Silicon Controlled Rectifier (SCR) may be used as a controlled half wave rectifier unlike normal half wave rectifier. Figure 1 gives the basic circuit of Half Wave Controlled Rectifier using SCR. The AC voltage to be rectified is applied to the input of the power transformer. The voltage across the secondary winding feeds the anode to cathode circuit of an SCR through a load resistor RL. A dc voltage source drives a current through the gate of the SCR through a variable resistor R. The resistor R controls the gate current and thereby controls the rectified output dc voltage.