A White LED Driver Based on Dual Mode Switch Dimming

A novel White Light Emitter Diodes (LED) driver based on dual mode switch dimming has been presented in this paper. The driver can automatically switch between Pulse Width Modulation (PWM) and Pulse Frequency Modulation (PFM) modes according to the dimming input signals. The PFM mode varies in a range of brightness from 0 to 50% and the PWM mode varies from 50% to 100%. In this way, the driver can achieve a high efficiency over a wide range of varied dimming and avoid color shift. At the same time, a Low Dropout Linear Voltage Regulator (LDO) is used as a compact and efficient power conversion circuit to ensure the stability of the output. The chip is simulated with CSMC 0.5 mum mixed signal models, and the results show that it possesses a 350 mA output current with the duty ratio changed from 0% to 100% to achieve constant luminance control. Its efficiency can always keep above 90% in all duty ratio of the control signals.