True soft switching by timed steering of a current source
Abstract:
A method for operation of a single-ended forward converter to achieve “true soft switching” The method includes injecting, with a current source and in transformer winding, a narrow pulse of current via an injection winding of the transformer to add such pulse to the magnetizing current to exceed the current level of current passing through freewheeling rectifier to reduce that current to zero time when the freewheeling rectifier is turns off at zero current conditions. Further, the sum of the magnetizing current and the injected current provide the current required by the output inductor during the transition time. The amplitude of injected current is defined such that the sum is greater than the minimum current through the output inductor (at least by an amount that reflects into the primary winding). The amount of current reflected in the primary is chosen to be sufficiently large to discharge parasitic capacitances reflected across the primary main switch to zero during the transition time.
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