Design, performance, and application of a new bipolar synchronous rectifier

A bipolar transistor which is specifically designed for synchronous rectifier applications is described with emphasis placed on its design and performance. It is shown that as opposed to conventional devices such as the Schottky, the proposed transistor has an emitter-base voltage exceeding 50 V, which in effect allows for first and third quadrant blocking. Moreover, this feature enables the transistor to be used in a pulse width modulation mode where both regulation and rectification can be achieved in the power supply secondary. A novel base drive circuit is employed which results in only a minor increase in complexity, but allows for operation at switching frequencies up to 250 kHz.