A powering circuit of an AC-DC converter, for converting a AC input voltage from an AC power supply into a DC output voltage, comprising: a rectifier, having a primary side coupled to the AC power supply and a secondary side for outputting a DC power supply; a sensing circuit, having a voltage divider and a first switch, wherein the first switch comprises a control pad, an input pad, and an output pad, the output pad is connected to ground potential, the voltage divider is coupled to the secondary side of the rectifier so as to obtain a divided DC voltage of the DC power supply at the secondary side and connect the divided DC voltage to the control pad of the first switch, for turning off the first switch when the divided DC voltage is lower than a turn-on voltage of the first switch, the divided DC voltage determines whether the first switch is turned on or not; a control switching circuit, having a third resistor, a first zener diode, and a second switch, wherein the second switch has a control pad, an input pad, and an output pad, the third resistor is connected at one end to the secondary side of the rectifier and at the other end to the input pad of the first switch and a cathode of the first zener diode, an anode of the first zener diode is connected to ground potential, the control pad of the second switch is connected to the input pad of the first switch and the cathode of the first zener diode, the input pad of the second switch is connected to the secondary side of the rectifier, and the output pad of the second switch is connected to a DC output end, for turning on the second switch when the DC voltage of the DC power supply at the secondary side of the rectifier is lower than a preset reference voltage (Vref), and turning off the second switch when the DC voltage of the DC power supply at the secondary side of the rectifier is higher than the preset reference voltage (Vref), when the first switch is turned off, the second switch is turned on and the DC output end outputs a low DC output voltage; and a voltage regulating capacitor, being connected at one end to the output pad of the second switch and the other end to ground potential, characterised in that the circuit further comprises a second zener diode) having a cathode connected to the control pad of the first switch and an anode connected to ground potential, for clamping a voltage level of the first switch. a rectifier, having a primary side coupled to the AC power supply and a secondary side for outputting a DC power supply; a sensing circuit, having a voltage divider and a first switch, wherein the first switch comprises a control pad, an input pad, and an output pad, the output pad is connected to ground potential, the voltage divider is coupled to the secondary side of the rectifier so as to obtain a divided DC voltage of the DC power supply at the secondary side and connect the divided DC voltage to the control pad of the first switch, for turning off the first switch when the divided DC voltage is lower than a turn-on voltage of the first switch, the divided DC voltage determines whether the first switch is turned on or not; a control switching circuit, having a third resistor, a first zener diode, and a second switch, wherein the second switch has a control pad, an input pad, and an output pad, the third resistor is connected at one end to the secondary side of the rectifier and at the other end to the input pad of the first switch and a cathode of the first zener diode, an anode of the first zener diode is connected to ground potential, the control pad of the second switch is connected to the input pad of the first switch and the cathode of the first zener diode, the input pad of the second switch is connected to the secondary side of the rectifier, and the output pad of the second switch is connected to a DC output end, for turning on the second switch when the DC voltage of the DC power supply at the secondary side of the rectifier is lower than a preset reference voltage (Vref), and turning off the second switch when the DC voltage of the DC power supply at the secondary side of the rectifier is higher than the preset reference voltage (Vref), when the first switch is turned off, the second switch is turned on and the DC output end outputs a low DC output voltage; and a voltage regulating capacitor, being connected at one end to the output pad of the second switch and the other end to ground potential, characterised in that the circuit further comprises a second zener diode) having a cathode connected to the control pad of the first switch and an anode connected to ground potential, for clamping a voltage level of the first switch.