Circuitry to maintain proper current transformer operation

Abstract

A circuit to maintain proper current transformer operation in a resonant transition converter circuit or any circuit having a wide range of reverse current present in a current transformer primary at the beginning of a power pulse. The circuit includes an active clamp which is applied to an extra secondary on the current transformer for the duration of a 'on' time of a switch associated with a particular current transformer. A diode of the active clamp is polarized to accept current in the secondary when primary current is reversed or negative flow. Thereby only small amounts of voltage, and thus volt-seconds will be developed on the transformer during reverse primary current, in turn keeping the current transformer out of reverse saturation. A current generator provides a bias current during the on time of the switch associated with the particular current transformer and switches a bias current into the main current transformer secondary during the power pulse to offset the negative primary current which occurs at the beginning of a power pulse.