Keyboard Leds Driver; Display And Air Bubble Led Driver - Nokia NPL-4 Series Manual

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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 39 R is used to create the current limit with transistor Vbe volt-
age.
DLIGHT

Display and air bubble LED driver

LEDs are supplied from VLED voltage throught current limiting circuit. Display and air
bubble illumination is controlled by DLIGHT –line (UEMEK). BJT driver controls the con-
stant current generator.
- Driver will work as constant current generator increase or decrease the output voltage
for LEDs to keep the current stable. Serial resistance 33 R is used to create the current
limit with transistor Vbe voltage.
- Air bubble LED is located under the air bubble. Its current consumption will be ~3.8mA.
Copyright © 2005 Nokia Corporation. All rights reserved.
Issue 2 05/05
Figure 29: Keyboard Led Driver and Control Diagram
VLED
R=39Ω
System Module and User Interface
UI Board
NPL-4/5/
Page 69