AC/DC flyback converter with improved power factor and reduced switching loss

• US 5,991,172 A
• Filed: 03/02/1998
• Issued: 11/23/1999
• Est. Priority Date: 06/21/1996
• Status: Expired due to Term

• Current Assignee: Delta Electronics Incorporated
• Original Assignee: Delta Electronics Incorporated
• Inventors: Huber, Laszlo, Jovanovic, Milan M.
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US09/033,005
• Time in Patent Office: 631 Days
• Field of Search: 363/20, 363/21, 363/37, 363/81, 363/89, 363/97, 363/125, 363/132
• US Class Current: 363/21.14
• 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 3/33538 of the forward type H02M3/3353, H02M3/33569 take precedence
• 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 new single stage, single switch input current shaping circuit features substantially reduced turn-on switching losses of the switch in the flyback-converter. In this technique, the turn-on switching losses due to the discharge of the output capacitance of the switch are reduced by turning on the switch when its voltage is minimal or close to the minimal. To achieve the turn-on loss reduction for a wide range of line and load conditions, the flyback-converter stage is continuously operated at the boundary of the CCM and DCM by employing a variable-frequency control. In this technique the boost inductor can work either in the DCM or the CCM. The wide-bandwidth, variable-frequency control is implemented by detecting the onset of the DCM/CCM boundary and, subsequently, turning the switch on at the minimum switch voltage. The switch is turned off when the increasing primary current reaches a reference level set by the output-voltage feedback control circuit.

Claims

1. A single-stage single-switch flyback converter with input current shaping and output voltage regulation, comprising in combination:

rectified ac voltage means;

an energy-storage inductor having a first terminal and a second terminal, said first terminal connected to said rectified ac voltage means;

an energy-storage capacitor;

a switch which is periodically closed and opened;

an isolation transformer having a primary winding and a secondary winding, said primary winding connected in series with said switch across said energy-storage capacitor;

a first rectifier means having a first terminal and a second terminal, said first terminal connected to said second terminal of said energy-storage inductor and said second terminal connected to the primary winding of said isolation transformer;

an output-filter capacitor;

a load connected across the output-filter capacitor;

a second rectifier means connecting said secondary winding of said isolation transformer to said output-filter capacitor;

control means for periodically closing said switch to couple said primary winding to said energy storage capacitor, wherein said control means includes a first sensing means to detect the onset of the discontinuous-current mode operation of said isolation transformer and a delay means for closing said switch at a predetermined instant after said first sensing means detects the onset of the discontinuous current mode operation of said isolation transformer in order to turn-on said switch when the voltage across said switch is substantially at a minimum value;

said control means for periodically opening said switch to decouple said primary winding from said energy storage capacitor including a second sensing means to sense the current across said switch to turn off said switch when the current across said switch reaches a predetermined level.

2. A single-stage single-switch flyback converter with input current-shaping and output voltage regulation as in claim 1, wherein said first sensing means of said control means includes a zero-crossing detector for detecting the zero-crossing of the current in said secondary winding of said isolation transformer.

3. A single-stage single-switch flyback converter with input current shaping and output voltage regulation as in claim 1, wherein said first sensing means of said control means includes a voltage detector for detecting the instant when the voltage across said switch equals to the voltage across said energy-storage capacitor.

4. A single-stage single-switch flyback converter with input current shaping and output voltage regulation, comprising in combination:

rectified ac voltage means;

an energy-storage inductor having a first terminal and a second terminal, said first terminal connected to said rectified ac mains;

a first rectifier means having a first terminal and a second terminal, said first terminal connected to said second terminal of said energy-storage inductor;

an energy-storage capacitor;

a switch which is periodically closed and open;

an isolation transformer having a primary winding with a tap and a secondary winding, said primary winding connected in series with said switch across said energy-storage capacitor, and said tap of said primary winding connected to said second terminal of said first rectifier means;

an output-filter capacitor;

a load connected across output-filter capacitor;

a second rectifier means connecting said secondary winding of said isolation transformer to said output-filter capacitor;

control means for periodically closing said switch to couple said primary winding to said energy storage capacitor wherein said control means includes a first sensing means to detect the onset of the discontinuous-current mode operation of said isolation transformer and a delay means for closing said switch at a predetermined instant after said first sensing means detects the onset of the discontinuous current mode operation of said isolation transformer in order to turn-on said switch when the voltage across said switch is substantially at a minimum value;

said control means for periodically opening said switch to decouple said primary winding from said energy storage capacitor, includes a second sensing means to sense the current across said switch to turn off said switch when the current across said switch reaches a predetermined level.

5. A single-stage single-switch flyback converter with input current shaping and output voltage regulation, comprising in combination:

rectified ac voltage means;

an energy-storage inductor having a first terminal and a second terminal, said first terminal connected to said rectified ac voltage means;

a first rectifier means having a first terminal and a second terminal, said first terminal connected to said second terminal of said energy-storage inductor;

a second rectifier means having a first terminal and a second terminal, said first terminal connected to said second terminal of said energy-storage inductor;

an energy-storage capacitor;

a switch which is periodically closed and open;

an isolation transformer having a primary winding with a first tap and a second tap and a secondary winding, said primary winding connected in series with said switch across said energy-storage capacitor, said first tap of said primary winding connected to said second terminal of said first rectifier means and said second tap of said primary winding connected to said second terminal of said second rectifier means;

an output-filter capacitor;

a load connected across output-filter capacitor;

a third rectifier means connecting said secondary winding of said isolation transformer to said output filter capacitor;

control means for periodically closing said switch to couple said primary winding to said energy storage capacitor, wherein said control means includes a first sensing means to detect the onset of the discontinuous-current mode operation of said isolation transformer and a delay means for closing said switch at a predetermined instant after said first sensing means detects the onset of the discontinuous current mode operation of said isolation transformer in order to turn-on said switch when the voltage across said switch is substantially at a minimum value;

said control means for periodically opening said switch to decouple said primary winding from said energy storage capacitor also includes a second sensing means to sense the current across said switch to turn off said switch when the current across said switch reaches a determined level.

