Patent ID: 7940090

Claim:
A zero-crossing detecting device that detects a zero-crossing point of AC voltage, the device comprising: a full-wave rectifier that rectifies the AC voltage and outputs a current based on a full-wave rectified voltage; a charger, which includes a diode and a capacitor, wherein the capacitor is charged by the current and has a saturation voltage near the zero-crossing point, and the capacitor outputs a charging current when the full-wave rectified voltage falls below the saturation voltage, and wherein the diode prevents the charging current from flowing back into the full-wave rectifier; a signal output part that outputs a zero-crossing detecting signal, wherein the signal output part outputs the zero-crossing detecting signal when the charging current flows to the signal output part; and a gate part, which that prevents the current output from the full-wave rectifier from flowing into the signal output part, wherein the diode, the signal output part and the gate part are connected circularly, the signal output part is arranged between the diode and the gate part, the diode and the gate part are connected to the full-wave rectifier, one side of the capacitor is connected to a location between the diode and the signal output part and an opposite side of the capacitor is connected to ground.