Two methods to drive synchronous rectifiers during dead time in forward topologies

Conventional self-driven synchronous rectification forward topology cannot provide drive voltage for freewheeling synchronous rectifier (SR) when transformer magnetic reset process is over and zero voltage appears across the transformer windings. This causes SR body diode turn on and deteriorates the performance of synchronous rectification. In this paper, two SR drive mechanisms, gate charge retention drive and energy recovery current drive are presented. Both mechanisms can solve this body diode turn on problem. The current driven method also provides constant drive voltage and allows parallel operation. Two 250 kHz, 48 V input 5 V/10 A output DC-DC modules are designed using these two methods. 92% efficiency is achieved at full load for both modules.