Active clamp used to maintain proper current transformer operation

Abstract

An active clamp used 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 active clamp is connected directly to a secondary of the current transformer and is placed in an active state for the duration of the 'on' time of a switch associated with a particular current transformer. A diode, FET combination of the active clamp provides a path for current to flow 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 resistive-capacitive network allows the active clamp to use the circuit drive signal to place the active clamp in an on state.