Analysis and optimized design of ZVZCS half bridge flyback converter with reduced voltage oscillation across diode

Abstract

Commercially, the widely used converter is flyback converter. Because it has no output inductance, so its cost is much lower than other converters. In addition, it has no reset circuit for magnetizing inductance; as a result, the power system has a less mass, and light weight. But it has several problems, and one of the most serious problems is hard switching operation of main switch. Hard switching causes high voltage surge across switch and diode, which renders too much stress on switch and diode, especially in high voltage applications. To remove the hard switching problem, conventional half bridge flyback converter (HBFC) 1 was proposed. In conventional HBFC 1, the main switch is zero voltage switched (ZVS) by leakage inductance. Moreover, in flyback converter, the voltage of main switch is the sum of the input source voltage $(V_s)$ and reflected output voltage $(V_o/n)$, but in conventional HBFC 1, the voltage stress of switches are clamped to input voltage. So, in voltage stress aspect, the conventional HBFC 1 is much better than flyback converter. However, conventional HBFC 1 also has some problems: one is narrow ZVS range of main switch; and the other is reverse recovery problem of rectifier diode, which causes tremendous voltage oscillation across diode. To widen the ZVS range of main switch and solve the diode reverse recovery problem, conventional HBFC 2 was proposed. In conventional HBFC 2, ZVS of main switch is realized by magnetizing current, and the ZVS range of main switch is much wider than conventional 1. To eliminate the reverse recovery problem, diode ZCS is realized by the resonance of leakage inductance and blocking capacitance. Finally, voltage oscillation caused by diode reverse recovery problem is reduced to some extent. However, even if switch ZVS and diode ZCS are assured, voltage oscillation across rectifier diode still exists. In conventional HBFC, the diode is equally modeled as the ideal diode. When diode is blocked, the...