Kenwood TK-250 Service Manual page 21

TK-250
CIRCUIT DESCRIPTION
6. POWER SUPPL Y CIRCUIT
6.1 Power switching
A 5V reference voltage is derived from an external power
supply or internal battery by IC1. This reference is used to
provide a 5V supply in transmit mode [5T] , and a 5V supply
in receive mode [5R] and a 5V supply common in both modes
[5C] and [5SV] based on the control signal se nt from the
microprocessor or shift register. IC203 and IC204 in the con-
trol unit provide a 5V supply for the control and display cir-
cuits .
6.2 Battery sa ver
If no activity is detected(squelch closed) on the channel,
the units enters into the battery save mode controiled by the
microprocessor and shift registor. In this mode, SAVE line is
set low, causing Q4 to disable [5SV].
5T
CV)
o
5SV(VCO)
5R
Q4
I
DC SW
I
Q7
0)
cr:
t~
Q5
([)
cr:
KEY(APC)
..,.
cr:
..,.
'"
ü
5SV
'"
'"
SAV
ü
1
I
DC SW
I
T/R
r-- 1+
Ü
IAVR
I
I Cl
SB
TX-RX section
Power supply
SB
+1
co
CV)
N
Ü
Fig.7 Power supply circuit
(Power switching, battery saver)
21