Fixed-frequency adaptive off-time controlled buck current regulator with excellent pulse-width modulation and analogue dimming for light-emitting diode driving applications

This study presents an ideal synchronous buck current regulator for variety of light-emitting diode (LED) loads from wide input voltage range. By using high-side power switch matched sense, the regulator maintains high current accuracy and high system efficiency. The adjustable current sense threshold provides a full-range analogue dimming and the fast output enable/disable function allows for high-frequency pulse-width modulation (PWM) dimming. In addition, the two dimming methods are easy to implement and have highly linear range. An adaptive off-time control is adopted to regulate an accurate constant current for its fast response and no need for control loop compensation, while its disadvantage of variation of switching frequency is overcome. The proposed circuit has been fabricated with 0.35 μm 40 V bipolar-CMOS-DMOS (BCD) process successfully. The experimental results confirm that the LED driver can operate within 6-40 V input voltage, and can drive a 1-10 output series connected LEDs. The switching frequency is fixed at 500 kHz with a variation of ±2%. The measured system peak efficiency is up to 95% at 1 A LED current and 10 V output voltage. The settling time at the PWM rising edge is <;3.5 μs which is well beneficial for fast PWM dimming.