Primary side control of primary resonant flyback converters

• US 10,218,256 B2
• Filed: 09/28/2017
• Issued: 02/26/2019
• Est. Priority Date: 07/28/2017
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Oh, InHwan
• Primary Examiner(s): Mehari, Yemane
• Application Number:
  US15/718,880
• Publication Number:
  US 20190036442A1
• Time in Patent Office: 516 Days
• Field of Search: 363 15, 363 17, 363 89
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• 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 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 1/083 for the ignition at the zero crossing of the voltage or the current
• CPC Class Codes: H02M 1/12 Arrangements for reducing harmonics from ac input or output
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 1/4241 using a resonant converter
• CPC Class Codes: H02M 1/4258 using a single converter stage both for correction of AC input power factor and generation of a regulated and galvanically isolated DC output voltage H02M1/4241 takes precedence
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 3/33576 having at least one active switching element at the secondary side of an isolation transformer
• 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 primary resonant flyback converter may include a primary winding, a resonant capacitor in series with the primary winding, a secondary winding magnetically coupled to the primary winding, and an output electrically coupled to the secondary winding. A main switch may be operated to energize the primary winding when closed and transfer energy stored in the primary winding to the secondary winding when open. An auxiliary switch may be configured to switch complimentarily to the main switch, thereby allowing a resonant current to circulate through the primary winding and capacitor. Switch timing may be controlled to produce a desired output voltage. The primary resonant flyback converter may include one or more of: (a) output voltage sensing across the resonant capacitor; (b) a full bridge switch configuration; and (c) lossless current sensing using a current sensing circuit coupled in parallel with the resonant capacitor.

Claims

1. A primary resonant flyback converter comprising:

a primary winding;

a secondary winding magnetically coupled to the primary winding and electrically coupled to an output rectifier, and an output terminal;

a resonant capacitor coupled in series with the primary winding;

a main switch configured to switch on to energize the primary winding and the resonant capacitor from a DC voltage bus and to switch off to transfer energy stored in the primary winding to the secondary winding;

an auxiliary switch configured to switch on during an off time of the main switch to allow a resonant current to circulate through the primary winding and the resonant capacitor; and

a control circuit configured to operate the main switch and the auxiliary switch to produce a desired voltage at the output terminal.

2. The primary resonant flyback converter of claim 1 wherein the control circuit is configured to operate the main switch and the auxiliary switch responsive to a voltage measured across the resonant capacitor.

3. The primary resonant flyback converter of claim 2 wherein:

the main switch comprises a high side main switch and a low side main switch;

the auxiliary switch comprises a high side auxiliary switch and a low side auxiliary switch;

wherein the switches are configured in a full bridge configuration with the primary winding and the resonant capacitor coupled between a junction of the high side main switch and the low side auxiliary switch and a junction of the high side auxiliary switch and the low side main switch.

4. The primary resonant flyback converter of claim 3 wherein the converter is configured to operate as a half bridge converter by opening the high side auxiliary switch and closing the low side main switch responsive to an input voltage into the converter.

5. The primary resonant flyback converter of claim 2 wherein the voltage measured across the resonant capacitor is an instantaneous voltage.

6. The primary resonant flyback converter of claim 2 wherein the voltage measured across the resonant capacitor is an average voltage.

7. The primary resonant flyback converter of claim 2 wherein the control circuit is further configured to implement output overvoltage protection based on the voltage measured across the resonant capacitor.

8. The primary resonant flyback converter of claim 2 wherein the control circuit is further configured to sense a current through the primary coil using a current sense circuit coupled in parallel with the resonant capacitor, the current sense circuit comprising a sense capacitor and at least one sense resistor.

9. A primary resonant flyback converter comprising:

a primary winding;

a secondary winding magnetically coupled to the primary winding and electrically coupled to a rectifier, and an output terminal;

a resonant capacitor coupled in series with the primary winding;

a main switch configured to switch on to energize the primary winding and the resonant capacitor from a DC voltage bus;

an auxiliary switch configured to switch on during an off time of the main switch to allow a resonant current to circulate through the primary winding and the resonant capacitor; and

a control circuit configured to operate the main switch and the auxiliary switch responsive to a sensed output voltage and further configured to sense a current through the primary coil using a current sense circuit coupled in parallel with the resonant capacitor, the current sense circuit comprising a sense capacitor and at least one sense resistor.

10. The primary resonant flyback converter of claim 9 wherein the sense capacitor has a lower capacitance than the resonant capacitor.

11. The primary resonant flyback converter of claim 9 wherein a cutoff frequency of the current sense circuit is configured to be higher than a switching frequency of the primary resonant flyback converter.

12. The primary resonant flyback converter of claim 9 wherein the control circuit is further configured to use the sensed current through the primary coil for overcurrent protection.

13. The primary resonant flyback converter of claim 9 wherein:

the main switch comprises a high side main switch and a low side main switch;

the auxiliary switch comprises a high side auxiliary switch and a low side auxiliary switch;

wherein the switches are configured in a full bridge configuration with the primary winding and the resonant capacitor coupled between a junction of the high side main switch and the low side auxiliary switch and a junction of the high side auxiliary switch and the low side main switch.

14. The primary resonant flyback converter of claim 13 wherein the converter is configured to operate as a half bridge converter by opening the high side auxiliary switch and closing the low side main switch responsive to an input voltage into the converter.

15. A method of operating a primary resonant flyback converter, the method comprising:

switching a main switch responsive to a sensed output voltage, wherein closing the main switch energizes a primary coil coupled in series with a resonant capacitor and opening the main switch transfers energy stored in the primary coil to a load electrically connected to a secondary coil magnetically coupled to the primary coil; and

switching an auxiliary switch complimentarily to the main switch, wherein closing the auxiliary switch allows a resonant current to circulate through the primary coil and the resonant capacitor;

wherein the sensed output voltage is a voltage across the resonant capacitor.

16. The method of claim 15 wherein the voltage across the resonant capacitor is an instantaneous voltage.

17. The method of claim 15 wherein the voltage across the resonant capacitor is an average voltage.

18. The method of claim 15 further comprising implementing output overvoltage protection for the primary resonant flyback converter responsive to the voltage across the resonant capacitor.

19. The method of claim 15 further comprising sensing a current through the primary coil using a current sense circuit coupled in parallel with the resonant capacitor, the current sense circuit comprising a sense capacitor and at least one sense resistor.

20. The method of claim 19 further comprising implementing overcurrent protection for the primary resonant flyback converter responsive to the sensed current.