The Design Of Average Current Mode PWM Control High Efficiency Buck AC/DC LED Diver

White LED is with high luminous effciency, environment friendly and energy saving.It should work under constant current sitiation,so it needs to be provided with a current constant LED driver.To follow the requirement of the LED driver,this paper designed a chip with high effciency,high load regulation and good linearity regulation.This chip use Pusle Wildth Modulation way to make the Buck LED driver working at constant current every cycle and it adopt the Average Current Control mode.It use the Buck stucture to aviod using of tansformer,reducing the volume and the cost of the system.It use a simple way to direct sense the output current with an external resister,then sends the sampled voltage to the CS converter and the Error Amplifier,the output of the Error Amplifier is provided with an external Capacitor which compensate the whole feedback loop and to achive every cycle Average Current Control. This chip adopt single stage Power Factor Correction(PFC) circuit, using the Buck stucture as the PFC main control ciucuit,it can realize fast regulation of the output current and make the input current follow the input voltage.This paper utilize a new way to generate the rampe signal,this way use the sensed inductor current to integration for twice which increased the slope of the ramp signal and make the output current more accurate.The chip is made up of the following blocks,the PWM logic control block,which controls the shut off and turn on of the external power mosefet;the dirver block,which amply the drive capacity to turn on the external power mosefet;the protection block;the osillator provides 45 KHz pulse and with frequency jitter, frequency jitter can effectivelly reduce the Elctronic Magnetic Iterference of the circuit and inprove the Elctronic Magnetic Conpatiblity.The sub-circuits and the whole circuit are designde and verified by cadence softerware.And the Whole circuit is built and tested by 0.5um BCD process.The simulation and test results showed that the chip can work under 90~265V AC input,provid 200 mA constant current output,can achive power factor above 90% and constant current accuracy of 3%.