(a) Natural Commutation
When the anode current is reduced below the level of the holding current, the SCR turns off. However, it must be noted that rated anode current is usually larger than 1,000 times the holding value. Since the anode voltage remains positive with respect to the cathode in a dc circuit, the anode current can only be reduced by opening the line switch S, increasing the load impedance RL or shunting part of the load current through a circuit parallel to the SCR, i.e. short-circuiting the device.