Power Supply Circuit; Comparator, Reduced Voltage - Icom IC-04A Service Manual

4-4
POWER
SUPPLY CIRCUIT
4-4-1
INTERNAL/EXTERNAL
POWER
SWITCHING
CIRCUIT (MAIN
UNIT)
When
using
an
attached
battery pack,
relay
RL101
is
OFF
and
POWER
SWITCH
R1
32
is
connected
to
the
bat-
tery pack.
When
a
power source with voltage
between
10-16V
is
connected to
EXTERNAL
DC POWER JACK
J203, RLl 01
is
ON
and R1
32
is
connected
to the exter-
nal
power
source.
In
case
a
wrong
connection
to
J203
is
made
with
reverse polarity.
Dll
7
is
reversely biased,
preventing
RLl 01 from
being
ON
and protecting the transceiver.
4-4-2
VOLTAGE REGULATOR
CIRCUITS
(MAIN UNIT)
A
three terminal voltage regulator (IC104) keeps the
output voltage
at
5V
constantly
even
when
input
voltage
is
from 5.1V
to 16V.
Noise
components
are eliminated
from the output of
IC104 through
a
filter circuit
consisting of
R165
and
C138. Output from
the
filter
circuit
is
fed to a current
amplifier
circuit
consisting of
0129
and 0130.
01 29
and
Q1 30
are
connected
in
a
complementary
cir-
cuit for
a higher current amplification factor.
The
base
voltage of
01 30
is
nearly equal to
the output voltage
of
1C
104. Also, the collector
voltage of
0129
is
approx-
imately
5V.
As
the
temperature
coefficient of
the
junc-
tion
voltage of
D1 14
is
nearly equal to the Vbe
of
01
30,
the output voltage
is
kept constant against
any change
in
temperature.
The
regulated
5V
from
the collector of
0129
is
fed to
common
circuits
through current
amplifier circuit
0114
and 0115, and
is
also fed to transmit/receive switching
circuit
0108
and
0109.
In
receive
mode,
pin
3
of
IC103
is
"LOW"
and
0108
is
turned
ON
to feed
R-i-
5 through current
amplifier
0110
and
01
1
1
.
At
this
time,
0109
is
turned OFF.
In
transmit
mode,
pin
3
of 1C
103
is
"HIGH"
and
pin
4
of
IC103
is
"LOW".
0108
is
turned
OFF
and
0109
ON.
Thus 01 09
feeds
T +
5 through
current amplifiers
0112
and
0113.
4-4-3
MPU POWER SOURCE
CIRCUIT
(MAIN UNIT)
When
the battery
pack
is
removed from
the transceiver,
a voltage
is
applied to
MPU
IC401
in
the
LOGIC UNIT
via
D1 19 from LITHIUM
BACKUP BATTERY
BT101
to
provide
backup
for
the
memory
contents.
4-4-4
VOX POWER
SOURCE
CIRCUITS
(PLL
UNIT)
The
current
limiter circuit
consists of
0219, D217,
R273, R274 and R275.
This
circuit
has
a
current
limit
of
maximum
5mA
and supplies a voltage to the optional
HS10SA
VOX
UNIT.
When
the current
is
overloaded
0219
reduces the
cur-
rent
until
the base voltage of
0219
plus
Vbe
and the
emitter voltage of
0219
are the
same.
R
+ 5 rs5
+5
r+5
4-5
COMPARATOR, REDUCED VOLTAGE
DETECTION CIRCUITS
4-5-1
COMPARATOR
CIRCUIT (MAIN
UNIT)
The voltage detected
in
the
S
meter
circuit
or
APC
cir-
cuit
is
input to pin
3
of
IC105A.
D/A
signals
from
the
MPU
are
fed
to pin
2 of
IC105A.
The
MPU
counts up and outputs
4
bit digital
signals un-
til
pin
2 of
IC105A becomes
higher
than
pin 3.
These
signals are
converted
to
an analog
signal
with
R409
R412
in
the
LOGIC
UNIT.
The
signals are divided at
R166
and
R179
in
the
MAIN UNIT
and changed
to
16
step
D/A
signals
between 0.12V and 1.258V.
When
the voltage
at pin
2 of 1C
105
A
is
higher
than
pin
3,
the output
at pin
1
is
"LOW"
and
applied to
the
MPU
as the
COMP
signal.
The
MPU
indicates
the counting
number
to
the S/RF
INDICATOR
as the
signal
strength
in
receive
mode
and
as
RF
output
power
in
transmit
mode.
4-5