The present invention provides a circuit for generating a control voltage depending on voltage phase of an input signal. The circuit comprises a first transistor; a second transistor, a diode, a Zener diode and a capacitor. Base and collector of first transistor along with collector of second transistor are connected to a DC voltage source. Anode of the diode is connected to base of the first transistor and cathode of the diode receives the input signal. Anode of the Zener diode is connected to the base of the second transistor and cathode of the Zener diode connected to the collector of the first transistor. The capacitor is connected between cathode of the Zener diode and ground terminal. During positive half cycle and negative half of input signal, the circuit outputs a high control voltage and a low control voltage respectively.