A pair of back-to-back-coupled zener diodes is coupled from the input to the output of each leg of a common mode choke used in a LC circuit for reducing EMI into the power supply of an electrical device. The reversed biased zener diode of each pair breaks down when ringing voltage amplitude resulting from a voltage surge applied at the inputs of the common mode choke exceeds the breakdown threshold voltage of the zener diode. Transorb devices may be substituted for the back-to-back-coupled diode pairs.