is voltage difference between the second terminal and the first terminal of the second switch element, wherein the first set value is a first voltage set value, and the second set value is a second voltage set value.

11 . The control method according to claim 10 , wherein the first voltage set value is in a range between 0V and 1V, and the second voltage set value is in a range between −1V and 0V.

12 . The control method according to claim 10 , wherein the control unit comprises a first pin, a second pin and a third pin, wherein the first pin is electrically connected with the second terminal of the second switch element, the second pin is electrically connected with the first terminal of the second switch element, and the third pin is electrically connected with the control terminal of the second switch element.

13 . The control method according to claim 1 , wherein the delayed turn-off time period is defined by the control unit, or the delayed turn-off time period is determined according to a resistance of a first resistor, wherein the first resistor is electrically connected between the control unit and the second switch element.

14 . A flyback power converter, comprising:
a transformer comprising a primary winding and a secondary winding, wherein a first terminal of the primary winding is electrically connected with a positive input terminal; a first switch element, wherein a first terminal of the first switch element is electrically connected with a second terminal of the primary winding, and a second terminal of the first switch element is electrically connected with a negative input terminal; a leakage inductance energy recovery circuit comprising a first capacitor, a second resistor and a second switch element, wherein a first terminal of the first capacitor is electrically connected with the first terminal of the primary winding, a first terminal of the second switch element is electrically connected with a second terminal of the first capacitor, a second terminal of the second switch element is electrically connected with a first terminal of the second resistor, and a second terminal of the second resistor is electrically connected with the second terminal of the primary winding; and a control unit electrically connected with the first terminal and the second terminal of the second resistor and a control terminal of the second switch element, wherein a delayed turn-off time period is defined by the control unit or defined according to a first resistor, wherein a direction of a current flowing through the second resistor from the second terminal of the second resistor to the first terminal of the second resistor is defined as a forward direction, wherein when a current value of the current flowing through the second resistor is greater than or equal to a first current set value, the second switch element is turned on under control of the control unit, wherein when the current value of the current flowing through the second resistor is lower than or equal to

Assignees

• Delta Electronics Shanghai Co

Inventors

• Ma Kehua
• Xu Daofei
• Zhang Haitao

Classifications

• H02M3/33523

  with galvanic isolation between input and output of both the power stage and the feedback loop · CPC title

• H02M3/33507

  with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence) · CPC title

• H02M3/33576 Primary

  having at least one active switching element at the secondary side of an isolation transformer · CPC title

• Y02B70/10

  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 · CPC title

• H02M1/0009

  Devices or circuits for detecting current in a converter · CPC title