Isolated current doubler with multiple levels of ripple cancellation

A new ripple-cancellation structure for a switch-mode power converter using a current doubler is described. Three refinements of an isolated current-doubler rectifier topology produce a very low level of output ripple without compromising power conversion efficiency. One refinement selects the turns ratio of the current doubler magnetics as a function of the nominal switching duty cycle to eliminate output current discontinuities. A second selects the magnetizing inductances to produce matched magnetizing current slopes, which produces a ldquoflatrdquo output current pulse. A third utilizes ldquocancellationrdquo of residual output ripple current by injecting a mirror image of the residual ripple current into the output capacitor based on a voltage difference between windings of the magnetics. With these multiple levels of ripple cancellation, a very low level of output ripple is produced without compromising power conversion efficiency.