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8-30
8.2 Power Board
8.2.1 Power Supply Assembly
(2) The LCD (VDD, VEE)
(3) The backlight (CCFT)
1. Charge control circuit
The power controller 87C51 can detect the battery whe-
ther charging is completed (charge LED off) by sensing
the battery voltage. It is because, after battery is fully
charged, further charging will cause the reduction of its
voltage.
2. Voltage detector
The 87C51 reads the voltage of main battery, +5V from
ADC0833 and manages the power of the whole system.
nerate 5V, send PG (POWER GOOD) signal for main
board, and light up green power LED.
to battery low mode. Under thismode, the buzzer will
beep twice every 15 seconds. Upon using battery and the
output voltage being lower than 4.5V, it will change to bat-
a
. Power supply circuit
The transformer can transform the input voltage 5.0V to
15V, which supports the MOSFET as bias voltage. The
output MOSFET is regulated to 5V.
. Power supply of LCD circuit
It generates VDD and VEE for LCD when the signal
Py
VEE depends on the signal from keyboard controller
87C51 on the main board. When the duty of the signal in-
creases, the VEE de-creases.
5. Power Supply for Backlight (CCFT)
jt generates VBL for CCFT when the signal BLE is low.
The circuit uses VSW to generate VBL. The VBL de-
pends on the signal from keyboard controller 87C51 on
the main board. When the duty of the sigan! increases,
the VBL increase.
CS 55 846
8.2.2
Connector pin assignment
CN1 4-pin Voltage Adapter connector
Pin.no
Signal
1
VA
2
VB
3
POK
4
GND
J2 2-pin battery connector
Pin.no
Signal
1
+VM
2
GND
J3 5-pin backlight connector
Pin.no
Signal
VCFF (AC)
anon
z oO
VCFF (AC)
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