Method and apparatus for reduction of energy loss due to body diode conduction in synchronous rectifiers

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United States Patent and Trademark Office

A method and apparatus for preventing current flow through the integral body diode of an electronic switch (e.g. MOSFET) in the secondary circuit of a synchronous rectifier. In a conventional synchronous rectifier, body diode current 31a 31b occurs during dead times 32a 32b. In the present invention, current steering pulses 40 are applied to the secondary circuit to oppose freewheeling current flow through the integral body diode. The current steering pulses produce a current that maintains the body diode in a reverse-biased state. Also, body diode current 31a 31b is prevented in the invention by short-circuiting a primary winding 19 of a transformer. The present invention prevents body diode conduction energy losses, as well as reverse recovery losses. The present invention is applicable to many different kinds of synchronous rectifiers such as current doubling rectifiers, center-tapped rectifiers, full bridge rectifiers.