Transformerless DC-to-DC Converters with Large Conversion Ratios

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 ¿uk converter to incorporate a multistage capacitor divider. A particularly suitable application would be a 50V to 5V converter in which dc isolation is not required. The absense of a transformer and a larger duty ratio permits operation at very high switching frequency, and makes the circuit amenable to partial integration and hybrid construction techniques. An experimental three-stage voltage divider ¿uk converter converts 50V to 5V at 50W with an efficiency of 77% at 500 kHz and 71% at 1 MHz, higher than for a basic ¿uk converter operated at the same conditions.