User Guide

NPL-4/5

System Module and User Interface Nokia Customer Care

Power supply for LEDs

DC/DC converter generates VLED supply voltage for white LEDs. There are two white LEDs

connected series in display and on keypad PWB in four branches. The flashlight has one

white LED. Feedback resistors R300, R302 and R310 set output voltage. The voltage ref-

erence is 0.515V inside the driver.

Driver is controlled by the UEMEK via CALLED1 output. This signal is connected to driver

EN-pin (on/off). R317 is used to increase converter output current.

Figure 28: VLED Voltage Supply

Keyboard LEDs driver

LEDs are supplied from VLED voltage throught current limiting circuit. Keyboard illumi-

nation is controlled by DLIGHT –line (UEMEK). BJT driver controls the constant current

generator. DLIGHT line needs voltage matching for higher VLED voltage than battery

voltage. Control line has capability to dimming. The DLIGHT line is common for display

and keypad illumination driving.

Driver will work as constant current genertor increase or decrease the output voltage for

LEDs to keep the current stable. This means that constant current flow through each

branch. Serial resistance 39R is used to create the current limit with transistor Vbe volt-

age.

CALLED