An AC/DC converting circuit, has a full-bridge rectifier having two input terminals and two output terminals, a first capacitor, a second capacitor, an electronic switch having a control terminal, a trigger circuit having an input terminal and an output terminal, and a detecting circuit having an input terminal and an output terminal. The first capacitor and the second capacitor are serially connected between the output terminals of the full-bridge rectifier, the input terminals of the full-bridge rectifier are connected to an AC input, one end of the electronic switch is connected between the first capacitor and the second capacitor, the other end of the electronic switch is connected to one of the output terminals of the full-bridge rectifier, the input terminal and the output terminal of the detecting circuit are connected to the output terminals of the full-bridge rectifier, the output terminal of the detecting circuit is connected to an input terminal of the trigger circuit, and the output terminal of the trigger circuit is connected to the control terminal of the electronic switch.