A unified model for the ZVS DC-DC converters with active clamp

Active clamp DC-DC converters are recently introduced family of two switch pulse width modulated converters featuring zero-voltage switching. The topological structure of these converters in relation to their hard-switched PWM converters is highlighted. With proper designation of the circuit variables (throw voltage V and the pole current I), all these converters are seen to be governed by an identical set of equations. In this framework, these circuits exhibit 6 sub-periods per cycle with identical current waveform in the resonant inductor. With idealized switches, the steady-state performance is obtainable in an analytical form. This set of equations may be solved through a simple spreadsheet programme. The steady-state performance provides a design constraint on the normalized current. The conversion ratio of the converter is also readily available. A generalized equivalent circuit emerges for all these converters from this steady-state conversion ratio. It is interesting to note that this equivalent circuit provides a dynamic model as well. The circuit model proposed in this paper enables one to use the familiar state space averaged results of the standard PWM DC-to-DC converters (both steady-state and dynamic) for their ZVS active clamp counterparts.