Samsung SCH-2000, Service Manual, Page: 16 / 97

Circuit Description
4-6 Samsung Electronics
4-4 Hands-Free Kit
Hands-free board is largely composed of car
adapter circuit and Hands-free circuit.
4-4-1 Car Adapter Circuit
POWER SUPPLY
Input power switching circuit : This circuit (Q902,
Q903) is power switching control circuit. It supply
power for hands-free kit.
8V regulator (U806) : This circuit supplied power
for audio amplifier (+8V).
Vcc regulator (U807) : This circuit regulate Vcc
(+5V).
CHARGER CIRCUIT
This circuit charges battery pack by detecting the
temperature of battery, the slope of temperature,
the slope of the voltage of battery, charging time,
etc.
During charging time turns on red LED. Charging
is completed, turn on green LED.
Voltage detection circuit : Charging circuit is
designed to stop charging when the charging
circuit is decrease.
The voltage of battery is entered to A/D converter
located in U701 #4. (B/VTG)
Temperature detection circuit : The temperature
of battery is measured by missing NTC thermistor.
NTC thermistor has a characteristics of Log-scale.
It can obtain a linear characteristics by the parallel
connection of resistors.
4-4-2 Hands-free Circuit
POWER SUPPLY (U808)
U808 regulated -5V.
TX PATH
The audio signal from external Mic(J701) flows
into U802 #11. U802 include amplifier and Control
circuit for hands-free operating. U801A amplified
input signal. Output signal transmit to HHP.
RX PATH
Input audio signal canceled noise by difference
amplifier (U801c). U802 process hands-free action.
The RX audio signal is input (U805). The speaker
drive amp (U804) amplify the Rx audio signal and
the output of U804 is go out of speaker.
Battery Type Capacity Charge Time Charge Current
S t a n d a r d 1 0 0 0 m A H about 3h
°æ
3 0 M OA ~ 900mA
E x t e n d e d 1 6 0 0 m A H about 5h
°æ
3 0 M OA ~ 900mA