A novel DC and PWM dual-mode dimming circuit for the WLED driver

It is very important for a light source that the brightness could be adjusted conveniently. A novel DC and PWM dual-mode dimming circuit for a monolithic WLED driver is proposed for the first time in this paper. It can alter flexibly the control mode between the analog (DC) and digital (PWM) dimming according to the input control signal. In the DC dimming mode, when the input DC control voltage is adjusted from 0.5V to 2.5 V, the average output current can be changed from 20% to 100% of the nominal current value. While in the PWM dimming mode, the output current is proportional to the duty cycle of the input PWM signal and changed from about 0% to 100% of the nominal current value. The WLED driver with the proposed dual-mode dimming circuit has been verified in a 0.5 mu m HVCMOS process, and the nominal value could be set more than 1 A by the external resistors.