Forward Converter with Active Clamp and Synchronous Rectifier

Abstract

The paper deals with analysis of the AC/DC converter, designed for industrial use where a small output voltage (several volts) and high output current (several tens of amperes) is requested. The output power of converter is 240 W, whereby its main particularity is galvanic isolation, active clamp on the primary side and synchronous rectification on the secondary side. Main electrical parameters are UINMIN = 85 VAC, UINMAX = 265 VAC, UOUT = 24 VDC, IOUT = 10A,  fSW = 140 kHz. The compensation of power factor is realized with the use of PFC and thus the minimization of inductive character of the device in the wide range of input voltage is secured. As most effective solution Forward converter has been selected, whereby for reduction of switching losses at the primary side, the active clamp with soft-switching function (zero voltage switching) is being used. On the other side, for secondary side loss reduction, synchronous rectifier is utilized. Due to these solutions, we achieved maximum efficiency of η = 87,4 % and the value of PF was 0,98, so the converter acts as pure resistive load. In this way, the apparent power is reduced, thus no other compensation is necessary.  This value can still be improved by several percent with the use of debugged RC filters and with transistors with better field of merit properties. The outcome of proposed solution is reduction of negative environmental influences and increase of qualitative indexes of power supply. Almost these two factors are required for future generation of power converters.
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