Forward-flyback topology switched mode power supply

Patent metadata

Field	Value
Publication number	US-9559601-B2
Application number	US-201314235931-A
Country	US
Kind code	B2
Filing date	Feb 28, 2013
Priority date	Feb 28, 2013
Publication date	Jan 31, 2017
Grant date	Jan 31, 2017

Abstract

A switched mode power supply ( 400 ), comprising a transformer ( 410 ) having a primary winding ( 410 - 1 ), a transformer core ( 410 - 3 ) configured to store energy transferred thereto from the primary winding ( 410 - 1 ) during operation, and a secondary winding ( 410 - 2 ) having a first terminal (T 1 ) and a second terminal (T 2 ). The switched mode power supply also has a primary side circuit (Q 1 , Q 2 , C 1 ) arranged to generate voltage pulses and thereby to drive the primary winding ( 410 - 1 ) of the transformer ( 410 ), and a secondary side circuit comprising a rectification circuit connected to the secondary winding ( 410 - 2 ) at the first and second terminals (T 1 , T 2 ). The rectification circuit is arranged such that during a forward phase of operation of the switched mode power supply, in which the primary winding ( 410 - 1 ) is driven by the primary side circuit to magnetize, and store energy in, the transformer core ( 410 - 3 ), a current induced to flow in the secondary winding ( 410 - 2 ) from the second terminal (T 2 ) to the first terminal (T 1 ) is output by the rectification circuit. The rectification circuit is further arranged such that during a fly-back phase of operation of the switched mode power supply, in which the magnetization of the transformer core ( 410 - 3 ) is reset, a current induced to flow in the secondary winding from the first terminal (T 1 ) to the second terminal (T 2 ) of the secondary winding ( 410 - 2 ) is output by the rectification circuit so that energy stored in the transformer ( 410 ) during the forward phase of operation is output by the rectification circuit.

First claim

The invention claimed is:

1. A switched mode power supply, comprising:
a transformer comprising a primary winding, a transformer core configured to store energy transferred thereto from the primary winding during operation, and a single, non-tapped secondary winding having a first terminal and a second terminal;
a primary side circuit arranged to generate voltage pulses and thereby to drive the primary winding of the transformer; and
a secondary side circuit comprising a rectification circuit connected to the secondary winding at the first and second terminals, wherein the rectification circuit is semi-synchronous, comprises one or more transistors and one or more diodes, and is arranged such that:
during a forward phase of operation of the switched mode power supply, in which the primary winding is driven by the primary side circuit to magnetize, and store energy in, the transformer core, a current induced to flow in the secondary winding from the second terminal to the first terminal is output by the rectification circuit; and
during a fly-back phase of operation of the switched mode power supply, in which the magnetization of the transformer core is reset, a current induced to flow in the secondary winding from the first terminal to the second terminal of the secondary winding is output by the rectification circuit so that energy stored in the transformer during the forward phase of operation is output by the rectification circuit; and

wherein the secondary side circuit further comprises a voltage limiter circuit configured to provide signals from the secondary winding to one or more gate terminals of the one or more transistors.

2. A switched mode power supply according to claim 1 , wherein the rectification circuit comprises:
a first rectifier and a second rectifier connected to the first and second terminals of the secondary winding, respectively, the first and second rectifiers being further connected to a first output terminal of the switched mode power supply; and
a third rectifier and a fourth rectifier connected to the first and second terminals of the secondary winding, respectively, the third and fourth rectifiers being further connected to a second output terminal of the switched mode power supply,
wherein the polarities of said rectifiers are arranged such that, during the forward phase of operation of the switched mode power supply, the current induced to flow in the secondary winding from the second terminal to the first terminal is output by the rectification circuit and, during the fly-back phase of operation of the switched mode power supply, the current induced to flow in the secondary winding from the first terminal to the second terminal of the secondary winding is output by the rectification circuit.

3. A switched mode power supply according to claim 2 , wherein the secondary side circuit further comprises an inductor connected to the rectification circuit and an output terminal of the switched mode power supply.

4. A switched mode power supply according to claim 3 , wherein a first end of the inductor is connected to both the third and fourth rectifiers, and a second end of the inductor is connected to the second output terminal of the switched mode power supply.

5. A switched mode power supply according to claim 3 , wherein a first end of the inductor is connected to the third rectifier, and a second end of the inductor is connected to both the fourth rectifier and the second output terminal of the switched mode power supply.

6. A switched mode power supply according to claim 2 , wherein:
each of the first and second rectifier is a synchronous rectifier;
each of the third and fourth rectifier is a diode;
the switched mode power supply comprises a control signal generator arranged to generate control signals to control switching of the first and second synchronous rectifiers; and
the polarities of the diodes in the rectification circuit and the control signals which the control signal generator is arranged to generate are such that, during the forward phase of operation of the switched mode power supply, the current induced to flow in the secondary winding from the second terminal to the first terminal is output by the rectification circuit and, during the fly-back phase of operation of the switched mode power supply, the current induced to flow in the secondary winding from the first terminal to the second terminal of the secondary winding is output by the rectification circuit.

7. A switched mode power supply according to claim 6 , wherein the control signal generator comprises at least a portion of the secondary winding.

8. A switched mode power supply according to claim 2 , wherein:
each of the rectifiers is a synchronous rectifier; and
the switched mode power supply further comprises a control signal generator arranged to generate control signal to control switching of the synchronous rectifiers such that, during the forward phase of operation of the switched mode power supply, the current induced to flow in the secondary winding from the second terminal to the first terminal is output by the rectification circuit and, during the fly-back phase of operation of the switched mode power supply, the current induced to flow in the secondary winding from the first terminal to the second terminal of the secondary winding is output by the rectification circuit.

Assignees

• Ericsson Telefon Ab L M
• ERICSSON TELEFON AB L M (publ)

Inventors

• Persson Oscar
• Appelberg Mikael
• Karlsson Magnus

Classifications

• H02M3/33538 Primary

  of the forward type (H02M3/3353, H02M3/33569 take precedence) · CPC title

• H02M3/33592

  having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer · CPC title

• H02M3/33546 Primary

  with automatic control of the output voltage or current (H02M3/33561 takes precedence) · CPC title

• Y02B70/1475

  Cross-Sectional Technologies · mapped topic

• H02M1/08

  Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters · CPC title