A double-loop control LED backlight driver IC for medium-sized LCDs

Light-emitting diodes (LEDs) are used as an alternative to the cold cathode fluorescent lamp (CCFL) for LCD backlight units (BLU) for their lower power consumption, wider color gamut, and better dimming capability, in addition to being mercury-free [1, 2]. Recently, various studies have focused on low-power solutions using LED BLUs in a multi-channel LED configuration [1-3]. While these methods effectively reduce power consumption of LED drivers with the phase-shifted backlight driving method [1], the transient response of the LED forward current is limited by the transient response of the boost converter in the LED driver IC. This makes it difficult to obtain a higher PWM dimming frequency than 1kHz in the LED BLU. In addition, the slow transition time of the LED current limits the minimum duty cycle and PWM dimming resolution. These problems generate audible noise and negatively affect the contrast ratio and power consumption of LCDs. To overcome these problems, we use an adaptive boost voltage with a double-loop control method. Here, the transient response of the LED current depends only on the transient response of the current regulator, which is significantly faster than that of the boost converter. ��2010 IEEE