Input ripple current cancellation technique resulting in less differential mode noise current

Switching current generated from the main switch in a switching converter injects a substantial amount of ripple current at the input side of the converter. The ripple current is undesirable, as it becomes an EMI noise source. Differential mode current traditionally need bulky and costly filtering components to suppress the first several harmonics down to an acceptable level. An alternative way to reduce the ripple, by means of nullification technique, is proposed. Both active and passive nullification approach are discussed in this paper. This technique results in smaller components size and reduced cost.