An AC to DC circuit includes a rectifier circuit, a voltage detecting circuit, the current source and the output circuit. The rectifier circuit converts the AC power to pulsating DC. The constant current source provides current to the voltage detection circuit and to the control port of the output circuit. The current passing throughout the constant current source is the sum of the current flowing to the voltage detection circuit and to the output circuit. The voltage detection circuit increases with the instantaneous value of the output voltage of the rectifier circuit, it absorbs more current from the current provided by the constant current source and less current flows from the constant current source to the control port of the output circuit. The output circuit amplifies the current of the control port and outputs it to power the load. The AC to DC circuit of the present invention can rectify the portion of an alternating input voltage below a sine peak of the alternating current, working at a sine wave ascending area and a sine wave descending area, and it can carry a capacitive load.