# US 10,770,965 B2 · Control of series-parallel mode (SPM) clamped flyback converter

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- Number: US 10,770,965 B2
- Document ID: US10770965B2
- Status: Granted
- Kind: B2
- Application number: 16/365,100
- Filed: 2019-03-26
- Published: 2019-07-18
- Granted: 2020-09-08
- Earliest claimed: 2015-06-15
- Assignees: Apple Inc.
- Applicants: Apple Inc.
- Inventors: Marco A. Davila; Joao L. Andres; Bogdan T. Bucheru; Vijay Phadke
- Web page: https://patentgrep.com/patent/US10770965B2

## CPC

- H02M 1/34: Snubber circuits
- H02M 1/08: Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M 3/33569: {having several active switching elements (H02M3/3353 takes precedence)}
- H02M 1/342: {Active non-dissipative snubbers}
- H02M 1/346: {Passive non-dissipative snubbers}
- H02M 3/01: {Resonant DC/DC converters}
- H02M 3/33576: {having at least one active switching element at the secondary side of an isolation transformer}
- 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

This disclosure describes a flyback converter with a series-parallel mode (SPM) active clamp. The active clamp, coupled in parallel with the primary coil, may include a clamp switch, two or more snubber capacitors, and associated diodes. The active clamp may be configured to absorb and retain the leakage energy from the leakage inductance of the flyback converter. The clamp switch may be turned on selectively as the primary switch approaches one of a plurality peak values to adjust frequencies of the switching devices. With the active clamp circuit, the flyback converter may first re-capture the leakage energy in the active clamp circuit and then recover it back to the power source.

## Claims

### Claim 1

A power conversion apparatus, comprising:
a primary coil configured to receive an input voltage;
a secondary coil electromagnetically coupled to the primary coil and configured to provide an output voltage;
a first switch coupled to the primary coil and configured to control a flow of current through the primary coil;
a second switch configured to control a flow of current through an active clamp circuit, the active clamp circuit coupled in parallel with the primary coil and configured to absorb a leakage energy from a leakage inductance associated with the primary coil and the secondary coil, the active clamp circuit comprising a first capacitor and a second capacitor; and
a controller coupled to the first switch and the second switch, the controller configured to:
turn the first switch on, so as to store energy in the primary coil;
turn the first switch off, so as to charge the first and the second capacitors in series;
turn the second switch on when a voltage across the first switch approaches a peak value, so as to discharge the first and the second capacitors in parallel; and
turn the second switch off when at least one of: a voltage across the first capacitor and a voltage across the second capacitor, falls to a predetermined voltage level.

### Claim 2 (depends on 1)

The power conversion apparatus of claim 1, wherein the first switch is turned on when a current is flowing through a body diode of the first switch or when the voltage across the first switch is determined to reach a minimum non-zero voltage.

### Claim 3 (depends on 1)

The power conversion apparatus of claim 1, wherein the first capacitor and the second capacitor have equivalent capacitance.

### Claim 4 (depends on 1)

The power conversion apparatus of claim 1, wherein the active clamp circuit further comprises a first diode.

### Claim 5 (depends on 4)

The power conversion apparatus of claim 4, wherein the first diode is coupled in series with the first capacitor and the second capacitor to block any reverse current from discharging the first capacitor and the second capacitor in series.

### Claim 6 (depends on 4)

The power conversion apparatus of claim 4, wherein the active clamp circuit further comprises a second diode and a third diode.

### Claim 7 (depends on 6)

The power conversion apparatus of claim 6,
wherein the second diode is coupled in parallel with the first capacitor and the first diode,
wherein the third diode is coupled in parallel with the second capacitor and the first diode, and
wherein the second diode and the third diode are configured to allow a flow of reverse current to discharge the first capacitor and the second capacitor in parallel.

### Claim 8 (depends on 1)

The power conversion apparatus of claim 1,
wherein the voltage across the first switch, after the first switch is turned off and before the second switch is turned on, represents a sinusoidal voltage that includes a plurality of peak values, and
wherein the second switch is turned on when the voltage across the first switch approaches one of the plurality of peak values.

