Switching converter with open-loop input voltage regulation on primary

Abstract

An isolated switching dc-to-dc converter is provided with a novel open-loop input voltage regulation on the primary side and the full regulation and independent protection of each of multiple outputs on the secondary side using an auxiliary circuit comprising a current bidirectional switch Q.sub.a and a capacitor C.sub.a on the primary side in a series circuit connected in parallel with a main current bidirectional switch Q to assure a continuous conduction mode for operation of the primary boost-like converter, and consequently preserves the simplicity of open-loop input voltage regulation for all loads from no load to full load. The auxiliary switch Q.sub.a is very efficient with only a fraction (5% or less) of the losses of the main active switch Q. The ideal dynamic response approaching theoretical limits is achieved for both line and load transients together with a high efficiency (85%) and record power density (20 W per cubic inch) for multiple output converters. Finally, the whole power supply needs isolation only at the main power transformer, since the need for isolation in the open-loop input and closed-loop output regulation control and drive circuitry is completely eliminated.