Multi-channel constant current LED driver with temperature and voltage compensation

This paper proposes a new circuit for obtaining a constant current in parallel LED (Light Emitting Diodes) strings. This new technique not only achieves high invariability to temperature in each string but also reduces the internal and external resistance requirements. In this work, the LED current has a low correlation to its forward voltage (VF). Furthermore, this circuit matches the current of a multi-LED parallel string and maintains its accuracy by using only operational amplifiers to control these LEDs. In other words, it reduces the power consumption and die size considerably. The I
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obtained in this circuit is nearly independent of the temperature. This has been accomplished by the mutual compensation of mobility and threshold voltage variations. Moreover, the variations due to the temperature coefficient of resistance have been taken care of. The temperature coefficient of this circuit can achieve as low as 142ppm/°C over the range from -40-120/°C which large than 20mA.