High-frequency off-line power conversion using quasi-resonant and multi-resonant techniques

Three recently-proposed power conversion technologies, the zero-current-switching (ZCS) and zero-voltage-switching (ZVS) quasi-resonant techniques, and the zero-voltage-switching multi-resonant technique, are evaluated for high-frequency, off-line applications. The study is performed with emphasis on the conversion-frequency range, efficiency, load range, input-voltage range, output power, dynamic response, and power density.

A comprehensive dc analysis of the half-wave and full-wave, half-bridge zero-current-switched quasi-resonant converters (QRCs) is presented. Design procedures for closed-loop design of the converters are also derived. The procedures are used to design and fabricate half-wave and full-wave converters operating in the low-megahertz range and experimentally assess their suitability for high-frequency, off-line power conversion.

The zero-voltage-switching technique is employed to further increase the conversion frequency. First, the half-bridge zero-voltage-switched quasi-resonant converter is analyzed and the trade-offs between its frequency range, load range, and efficiency are examined in detail. The multi-resonant-switch concept is applied to this converter to improve its characteristics, primarily its load range.

A complete dc analysis of the zero-voltage-switched multi-resonant converter (MRC) is given and the dc voltage-conversion-ratio characteristics are derived. A graphic design procedure for the converter is established and is used to build an experimental 100 W, off-line converter operating in the frequency range of 2 MHz to 8 MHz.

Finally, a comprehensive comparison of the QRCs and MRCs is performed and conditions where their applications appears most desirable are defined.