Transformerless DC-to-DC converters with large conversion ratios

Abstract

A new switching dc-to-dc converter is introduced in which large voltage step-down ratios can be achieved without a very small duty ratio and without a transformer. The circuit is an extension of the Ćuk converter to incorporate a multistage capacitor divider. A particularly suitable application would he a 50-V to 5-V converter in which dc isolation is not required. The absence of a transformer and a larger duty ratio permits operation at a high switching frequency and makes the circuit amenable to partial integration and hybrid construction techniques. An experimental 50-W three-stage voltage divider Ćuk converter converts 50 V to 5 V at 500 kHz, with efficiency higher than for a basic Ćuk converter operated at the same conditions. A corresponding voltage-multiplier Ćuk converter is described, and also dual buck-boost-derived step-down and step-up converters.