CONTROL DEVICE AND CONTROL METHOD

• US 20180294734A1
• Filed: 04/04/2018
• Published: 10/11/2018
• Est. Priority Date: 04/10/2017
• Status: Active Grant

• Current Assignee: Delta Electronics Shanghai Company Limited (Delta Electronics Incorporated)
• Original Assignee: Delta Electronics Shanghai Company Limited (Delta Electronics Incorporated)
• Inventors: SONG, Haibin, ZHANG, Jinfa, XU, Daofei
• Granted Patent: US 10,333,417 B2
• Time in Patent Office: Days
• CPC Class Codes: 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
• CPC Class Codes: H02M 1/083 for the ignition at the zero crossing of the voltage or the current
• CPC Class Codes: H02M 3/335 using semiconductor devices only
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H02M 3/33592 having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
• CPC Class Codes: 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

Abstract

A control device, which is applied to a flyback converter including an auxiliary switch, includes: an on-time setter, configured to set an on-time threshold according to a reference value and an output voltage of the flyback converter; and an on-time controller, configured to output a control signal to turn on the auxiliary switch, and turn off the auxiliary switch when on-time of the auxiliary switch reaches the on-time threshold. According to the present disclosure, it is able to achieve zero voltage switching of a primary-side switch of the flyback converter with variable outputs.

Claims

1. A control device, applied to a flyback converter, the flyback converter comprising an auxiliary switch, the control device comprising:

an on-time setter, configured to set an on-time threshold according to a reference value and an output voltage of the flyback converter; and

an on-time controller, configured to output a control signal to turn on the auxiliary switch, and to turn off the auxiliary switch when on-time of the auxiliary switch reaches the on-time threshold.

2. The control device according to claim 1, wherein the flyback converter comprises a Resistor Capacitor Diode (RCD) clamp flyback converter or an active clamp flyback converter.

3. The control device according to claim 1, wherein the auxiliary switch comprises any one selected from a group comprising a synchronous rectifier, a clamp switch, a switch connected in parallel with a secondary-side rectifier of the flyback converter, and a switch connected in series with an auxiliary winding of the flyback converter.

4. The control device according to claim 1, wherein the on-time controller is configured to output the control signal according to a timing start signal.

5. The control device according to claim 4, wherein the on-time controller comprises a timer and an auxiliary switch controller;

wherein the timer is configured to receive the timing start signal, and generate a timing signal when the timer is started according to the timing start signal; and

wherein the auxiliary switch controller is configured to receive the timing signal, and generate the control signal according to the timing signal.

6. The control device according to claim 5, wherein the auxiliary switch controller is configured to turn on the auxiliary switch according to the timing start signal.

7. The control device according to claim 5, wherein when the timing signal is greater than or equal to the on-time threshold, the auxiliary switch controller turns off the auxiliary switch.

8. The control device according to claim 5, wherein the timer is further configured to reset the timer according to a reset signal.

9. The control device according to claim 5, wherein

in a discontinuous current mode of the flyback converter, the timing start signal is obtained by detecting a turn-on signal of the auxiliary switch;

and

in a discontinuous current mode boundary of the flyback converter, the timing start signal is obtained by detecting a zero crossing point of the negative magnetizing current in the flyback converter.

10. The control device according to claim 8, wherein the reset signal is obtained by detecting a turn-off signal of the auxiliary switch.

11. The control device according to claim 1, wherein the on-time setter comprises:

a reference calculator, configured to generate the reference value; and

an on-time calculator, configured to obtain the on-time threshold according to the reference value and the output voltage of the flyback converter.

12. The control device according to claim 11, wherein the reference calculator is configured to set the reference value according to an input voltage of the flyback converter;

or

the reference calculator is configured to set the reference value according to an input voltage of the flyback converter and an output voltage of the flyback converter.

13. The control device according to claim 1, wherein an output voltage of the flyback converter is variable.

14. A switching power supply, comprising the control device applied to a flyback converter comprising an auxiliary switch, wherein the control device comprises:

an on-time setter, configured to set an on-time threshold according to a reference value and an output voltage of the flyback converter; and

an on-time controller, configured to output a control signal to turn on the auxiliary switch, and to turn off the auxiliary switch when on-time of the auxiliary switch reaches the on-time threshold.

15. A control method, applied to a flyback converter, the flyback converter comprising an auxiliary switch, the control method comprising steps:

(a) detecting an output voltage of the flyback converter, and setting an on-time threshold according to the output voltage and a reference value; and

(b) turning on the auxiliary switch according to a control signal, and turning off the auxiliary switch when on-time of the auxiliary switch reaches the on-time threshold.

16. The control method according to claim 15, wherein the flyback converter comprises a Resistor Capacitor Diode (RCD) clamp flyback converter or an active clamp flyback converter.

17. The control method according to claim 15, wherein the auxiliary switch comprises any one selected from a group comprising a synchronous rectifier, a clamp switch, a switch connected in parallel with a secondary-side rectifier of the flyback converter, and a switch connected in series with an auxiliary winding of the flyback converter.

18. The control method according to claim 17, wherein the Step (b) comprises:

outputting the control signal according to a timing start signal.

19. The control method according to claim 18, wherein the Step (b) comprises:

generating a timing signal when starting a timer according to a timing start signal; and

generating the control signal according to the timing signal.

20. The control method according to claim 18, wherein the auxiliary switch is turned on according to the timing start signal.

21. The control method according to claim 18, wherein the auxiliary switch is turned off when the timing signal is greater than or equal to the on-time threshold.

22. The control method according to claim 19, wherein the Step (b) further comprises:

resetting the timer according to a reset signal.

23. The control method according to claim 18, wherein in a discontinuous current mode of the flyback converter, the timing start signal is obtained by detecting a turn-on signal of the auxiliary switch;

and in a discontinuous current mode boundary of the flyback converter, the timing start signal is obtained by detecting a zero crossing point of the negative magnetizing current in the flyback converter.

24. The control method according to claim 22, wherein the reset signal is obtained by detecting a turn-off signal of the auxiliary switch.

25. The control method according to claim 15, wherein the Step (a) comprises:

generating the on-time threshold according to the output voltage and the reference value through a division operation.

26. The control method according to claim 15, further comprising:

(c) after the auxiliary switch is turned off, achieving zero voltage switching of a primary-side power switch of the flyback converter by resonance of an magnetizing inductor and a parasitic capacitor in the flyback converter.

27. The control method according to claim 15, wherein the Step (a) further comprises:

setting the reference value according to an input voltage of the flyback converter;

or

setting the reference value according to an input voltage of the flyback converter and an output voltage of the flyback converter.

28. The control method according to claim 27, wherein the Step (a) further comprises:

setting the negative magnetizing current reference value according to a maximum value of the input voltage of the flyback converter.

29. The control method according to claim 28, wherein an output voltage of the flyback converter is variable.