Siemens SXG 75 Service Repair Documentation page 53

11.1.4 Illumination
The LCD backlight is supplied by 4 white LEDs. These are connected in series to a high voltage
supply at 18.75V (VREG_BCKLT). The supply is generated by switching regulator N900, and is
enabled when BACKLIGHT_EN is high.
The current through the LED chain is set to 18mA using the current-limiter circuit of
V2200/R2222/R2225.
The backlight brightness is varied by turning the 18mA current on and off using a pulse-width
modulated switching signal LCD_BCKLT_PWM.
LCD backlight circuit
Technical Documentation
TD_Repair_L3_SXG75_R1.0.pdf
Company Confidential
2006©BenQ
Release 1.0
01/2006
Page 53 of 73