Resonant Transition Topologies For Push-Pull And Half-Bridge DC-DC Converters

Abstract

Switched mode power supplies (SMPS) are being extensively used in most power conversion processes. The analysis, design and modeling processes of hard-switched converters are mature, where the switching frequency was limited to a few 10's of kHz. The present direction of evolution m SMPS is towards higher efficiency and higher power density. These twin objectives demand high switching frequency and low overall losses. Soft switching results in practically zero switching losses and extends the switching frequency to 100's of kHz and beyond.

This thesis presents novel variants of push-pull and half-bridge DC-DC converters with soft switching properties. The proposed topology uses two additional switches and two diodes. The additional switches introduce freewheeling intervals m the circuit and enable loss-less switching. Switch stress, control and small signal model are similar to hard-switched PWM converter. Synchronous rectifiers are used in the ZVS push-pull converter to achieve high efficiency. It is interesting to see that the drives for the synchronous rectifier device are practically the same as the additional switches.

The contributions made in this thesis are 1) Idealized analysis and design methodology for the proposed converters. 2) Validation of the design through circuit simulation as well as prototypes - a 300kHz, 200W push-pull converter and a 300kHz, 640W half-bridge converter. 3) Closed loop control design for desired bandwidth and accuracy Verification of loop gain through network analyzer instrumental for the same The loop gain bandwidth achieved is about 30kHz for the push-pull converter and 20kHz for half-bridge converter.

An appendix has been devoted to explain the use of network analyzer. Characterization of coil, transformer and capacitor are explained in detail. Measurement techniques for measuring the small signal parameters of power supply are also explained in the appendix.