A Fast Switching Current Regulator Using Slewing Time Reduction Method for High Dimming Ratio of LED Backlight Drivers

Abstract

This brief proposes a fast switching current regulator to achieve a high dimming ratio of the light-emitting diode (LED) backlight drivers. The proposed current regulator employs the slewing time reduction method to enhance the dimming ratio by decreasing the rising time of the LED forward current. A six-channel LED backlight driver was fabricated using a 0.35-mu m bipolar-CMOS-DMOS process technology which includes an n-type MOSFET with a low voltage of 5 V and a high-side lateral double diffused MOSFET with a breakdown voltage of 60 V. The measured rising time and minimum pulsewidth of the LED forward current are reduced to 4.8 ns and 12 ns, respectively, at a current transition of 60 mA. Consequently, the dimming ratio of the LED backlight driver using the proposed current regulator is calculated to be 160 000 : 1 at a dimming frequency of 500 Hz, which is more than three times higher than that obtained using the previously reported current regulators. Therefore, the proposed current regulator is suitable for high-end displays which require high image quality.