Research On Active Clamp ZVS-PWM Forward Converter

Nowadays, the forward converter plays a more and more important role in low and middle power application. But, despite its merits, the traditional single-ended forward converter has some shortcomings, such as simple circuit, low parts count, low output ripple, etc, it also has some shortcomings. Firstly, the working mode of transistor is hard switch, which cause the difficulty to improve the switching frequency. Secondly, it needs a magnetic reset circuit and the magnetic core only works in No.1 quadrant. The development trend of the Switching Mode Power Supply (SMPS) is soft switching with high frequency, high power density and high efficiency. It is clear that the traditional single-ended forward converter is difficult to adapt to the trend, so, it is necessary to find a novel topology. The active clamp ZVS-PWM forward converter has been answered for with the merits of the soft switch technique and the magnetic reset technique. In this paper, the principle of the operation of the active clamp ZVS-PWM forward converter is analyzed, including the effect of the clamp voltage, the delay of the drive signal and the saturable inductor to the zero switching condition, etc. Then, according to the study of the soft-switching, synchronous rectifier and PCB planar transformer, achieved the design of the active clamp ZVS-PWM converter, and the design formulas of the key components were deduced, including clamp capacitance, PCB planar transformer, synchronous rectifier, output filter, etc. Lastly, Pspice simulation of the active clamp ZVS-PWM forward converter was achieved, and the simulation parameters were used to optimize the design. The experimental results have verified the validity of the theoretical analysis and the superiority of the converter.