### Claim 9

A method for operating a power conversion apparatus, comprising:
receiving an input voltage at a primary coil;
providing an output voltage at a secondary coil, the secondary coil electromagnetically coupled to the primary coil;
controlling a flow of current through the primary coil by using a first switch; and
controlling a flow of current through an active clamp circuit by using a second switch, the active clamp circuit coupled in parallel with the primary coil and configured to absorb a leakage energy from a leakage inductance associated with the primary coil and the secondary coil, the active clamp circuit comprising a first capacitor and a secondary capacitor,
wherein the first switch and second switch are controlled by a controller, the controller configured to:
turn the first switch on, so as to store energy in the primary coil;
turn the first switch off, so as to charge the first and the second capacitors in series;
turn the second switch on when a voltage across the first switch approaches a peak value, so as to discharge the first and the second capacitors in parallel; and
turn the second switch off when at least one of: a voltage across the first capacitor and a voltage across the second capacitor, falls to a predetermined voltage level.

### Claim 10 (depends on 9)

The method of claim 9, wherein the first switch is turned on when a current is flowing through a body diode of the first switch or when the voltage across the first switch is determined to reach a minimum non-zero voltage.

### Claim 11 (depends on 9)

The method of claim 9, wherein the first capacitor and the second capacitor have equivalent capacitance.

### Claim 12 (depends on 9)

The method of claim 9, wherein the active clamp circuit further comprises a first diode.

### Claim 13 (depends on 12)

The method of claim 12, wherein the first diode is coupled in series with the first capacitor and the second capacitor to block any reverse current from discharging the first capacitor and the second capacitor in series.

### Claim 14 (depends on 12)

The method of claim 12, wherein the active clamp circuit further comprises a second diode and a third diode.

### Claim 15 (depends on 14)

The method of claim 14,
wherein the second diode is coupled in parallel with the first capacitor and the first diode,
wherein the third diode is coupled in parallel with the second capacitor and the first diode, and
wherein the second diode and the third diode are configured to allow a flow of reverse current to discharge the first capacitor and the second capacitor in parallel.

### Claim 16 (depends on 9)

The method of claim 9,
wherein the voltage across the first switch, after the first switch is turned off and before the second switch is turned on, represent a sinusoidal voltage that includes a plurality of peak values, and
wherein the second switch is turned on when the voltage across the first switch approaches one of the plurality of peak values.

### Claim 17

A power converter, comprising:
a primary coil coupled in series with a first switch, the primary coil configured to receive an input voltage;
a secondary coil electromagnetically coupled to the primary coil, the secondary configured to provide an output voltage;
an active clamp circuit coupled in parallel to the primary coil, the active clamp circuit comprising a second switch coupled in series with a first capacitor and a second capacitor; and
a controller coupled to the first switch and the second switch, the controller configured to:
turn the first switch on, so as to store energy in the primary coil;
turn the first switch off, so as to charge the first and the second capacitors in series;
turn the second switch on when a voltage across the first switch approaches a peak value, so as to discharge the first and the second capacitors in parallel; and
turn the second switch off when at least one of: a voltage across the first capacitor and a voltage across the second capacitor, falls to a predetermined voltage level.

### Claim 18 (depends on 17)

The power conversion apparatus of claim 17, wherein the first switch is turned on when a current is flowing through its body diode or when the voltage across the first switch is determined to reach a non-zero minimum voltage.

### Claim 19 (depends on 17)

The power conversion apparatus of claim 17, wherein the first capacitor and the second capacitor have the same capacitance.

### Claim 20 (depends on 17)

The power conversion apparatus of claim 17, wherein the active clamp circuit further comprises a first diode.

### Claim 21 (depends on 20)

The power conversion apparatus of claim 20, wherein the first diode is coupled in series with the first capacitor and the second capacitor to block any reverse current from discharging the first capacitor and the second capacitor in series.

### Claim 22 (depends on 20)

The power conversion apparatus of claim 20, wherein the active clamp circuit further comprises a second diode and a third diode.

### Claim 23 (depends on 22)

The power conversion apparatus of claim 22,
wherein the second diode is coupled in parallel with the first capacitor and the first diode,
wherein the third diode is coupled in parallel with the second capacitor and the first diode, and
wherein the second diode and the third diode are configured to allow a flow of reverse current to discharge the first capacitor and the second capacitor in parallel.

### Claim 24 (depends on 17)

The power conversion apparatus of claim 17,
wherein the voltage across the first switch, after the first switch is turned off and before the second switch is turned on, represents a sinusoidal voltage that includes a plurality of peak values, and
wherein the second switch is turned on when the voltage across the first switch approaches one of the plurality of peak values.