Research And Design Of Active Clamp Forward Converter With Soft Switching

Modern electronic products are becoming more and more smaller and demand highefficiency, it makes the power supply should be of high power density, efficiency, light, smallsize and green, the techniques of soft-switching and synchronous rectification are playing animportant role in this development of the power supply.The topology of active clamp forward converter with synchronous rectification can reachto soft switching due to its active clamp circuit, and the power transformer can be reset, theduty of the topology can be over50%. Moreover, it can not only mend spike current andvoltage but also offers the main and auxiliary switches to achieve zero-voltage-switching(ZVS). The synchronous rectification replaces the diode is used to reduce conduction losses.Thus, the efficiency of the converter can be improved.At first, the paper presents several ways of power transformer reset and the analysis ofsynchronous rectification. The choice of high or low side to apply the active clamp techniqueresults in subtle differences in circuit implementation. The operation of the circuit can bedivided into12linear stages over one switching period shown in the paper as well as the keyfactor to achieve ZVS. And then presents the calculation of some important parametersincluding the clamp capacitor and power transformer. The negative drive to the auxiliaryswitch and voltage self-driven to the synchronous rectifiers are designed based on thetopology. The feedback control circuit composed of peak current mode controller UCC2891,PC817and TL431. Finally, the simulation was built in the Pspice according to the results ofthe various designed parameters to analyze and optimize the design.A prototype with45~72V input and12V/3A output and the switching frequency ofwhich is100kHz has been implemented to verify the theoretical and simulation analysis. Afterexperimental verification, the main and auxiliary switches and the synchronous rectifiers allcan achieve zero voltage turn-on and turn-off, the full load efficiency is85.6%and otherperformances of the converter meet the design requirements as well.