Analysis of a series-resonant converter with ZVS-PWM control

Many resonant converters have been proposed previously, and their soft-swit ching techniques have yielded prominent features of high efficiency and low noise. However, the variable-frequency control is normally used to control the output voltage, and it results in a few problems such as the lowest sw itching frequency limiting the size reduction of the output filter and nois e filter, and the beat phenomenon. In order to eliminate these limitations, we had previously proposed a novel ZVS-PWM controlled current-mode resonan t converter with an active-clamp circuit. The purpose of this paper is to c larify the steady-state characteristics of this converter. First, the stead y-state characteristics are analyzed, and then an analytical expression for the output voltage is derived through the concept of an equivalent ac resi stance. Second, the zero-voltage-switching (ZVS) region is clarified. Final ly, these analytical results are confirmed by experiment. Thus, it is possi ble to realize both ZVS operation and PWM control at a constant switching f requency. (C) 1999 Scripta Technica, Electron Comm Jpn Pt 2, 83(1): 59-65, 2000.