Parallel-mode extended-period quasiresonant convertor

A new circuit, a parallel-mode, extended-period, zero-current quasiresonant convertor (PM-EP-ZCQRC), is introduced. It has low switching losses, because the switching conditions are those of a quasiresonant convertor, but it operates at constant frequency by using the duty-ratio technique of conventional switched-mode power supplies for output regulation. The modes of operation of the circuit are described and analysed. The results of open-loop tests on a prototype circuit are presented and are shown to agree with predictions. The efficiency of the circuit was found to be 80 to 90% and a comparison of loss components with those in a quasiresonant convertor (QRC) is given.