《总结正激变换器各种复位方式辅助绕组》.ppt

adlsong Dual Switches ConvertersSelf Reverse Voltage Clamp Magnetism Current Reset The Forward Converter A Review of Transformers: Voltage applied across primary is transformed into a voltage across the secondary, with polarity following the dotted terminals, in accordance with the relation: Vp/Vs = Np/Ns Current going into the dotted primary terminal is transformed and goes out of the secondary terminal, following the relation: Ip/Is = Ns/Np An ideal transformer does not store energy, hence: Pin = Pout or Pp = Ps. 开关管关断时激磁能量由复位绕组传输到输入电容,无功率损耗. 简单,复位电路只要一个二极管和一个复位绕组 最大占空比小于50% 保证变压器复位,因而最大输入电压时占空比小,输入电压范围窄. 最大占空比50%,开关管额定电压VDS= 2VIN 由于复位绕组使漏感大 输出短路时复位二极管大有电流和电压应力 Elements of primary zener clamp circuit Non dissipative type snubber with passive components L, C and D, but higher cost than RCD type clamp circuit Operating duty limits as same as RCD voltage clamp Energy recycle and clamp VDS at passive linear mode thru C to Bulk Bus during main switch turn off and LC resonant transition mode to move the energy storage of C to L during main switch turning on Critical point: Very high peak current on the leading edge of switching current of Q1 at switch turn on because the energy storage of “C” transfer to “L” thru Q1 Higher power efficiency than RCD type but lower than “Conventional” because addition one more diode dissipation To avoid DC bias on “L”, should be selected low leakage current of the Diode that in series on current loop M1: t0~t1S1/Dr is on and Sa/Dc is off Add Auxiliary Switch Sa Basic RCD Clamp Remove Resistor Compared with RCD, Cc can discharge to inversely deeply magnetize the magnetization inductance via Sc. Active Clamp Reset Forward Converter Sa: auxiliary switchS1: main switchDa: intrinsic parasitic diode inside SaD1: intrinsic parasitic diode inside S1C1: intrinsic parasitic capacitor inside Sa and external capacitor Active Clamp Reset Forward Converter 1. Usually need high side drive for high side activ