Patent ID: 7429832

Claim:
A light control circuit for use in light control fluorescent lamps comprises a filter and rectifier circuit ( 1 ) with its input coupled to an AC power supply; a frequency control and resonant circuit ( 2 ) with its input coupled to output of the filter and rectifier circuit ( 1 ); an ambient brightness signal sampling and control circuit ( 4 ) with its input coupled to the output of the filter and rectifier circuit ( 1 ) while its output being coupled to the frequency control and resonant circuit ( 2 ); the ambient brightness signal sampling and control circuit ( 4 ) includes a programmable integrated circuit (U 1 ), and a resistor (R 1 ) serially connected to a capacitor (C 3 ) in shunt connection with a polarized capacitor (C 2 ) and a zener diode (Z 1 ) between a positive input and a negative input of the ambient brightness signal sampling and control circuit ( 4 ); wherein a power supply pin (VDD) of the integrated circuit (U 1 ) is coupled to a connection point between the resistor (R 1 ) and the capacitor (C 3 ), and a ground pin (GND) of the integrated circuit (U 1 ) and the negative input being grounded together; characterized in that: the integrated circuit (U 1 ) of the ambient brightness signal sampling and control circuit ( 4 ) comprises at least one input pin (GP 0 , GP 2 ), an output pin (GP 1 ) and a specific program for controlling working mode of the light control circuit; the ambient brightness signal sampling and control circuit ( 4 ) further comprises: a photosensitive element in shunt connection with a capacitor (C 4 , C 6 ) being respectively connected between the at least one input pin (GP 0 , GP 2 ) and the negative input; a resistor (R 2 , R 3 ) respectively connected between the at least one input pin (GP 0 , GP 2 ) and the power supply pin (VDD); and a resistor (R 5 ) connected to the output pin (GP 1 ) at one end and coupled to a gate of a thyristor (Q 3 ) at another end, and a resistor (R 4 ) and a capacitor (C 11 ) being in shunt connection between the gate and a cathode of the thyristor (Q 3 ); and the cathode of the thyristor (Q 3 ) is further connected to the negative input.