Two novel clamped-mode resonant converters are analyzed. These clamped-mode converters operate at a constant frequency while retaining many desired features of conventional resonant converters such as fast responses, zero-voltage turn-on or zero-current turn-off, and low EMI levels, etc. The converters are able to regulate the output from no load to full load and are particularly suitable for off-line, high-power applications.

To provide insights to the operations and derive design guidelines for the clamped-mode resonant converters, a complete dc characterization of both the clamped-mode series-resonant converter and the clamped-mode parallel-resonant converter, operating above and below resonant frequency, is performed. State-plane analysis techniques are employed. By portraying the converters' operation on a state-plane diagram, various circuit operating modes are identified. The boundaries between different operating modes are determined. The regions for natural and force commutation of the active switches are defined. Important dc characteristics, such as control-to-output transfer ratio, rms inductor current, peak capacitor voltage, rms switch currents, average diode currents, switch turn-on currents, and switch turn-off currents are derived to facilitate the converter designs.

To illustrate the converter designs in different operating regions, several design examples are given. Finally, three prototype circuits are built to verify the analytical results.