# US 11,114,945 B2 · Secondary-controlled active clamp implementation for improved efficiency

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- Number: US 11,114,945 B2
- Document ID: US11114945B2
- Status: Granted
- Kind: B2
- Application number: 16/582,690
- Filed: 2019-09-25
- Published: 2021-02-25
- Granted: 2021-09-07
- Earliest claimed: 2019-08-22
- Assignees: Cypress Semiconductor Corporation
- Applicants: Cypress Semiconductor Corporation
- Inventors: Rashed Ahmed; Hariom Rai
- Web page: https://patentgrep.com/patent/US11114945B2

## CPC

- H02M 3/33592: {having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer}
- H02J 7/00: Circuit arrangements for charging or discharging batteries or for supplying loads from batteries
- H02M 3/33523: {with galvanic isolation between input and output of both the power stage and the feedback loop}
- H02M 1/342: {Active non-dissipative snubbers}
- 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)
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

Controlling an active clamp field effect transistor (FET) in a secondary-controlled active clamp converter is described. In one embodiment, an apparatus includes a primary-side FET coupled to a transformer, a secondary-side FET coupled to the transformer, and an active clamp FET disposed on a primary side of the transformer. A secondary-side controller is configured to control the active clamp FET across a galvanic isolation barrier.

## Claims

### Claim 1

A secondary-side controlled alternating current to direct current (AC-DC) converter comprising:
a primary-side field effect transistor (FET);
a secondary-side FET;
a transformer of the AC-DC converter, wherein the transformer is coupled to the primary-side FET and the secondary-side FET;
an active clamp FET coupled to the primary-side FET, wherein the active clamp FET is disposed on a primary side of the transformer; and
a secondary-side controller coupled to the transformer, wherein the secondary-side controller is configured to generate a first control signal and a second control signal, the first control signal to control the primary-side FET via a primary-side controller across a first pulse transformer coupled between the primary-side controller and the secondary-side controller, and the second control signal to control the active clamp FET across a galvanic isolation barrier provided by a second pulse transformer, wherein a gate of the active clamp FET is directly coupled to a primary winding of the second pulse transformer.

### Claim 2 (depends on 1)

The secondary-side controlled AC-DC converter of claim 1, wherein the secondary-side controller is to send the second control signal to the active clamp FET via the second pulse transformer.

### Claim 3 (depends on 2)

The secondary-side controlled AC-DC converter of claim 2, wherein the secondary-side controller comprises:
a first driver coupled to a gate of the secondary-side FET;
a second driver coupled to a primary side of the second pulse transformer; and
a circuit to generate the second control signal.

### Claim 4 (depends on 2)

The secondary-side controlled AC-DC flyback converter of claim 2, wherein the second pulse transformer is coupled to a synchronous rectifier gate driver, wherein the synchronous rectifier gate driver is to drive the active clamp FET via the second pulse transformer.

### Claim 5 (depends on 1)

The secondary-side controlled AC-DC flyback converter of claim 1, wherein the secondary-side controller is to control the secondary-side FET using a third control signal that is based on the second control signal.

### Claim 6 (depends on 1)

The secondary-side controlled AC-DC converter of claim 1, wherein the primary-side controller is coupled to the primary-side FET.

### Claim 7 (depends on 1)

The secondary-side controlled AC-DC converter of claim 1, wherein the active clamp FET is an n-type FET (NFET) comprising a floating ground.

### Claim 8 (depends on 1)

The secondary-side controlled AC-DC converter of claim 1, wherein the active clamp FET is a p-type FET (PFET) comprising a referenced ground.

### Claim 9 (depends on 1)

The secondary-side controlled AC-DC converter of claim 1, further comprising a capacitor coupled between the active clamp FET and a rectified DC line (VIN).

### Claim 10 (depends on 1)

The secondary-side controlled AC-DC converter of claim 1, wherein a source of the secondary-side FET is coupled to a GND terminal of a USB-C connector.

### Claim 11

A method comprising:
generating, by a secondary-side controller in a secondary-side controlled alternating current to direct current (AC-DC) flyback converter, a first control signal, a second control signal, and a third control signal;
controlling, by the secondary-side controller, a secondary-side field effect transistor (FET) coupled to a flyback transformer, using the third control signal, wherein the third control signal is based on the second control signal;
controlling, by the secondary-side controller, a primary-side FET using the first control signal via a primary-side controller across a first pulse transformer coupled between the primary-side controller and the secondary-side controller; and
controlling, by the secondary-side controller, an active clamp FET that is disposed on a primary side of the flyback transformer using the second control signal, wherein the second control signal is sent across a galvanic isolation barrier provided by a second pulse transformer, wherein a gate of the active clamp FET is directly coupled to a primary winding of the second pulse transformer.

### Claim 12 (depends on 11)

The method of claim 11, further comprising:
determining, by the secondary-side controller, output power on a direct current (DC) output line;
activating the secondary-side FET and the active clamp FET for a first duration of time in response to determining that the output power is above a threshold; and
de-activating the secondary-side FET and the active clamp FET for a second duration of time in response to determining that the output power is below the threshold.

### Claim 13

An alternating current to direct current (AC-DC) power adapter device comprising:
a USB-C connector;
a power converter comprising a transformer and a rectifier coupled between AC terminals and DC terminals, the rectifier to convert AC power on the AC terminals to DC power on the DC terminals, and the transformer to provide galvanic isolation between the AC terminals and the DC terminals;
a primary-side field effect transistor (FET);
a secondary-side FET;
an active clamp FET coupled to the secondary-side controller, wherein the active clamp FET is disposed on a primary side of the transformer; and
a secondary-side controller coupled to the transformer, wherein the secondary-side controller is configured to generate a first control signal and a second control signal, the first control signal to control the primary-side FET via a primary-side controller across a first pulse transformer coupled between the primary-side controller and the secondary-side controller, and the second control signal to control the active clamp FET across a galvanic isolation barrier provided by a second pulse transformer, wherein a gate of the active clamp FET is directly coupled to a primary winding of the second pulse transformer.

### Claim 14 (depends on 13)

The AC-DC power adapter device of claim 13, wherein the secondary-side controller is to control the secondary-side FET using a third control signal that is based on the second control signal.

### Claim 15 (depends on 13)

The AC-DC power adapter device of claim 13, wherein the secondary-side controller comprises:
a first driver coupled to a gate of the secondary-side FET;
a second driver coupled to a primary side of the pulse transformer; and
a circuit to generate the second control signal.

### Claim 16 (depends on 13)

The AC-DC power adapter device of claim 13, wherein the second pulse transformer is coupled to a synchronous rectifier gate driver, wherein the synchronous rectifier gate driver is to drive the active clamp FET via the second pulse transformer.

### Claim 17 (depends on 13)

The AC-DC power adapter device of claim 13,
wherein the primary-side controller is coupled to the primary-side FET.