Resonant-mode power supplies: a primer

The operation of the resonant-mode power supply is explained. The focus of this article is the quasi-resonant supply, so named because a power switch turns it off at intervals, interrupting the resonant cycle. The supplies have only become commercially feasible in the last two years, in part because particular kinds of transformers, capacitors, and controllers have just become available. The topologies possible in resonant mode are discussed; zero-current-switching and zero-voltage-switching topologies are considered in some detail. Points that should be kept in mind in designing components for resonant-mode power supplies are also addressed.<>