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Abstract

A power conversion circuit, in which a flyback converter is modified with additional elements to provide both dissipationless snubbing and also input ripple cancellation. This is achieved by appropriate connection of an additional winding to the isolating transformer, without any need for a second transformer. The configuration of the secondary is conventional, and the switching transistor is connected in series with the primary winding across DC inputs (taken e.g. from a full-wave-rectified line voltage). The additional winding is connected on the primary side, and preferably has a near-unity turns ratio with the primary which is the inverse of the coupling coefficient. However, the additional winding is not connected between the two DC inputs, but instead has one end coupled through an intermediate capacitor to the corresponding end of the primary, and the other end coupled through a capacitor to the negative DC input. By use of appropriate reactances a balancing current is maintained in the additional winding, which keeps the total current through the primary absolutely flat. The intermediate capacitor which links the primary and additional windings also provides efficient snubbing: it catches the energy stored in the primary leakage inductance, and also limits the maximum voltage on the switch. This results in a converter with no ripple at the input, high efficiency, and very efficient snubbing. Moreover, by using a second active element for regeneration, energy loss during switching of the primary switch is minimized.

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