An auxiliary converter circuit for regulating an input current to a main switching converter circuit. The auxiliary converter circuit has a voltage detector for determining a change in a voltage across the auxiliary converter circuit, and a current sensor for sensing an input current to the main switching converter circuit. The auxiliary converter circuit also has a current compensation circuit that includes a comparator circuit arranged to compare the sensed input current with a reference current; and a controlled current circuit. The controlled current circuit is arranged to selectively provide a positive compensation current and a negative compensation current to the input current, based on the determined voltage change and the comparison, for suppressing harmonic distortion and electromagnetic interference in the input current.