Lossless active clamp for secondary circuits

Abstract

Lossless snubbers have been developed with the emphasis on snubbing the primary side switches. With the switching losses in the primary being minimised, the secondary diode losses become a major limiting factor of converter operating frequency and total efficiency. To address this problem, a new active lossless clamp for secondary diodes of switch mode converters is proposed. The clamp recycles diode reverse recovery energy stored in the transformer leakage inductance and allows diodes with smaller reverse voltage to be used in the output circuit. A double reduction of power loss is obtained by recovering the leakage inductance energy and through lower conduction loss of the output diodes. The clamp operates over the full range of load from open circuit to short circuit and is fully compatible with resonant transition type circuits. This paper analyses the operation of the proposed regenerative clamp and discusses the application to various secondary circuits. Finally, the clamp operation is verified by experimental results obtained from the application of the regenerative clamp on a compact 3 kW rectifier.