Abstract: A constant current driver with a very low dropout voltage for the white light LED is designed. A 0.75V band-gap reference, based on the first order temperature compensation and resistive subdivision technology, is constructed in the chip. A 350mA constant driving current can be provided at the supply voltage from 2.7V to 7.0V. When temperature changes from -10℃ to 100℃, the variation in the output current is less than 5.06%. The driving current varies by less than ±0.8% when the supply voltage changes by ±10%. The dropout voltage of the power MOSFET is about 120mV. The power dissipation of the control circuit is less than 1.75mW, and the efficiency of the chip can reach up to 75%.

Key words: low dropout voltage, constant-current driving, band-gap reference, conversion efficiency