6. A single-stage single-switch flyback converter with input current shaping and output voltage regulation as in claim 5, wherein said first sensing means of said control means includes a zero-crossing detector for detecting the zero-crossing of the current in said secondary winding of said isolation transformer.

7. A single-stage single-switch flyback converter with input current shaping and output voltage regulation as in claim 5, wherein said first sensing means of said control means includes a voltage detector for detecting the instant when the voltage across said switch equals to the voltage across said energy-storage capacitor.

8. A single-stage single-switch flyback converter with input current shaping and output voltage regulation, comprising in combination:

rectified ac voltage means;

an energy-storage inductor having a first terminal and a second terminal, said first terminal connected to said rectified ac voltage means;

an energy-storage capacitor;

a switch which is periodically closed and open;

an isolation transformer having a primary and a secondary winding, said primary winding connected in series with said switch across said energy-storage capacitor;

means connecting said second terminal of said energy-storage inductor to said primary winding of said isolation transformer;

an output-filter capacitor;

a load connected across output-filter capacitor;

a synchronous rectifier connecting said secondary winding of said isolation transformer to said output filter capacitor;

control means for periodically closing said switch and said synchronous rectifier in mutually exclusive time intervals, wherein said control means includes a zero-current detector for detecting the zero-crossing of the current in said secondary winding of said isolation transformer and a first delay means and a second delay means, said first delay means used to define the instant at which said synchronous rectifier is opened after said zero-crossing detector detects the zero crossing of the current in said secondary winding of said isolation transformer, and said second delay means used to define the instant at which said switch is closed after said synchronous rectifier is opened in order to turn-on said switch when the voltage across said switch is zero or close to zero, and, wherein, said control means includes a sensing means to sense the current across said switch to turn off said switch and to turn-on said synchronous rectifier when the current across said switch reaches a predetermined level.

9. A single-stage single-switch flyback converter with input current shaping and output voltage regulation, comprising in combination:

rectified ac voltage means;

an energy-storage inductor having a first terminal and a second terminal, said first terminal connected to said rectified ac voltage means;

a rectifier means having a first terminal and a second terminal, said first terminal connected to said second terminal of said energy-storage inductor;

an energy-storage capacitor;

a switch which is periodically closed and open;

an isolation transformer having a primary winding with a tap and a secondary winding, said primary winding connected in series with said switch across said energy-storage capacitor, and said tap of said primary winding connected to said second terminal of said first rectifier means;

an output-filter capacitor;

a load connected across output-filter capacitor;

a synchronous rectifier connecting said secondary winding of said isolation transformer to said output filter capacitor;

control means for periodically closing said switch and said synchronous rectifier in mutually exclusive time intervals, wherein said control means includes a zero-current detector for detecting the zero-crossing of the current in said secondary winding of said isolation transformer and a first delay means and a second delay means, said first delay means used to define the instant at which said synchronous rectifier is opened after said zero-crossing detector detects the zero crossing of the current in said secondary winding of said isolation transformer, and said second delay means used to define the instant at which said switch is closed after said synchronous rectifier is opened in order to turn-on said switch when the voltage across said switch is zero or close to zero, and, wherein, said control means includes a sensing means to sense the current across said switch to turn off said switch and to turn-on said synchronous rectifier when the current across said switch reaches a predetermined level.

10. A single-stage single-switch flyback converter with input current shaping and output voltage regulation, comprising in combination:

rectified ac voltage means;

an energy-storage inductor having a first terminal and a second terminal, said first terminal connected to said rectified ac voltage means;

a first rectifier means having a first terminal and a second terminal, said first terminal connected to said second terminal of said energy-storage inductor;

a second rectifier means having a first terminal and a second terminal, said first terminal connected to said second terminal of said energy-storage inductor;

an energy-storage capacitor;

a switch which is periodically closed and open;

an isolation transformer having a primary winding with a first tap and a second tap and a secondary winding, said primary winding connected in series with said switch across said energy-storage capacitor, said first tap of said primary winding connected to said second terminal of said first rectifier means and said second tap of said primary winding connected to said second terminal of said second rectifier means;

an output-filter capacitor;

a load connected across output-filter capacitor;

a synchronous rectifier connecting said secondary winding of said isolation transformer to said output filter capacitor;

control means for periodically closing said switch and said synchronous rectifier in mutually exclusive time intervals, wherein said control means includes a zero-current detector for detecting the zero-crossing of the current in said secondary winding of said isolation transformer and a first delay means and a second delay means, said first delay means used to define the instant at which said synchronous rectifier is opened after said zero-crossing detector detects the zero crossing of the current in said secondary winding of said isolation transformer, and said second delay means used to define the instant at which said switch is closed after said synchronous rectifier is opened in order to turn-on said switch when the voltage across said switch is zero or close to zero, and, wherein, said control means includes a sensing means to sense the current across said switch to turn off said switch and to turn-on said synchronous rectifier when the current across said switch reaches a determined level.