Robust LED backlight driver with low output voltage drop and hig output current accuracy

Constant current regulator for LED backlight system is more and more popular. Some methods are proposed to achieve low voltage drop on output power MOSFET. However, inaccurate output current due to channel length modulation or the oscillation phenomenon of the output current due to instability may occur. In this paper, we analyze the conventional LED driver and disclose the reasons causing the oscillation problem. Furthermore, a new robust circuit to drive LED strings is proposed to avoid the oscillation and to reach very low voltage drop on output power MOSFET. The efficiency of the driver is enhanced. When the output MOSFET is operated in the saturation region, the channel length modulation of the power MOSFET can also be alleviated and the sinking current remains constant as the drain-to source voltage varies.