A zero voltage switching asymmetrical half-bridge DC/DC converter with unbalanced secondary windings for improved bandwidth
This paper presents a modified PWM half-bridge DC/DC converter that can achieve zero voltage switching (ZVS) and can operate under current or voltage mode control. The proposed topology operates with complementary-control (asymmetrical duty cycle) and utilizes unbalanced transformer secondary windings and a low output inductance value to achieve an improved bandwidth and load transient response compared to the active clamp forward converter. Self-driven synchronous rectifiers are used to increase efficiency. The operation of the converter is discussed, along with a comparison to the balanced secondary topology and the active clamp forward converter. A method is presented to eliminate synchronous rectifier gate drive voltage stress caused by asymmetrically unbalanced gate drive waveforms. In addition, an averaged switch large signal model is presented for the converter. Simulation results are presented for a converter operating at 400 kHz, with a 48 VDC nominal input and a 5 VDC/5 A output.