Zero current switching forward power conversion apparatus and method with controllable energy transfer

摘要

An improved forward converter switching at zero-current incorporates a mechanism for selectively regulating the amount of forward energy which is delivered to a load during each converter operating cycle. Energy is transferred from a voltage source toward a load in discrete packets via a small effective inductance (specifically the small effective leakage inductance of a transformer) and a capacitor, the combination of which define a characteristic time scale for the rise and fall of current such that a switching device connected in series with the voltage source can be cycled on and off at zero-current. The capacitor is connected to the load via a second inductor. By incorporating a second bidirectional switch across the capacitor, and cycling the second switch on and off at appropriate times during a converter operating cycle, the amount of forward energy transferred toward the load may be regulated without incurring switching losses in the second bidirectional switching device, and control may also be asserted over reverse current flow from the load toward the second switch subsequent to forward energy transfer. The new topology allows a single converter to generate a multitude of voltage outputs, all of which may be maintained in regulation as the loads on the various outputs are varied, with no minimum load being required on any output.