Device for driving LED and method for driving LED

A method for driving an LED, applied to a device for driving an LED, wherein the device for driving an LED comprises:

• a rectifier circuit, a capacitance-adjusting circuit, a control circuit and a DC-DC converter, wherein the capacitance-adjusting circuit comprises a first capacitor, a second capacitor and a switch, the first capacitor is electrically connected to the second capacitor, the switch is electrically connected to the second capacitor, the control circuit is electrically connected to a control terminal of the switch, the control circuit and the output terminal of the rectifier circuit are connected in parallel, the control circuit comprises a first resistor, a second resistor, a third resistor, a Zener diode and a first MOS transistor, wherein a first terminal of the first resistor is electrically connected to a positive pole of the output terminal of the rectifier circuit, a second terminal of the first resistor is electrically connected to a first terminal of the second resistor, a second terminal of the second resistor is electrically connected to a negative pole of the output terminal of the rectifier circuit, a first terminal of the third resistor is electrically connected to the positive pole of the output terminal of the rectifier circuit, a second terminal of the third resistor is electrically connected to a drain electrode of the first MOS transistor, a source electrode of the first MOS transistor is electrically connected to the negative pole of the output terminal of the rectifier circuit, an anode of the Zener diode is electrically connected to a gate electrode of the first MOS transistor, a cathode of the Zener diode is electrically connected to the second terminal of the first resistor, and the control terminal of the switch is electrically connected to a drain electrode of the first MOS transistor, and the method comprises:
• converting an input AC voltage into a first DC voltage by the rectifier circuit;
• converting the first DC voltage into a second DC voltage by the DC-DC converter, and outputting the second DC voltage to an LED load;
• and
• controlling the switch by the control circuit, to adjust a magnitude of a capacitance value of the capacitance-adjusting circuit,
• wherein a range of a voltage value of the AC voltage comprises a first AC voltage range and a second AC voltage range, and the first AC voltage range is lower than the second AC voltage range;
• when the voltage value of the AC voltage is in the first AC voltage range, the switch is controlled such that the capacitance-adjusting circuit has a first capacitance value;
• and when the voltage value of the AC voltage is in the second AC voltage range, the switch is controlled such that the capacitance-adjusting circuit has a second capacitance value, and the first capacitance value is greater than the second capacitance value.