A Novel Hybrid 4:1 Step Down Converter Using an Autotransformer with DC Winding Current

Abstract

This work presents a non-isolated hybrid topology targeting at 4:1 fixed ratio and high output current applications. This topology can be regarded as a compact integration of switched capacitor and autotransformer. The switched capacitors are soft charged and the two winding currents in the autotransformer are auto balanced. The transformer has quasi-DC current with negligible AC winding losses. To further study the performance of the transformer in the proposed circuit, the transformer is simulated with different current waveforms, and the results show that with quasi-DC current the winding losses do not increase with switching frequency, and they are at least two times lower than the losses generated from sinusoidal or square current. The proposed circuit is measured at 24V-6V step-down and up to 25A output current, achieving 96.7% peak efficiency. The same transformer is also tested in a full bridge testbench to compare winding losses with square current by measuring its temperature.