Patent ID: 9237626
Filing Date: 2016-01-12
CPC Classification: H05B

Claim Text:
1. An AC dimming drive circuit for an LED, characterized by comprising: a rectification unit; and a first-stage LED DC drive circuit comprising a first voltage sampling unit, a first switch unit, and a first LED light source module; wherein the rectification unit receives an AC voltage, and rectifies the received AC voltage and outputs a DC voltage; the rectification unit outputs, through a first output terminal of the rectification unit, the output DC voltage to an input terminal of the first LED light source module and a first terminal of the first voltage sampling unit, an output terminal of the first LED light source module is coupled to a first input terminal of the first switch unit, a voltage division terminal of the first voltage sampling unit is coupled to a second input terminal of the first switch unit; and a second terminal of the first voltage sampling unit, an output terminal of the first switch unit, and a second output terminal of the rectification unit are grounded; the first switch unit receives, through the first LED light source module, a first switch-on voltage, and receives, though the voltage division terminal of the first voltage sampling unit, a first switch-off voltage; and when the first switch-on voltage rises to reach a first switch-on voltage threshold of the first switch unit, the first switch unit is conducted and the first LED light source module continuously emits light; and when the received first switch-off voltage rises to reach a first switch-off voltage threshold of the first switch unit, the first switch unit is switched off such that the first LED light source module stops emitting light; wherein the first switch unit comprises a third resistor, a fourth resistor and a fifth resistor, a first Zener diode and a second Zener diode, and a first field-effect transistor and a second field-effect transistor; wherein one terminal of the third resistor is coupled to the voltage division terminal; a negative terminal of the first Zener diode is coupled to the voltage division terminal, and a positive terminal of the first Zener diode is grounded; a gate of the first field-effect transistor is coupled to the other terminal of the third resistor, and a source of the first field-effect transistor is grounded; a drain of the first field-effect transistor, one terminal of the fourth resistor, one terminal of the fifth resistor, and a negative terminal of the second Zener diode are coupled to one another; the other terminal of the fifth resistor is coupled to a gate of the second field-effect transistor; and a drain of the second field-effect transistor, the other terminal of the fourth resistor, and a negative terminal of the first LED light source module are coupled to one another; and a positive terminal of the second Zener diode and a source of the second field-effect transistor are grounded.