High-efficiency, high-dimming ratio LED driver

A high-efficiency, high-dimming ratio LED driver, capable of driving two standard white LEDs in series, is presented in this paper. A synchronous boost converter with on-chip switches and PWM controller is used as the LED driver. The LED current is sensed using voltage-mode feedback to maintain a constant load current. The output sense resistor in a conventional LED driver is replaced by the disconnect switch with an equivalent on-resistance to increase efficiency. Lossless current-mode feedback, in which the inductor current is sensed via the on-resistance of the boost series switch, is used to improve stability. Dimming control logic is implemented with a 10-bit counter and a 10-to-1 MUX, generating 10 dimming ratios ranging from 2:1 at a frequency of 625 kHz to 1024:1 at 610 Hz. The simulated efficiency of the LED driver alone is 86.1% and that of the LED driver with dimming control is 85.4%.