Self-driven synchronous rectification scheme for wide output range

A self-driven synchronous rectifier circuit, comprising:

• an input terminal for receiving a voltage;
• a first power switch electrically connected to the input terminal;
• a second power switch electrically connected to the input terminal;
• a transformer connected to the first power switch and the second power switch, the transformer including a primary winding, a secondary winding and an auxiliary winding;
• a first synchronous rectifier connected to the first power switch via the transformer;
• a second synchronous rectifier connected to the second power switch via the transformer;
• a first diode connected to the second synchronous rectifier;
• and
• a second diode connected to the first synchronous rectifier, wherein the first and second diodes are operable to prevent the first and second synchronous rectifiers from conducting at the same time;
• a third diode connected to the second synchronous rectifier;
• and
• a fourth diode connected to the first synchronous rectifier, the third diode operating to restrain gate overvoltage of the first synchronous rectifier, the fourth diode operating to restrain gate overvoltage of the second synchronous rectifier.

A method of self-driving a synchronous rectifier circuit, the method comprising:

• A. during a first part of a cycle:
• (1) turning a first synchronous rectifier on;
• (2) turning a second synchronous rectifier off such that the first and second synchronous rectifiers do not conduct at the same time,
• B. during a second part of the cycle:
• (3) turning on the second synchronous rectifier;
• (4) turning off the first synchronous rectifier such that the first and second synchronous rectifiers do not conduct at the same time;
• (5) reversing a voltage across a transformer in response to the turning on and turning off of the first and second synchronous rectifiers;
• and
• restraining gate overvoltage of the first and second synchronous rectifiers.

A method of self-driving a synchronous rectifier circuit having a transformer with a primary winding, a secondary winding, and an independently coupled auxiliary winding, the method comprising:

• during a first part of a cycle:
• (1) turning a first synchronous rectifier on by applying a gate voltage thereto via the auxiliary winding;
• (2) turning a second synchronous rectifier off such that the first and second synchronous rectifiers do not conduct at the same time,
• during a second part of the cycle:
• (3) turning on the second synchronous rectifier by applying a gate voltage thereto via the auxiliary winding;
• (4) turning off the first synchronous rectifier such that the first and second synchronous rectifiers do not conduct at the same time;
• and
• (5) reversing a voltage across the secondary of the transformer transformer in response to reversal of the voltage across the primary of the transform to effect the turning on and turning off of the first and second synchronous rectifiers.