Synchronous rectification in a flyback converter

• US 6,373,727 B1
• Filed: 03/09/2001
• Issued: 04/16/2002
• Est. Priority Date: 03/10/2000
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Hedenskog, Bo, Svensson, Andréas
• Primary Examiner(s): Han, Jessica
• Application Number:
  US09/801,879
• Time in Patent Office: 403 Days
• Field of Search: 363/16, 363/20, 363/21.06, 363/21.12, 363/21.14, 363/21.15, 363/21.18, 363/97
• US Class Current: 363/21.14
• 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 flyback converter has a primary side including a main switch and a control device and a delay circuit. The converter has a secondary side including a drive circuit controlling a rectifying switch. The drive circuit has a first part including a first transistor, a first discharge diode and an on-node and a second part including a second transistor, a second discharge diode and an off-node. The control device is connected to the drive circuit via at least one drive capacitor to the on- and off-nodes. The control device issues drive pulses to the main switch through the delay circuit and to the drive circuit. The drive circuit has a first mode of operation in a flyback phase, which is triggered when the main switch is turned off and the rectifying switch is rendered conducting. A second mode of operation is a forward phase, which is triggered when the main switch is turned on and the rectifying switch is rendered non-conducting. The flyback converter includes few components and the main switch is efficiently prevented from conducting simultaneously with the rectifying switch.

Claims

1. A flyback converter comprising:

a primary side including a main switch, a control device, and a delay circuit, and

a secondary side including a drive circuit and a rectifying switch, the drive circuit including;

a turn-on part arranged to be activated when the main switch is turned-off to make the rectifying switch conducting, and

a turn-off part arranged to be activated when the main switch is turned-on to make the rectifying switch non-conducting, the turn-on part including;

a first transistor and a first discharge diode coupled between a base and an emitter of the first transistor,

wherein the control device is coupled to the base of the first transistor via a drive capacitor.

2. The flyback converter of claim 1, wherein the first transistor is a PNP-transistor.

3. The flyback converter of claim 1, wherein the turn-off part includes a second transistor, a second discharge diode coupled between a base and an emitter of the second transistor, and the drive capacitor coupled to the base of the second transistor.

4. The flyback converter of claim 1, wherein the second transistor is an NPN-transistor.

5. The flyback converter of claim 1, wherein the main switch includes a MOSFET.

6. The flyback converter of claim 1, wherein the rectifying switch is a charge controlled component.

7. The flyback converter of claim 1, wherein the rectifying element comprises an MOSFET or an IGBT.

8. The flyback converter of claim 1, wherein the delay circuit is coupled between the main switch and the control device, and the drive capacitor is coupled to the control device.

9. A flyback converter comprising:

a primary side including a main switch, a control device, and a delay circuit, and a secondary side including a drive circuit and a rectifying switch,

wherein the control device is coupled by a main switch control line to the main switch, the main switch control line includes the delay circuit, and the control device is configured to issue control pulses transmitted on the main switch control line through the delay circuit to the main switch and on a drive circuit control line transmitted to the drive circuit,

wherein the drive circuit includes a turn-on part arranged to be activated when the main switch is turned-off to make the rectifying switch conducting and a turn-off part arranged to be activated when the main switch is turned-on to make the rectifying switch non-conducting,

and wherein the drive circuit control line includes at least one drive capacitor coupled at one end to a control terminal of one of the turn-on and turn-off parts.