Patent ID: 6865094

Claim:
A circuit, comprising: a rectifier bridge for rectifying an AC voltage from an AC power supply; a conversion circuit coupled to the rectifier bridge for converting the rectified AC voltage to a DC voltage, the conversion circuit comprising: a transformer comprising a primary winding and a secondary winding, a pulse width modulator (PWM) coupled to the primary winding, and a switching transistor, wherein a gate of the switching transistor is coupled to the PWM and a drain of the switching transistor is coupled to the primary winding; an opto-coupler coupled to the conversion circuit for monitoring an output connection coupled to the secondary winding, wherein the opto-coupler comprises: a diode, wherein an anode of the diode is coupled to the PWM and the switching transistor, and a cathode of the diode is coupled to the secondary winding, and a transistor coupled to the diode and the PWM, wherein when a system is not coupled to the output connection, an AC ground current flows through the diode, wherein the transistor is turned on, wherein the PWM and the switching transistor are turned off, such that the AC voltage is substantially prevented from being drawn from the AC power supply.