Patent ID: 8253342

Claim:
An LED illumination system comprising: an LED lamp comprising an LED string which has a plurality of LEDs connected in series; a voltage stabilizing circuit connected to the LED lamp for supplying an electric current to the LED string; and a control circuit comprising a micro-programmed control unit and a MOSFET connected between the micro-programmed control unit and the LED string, the micro-programmed control unit detecting the electric current flowing through the LED string and outputting a PWM signal which has a frequency within a range from 60 Hz to 500 Hz to the MOSFET, the MOSFET receiving the PWM signal from the micro-programmed control unit and turning on and off repeatedly under a control of the PWM signal, making a flicker frequency of the LEDs of the LED string be within a predetermined range; wherein the MOSFET is a N-channel enhancement mode MOSFET, the micro-programmed control unit comprising a control terminal connected to a gate of the MOSFET, a drain of the MOSFET being connected to a negative pole of the LED string, a source of the MOSFET being connected to the ground via a current detecting resistor, the PWM signal being outputted by the control terminal; wherein a junction is formed between the current detecting resistor and the source of the MOSFET, the micro-programmed control unit further comprising a comparing terminal connected to the junction, the micro-programmed control unit setting a reference voltage therein, the micro-programmed control unit comparing a voltage of the comparing terminal with the reference voltage and outputting different PWM signals which have different frequencies to the MOSFET according to a compared result, thereby changing an internal resistance of the MOSFET after the MOSFET has been turned on; and wherein the micro-programmed control unit comprises a feedback terminal connected to the voltage stabilizing circuit, the micro-programmed control unit detecting the electric current flowing through the LED string and outputting a feedback signal to the voltage stabilizing circuit, to control the voltage stabilizing circuit to output a predetermined voltage to the LED lamp, the micro-programmed control unit compares the voltages of a first, a second and a third comparing terminal with a reference voltage, and outputs different PWM signals to a first, a second and a third MOSFET via a first, a second and a third control terminal, thereby to control a flickering frequency of each of the first, second and third LED string within a predetermined range.