A High Precision Constant Current Source Applied in LED Driver

LED is generally driven by constant current because the color and brightness of LED are directly related to their forward current. The current accuracy is a very important index for a high performance LED driver. In this paper, a constant current source applied in LED driver is proposed to improve the accuracy of the LED current. The constant current source consists of a reference current generator, a current mirror and a current regulator. An accurate current mirror with high impedance is utilized which eliminates the channel length modulation effect of the MOSFETs. A new current regulator in which MOSFET operates in linear region instead of saturation region is proposed to improve the current accuracy and the driver´s efficiency. The proposed circuit is based on chartered 0.35μm 3.3/5 V process and has been simulated by Cadence spectre. The output current is 150 mA. Simulation results show that current accuracy of +/-0.5% for a wide output voltage range from 0.35 V to 13 V is obtained.