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TK-3140
11
CIRCUIT DESCRIPTION
8. Power Supply Circuit
BB is supplied via a 3A fuse from the battery terminal
connected to the TX-RX unit. After passing through the power
switch, power supply (SB) is applied to the three AVRs. IC5
supplies 5V (5M) to the control circuit, and IC9 supplies 5V
(5C) to common circuits. IC6 supplies to the TX circuit, the RX
circuit and common circuits of needless save mode. During
transmission, 5TC becomes Low and Q3 is turned ON to supply
5V (5T) to the TX circuit. During reception, 5RC becomes Low
and Q2 is turned ON to supply 5V (5R) to the RX Circuit.
The power supply voltage monitor IC (IC404) monitors power
supply voltage (SB). If the voltage falls (less than 5V), the VOUT
port goes “LOW” level, the CPU INT port also goes “LOW”
level, and the CPU stops.
Fig. 15 Power supply circuit
Q404
5RC
5TC
5R
5T
5CNS
IC402
CE
IC403
CE
IC401
IC404
Q405
RF power amp (Q103 and Q106)
+B
F400
SB D405
ON/OFF
VOL
5C
14
VCC
RESET
INT
10
71
R740
IC400
IC309
CPU
R403
C425