Research Of Three-channel LED Constant Current Driver

With the rapid development of LED technology,it is increasingly applied in various fields,such as decorative lighting,automotive lighting and traffic lights.It can be expected that LED will become the primary light source in the future,because it has the advantages of high luminescence efficiency,environmental protection and long lifetime.In general,the multi-color LED light source consists of R(red)G(green)B(blue)three primary colors.In order to make the display more uniform,the input current of the LED should be as stable and uniform as possible.To gain the flexibility of the function including dimmer and the palette,the input current of the drive circuit must be able to be adjusted by controlling signal.In view of the above requirements,this paper studies a novel three-channel LED constant current driver chip,Compared to the current regulation scheme using an external resistance,the chip uses digital gate signal to control the gate circuit and adjusts the output current by changing the situation of the MOS in the structure of the current mirror,so the output current can be controlled more flexible.The chip analog system includes a bandgap reference module,low dropout linear regulator module,internal oscillator,power on reset module and constant current driver module.Among them,the starup circuit contained in bandgap reference module can rapidly reach the normal output voltage before the normal output voltage has not been established;Low dropout linear regulator module uses the operational transconductance amplifier with high output impedance to ensure the phase margin and improve the performance of the circuit;The dimming circuit is adopted in the constant current driver module,so this module can receive digital strobe signal.Based on Maxchip 0.18?m BCDMOS process,using Cadence spectre simulation software,The proposed simulation system each module of circuit and chip simulates features and the main performance.The simulation results show that the three channels of the chip meets the requirements of the series circuit of the numerous LED,and also meets the performance index and practical application requirements.Meanwhile,when the input voltage ranges from 3.5V to 6V and the temperature varies from-40? to 85?,the chip can output 16 level adjustable constant current from 4mA to 64 mA while each amplification is 4mA,and the maximum output withstand voltage is 24 V.