Kenwood TH-D72A Service Manual page 8

TH-D72A/D72E
5-3. Lock voltage
The pulse signal obtained by the phase comparison in
each PLL IC (IC431, IC513) is sweep-output with the built-in
charge-pump. After removing the ripple with the loop-fi lter,
it controls the oscillator frequency as a control voltage of
each VCO.
Q357
A band
x3
2nd Local
X431
Main
IC737
MCU
REF_A
Volume
REF_B
IC721
&TC
X511
6. Power Supply Circuit
6-1. DC-IN circuit
The DC-DC IC (IC644) operates according to the control
signal from the Reset IC (IC639) when the power supply is
supplied to the DC-IN JACK, and +B voltage is obtained. +B
voltage changes with the DC switch (Q663) controlled with
the Sub MCU (IC611), and obtains 10.8V (reception) and 8.0V
(transmission).
6-2. Lithium-ion battery charging control circuit
When the power supply is supplied to the DC-IN JACK
with the Lithium-ion battery installed, the charge processing
is done to the Lithium-ion battery.
The main MCU (IC737) recognizes that the DC switch
(Q642) becomes "L" level when the power supply is sup-
plied to the DC-IN JACK, and assumes the gate of the DC
switch (Q648) to be "H" level, and it is turned on. If the
comparator IC (IC641) is "L" level (approximately 8.4V or
less) at this time, the DC switch (Q646) is turned on. As a
result, a constant voltage of about 1.5V is impressed from
the regulator IC (IC643) to the base of the DC switch (Q643),
the current between the collector-emitter becomes con-
stant, and the current that fl ows to the Lithium-ion battery is
constantly controlled.
Moreover, the current is switched by turning the DC
switch (Q653) on and off according to the voltage of the
Lithium-ion battery, and the charge is switched preliminary
8
CIRCUIT DESCRIPTION
D432,D433
IC431
1/R PD 1/N
A band PLL IC
LDA
Sub
IC611
MCU
LDB
D523,D524
E-
Mod
D514,D515
IC513
1/R PD 1/N
B band PLL IC
Figure 4 VCO-PLL circuit
5-4. Unlock detection circuit
The terminal LD (pin 14) of each PLL IC (IC431, IC513)
outputs the "L" level at the Unlock statement. The main
MCU (IC737) observes this, and controls the change timing
of transmission, reception, etc.
Q435 Q436 Q437
Q434
Q522
Q201
Q523
D203
Q524
RF
SW
Q521
and usually charge (preliminary charged in 6V or less). The
voltage detection of the Lithium-ion battery has gone by
the differential amplification by OP-Amplifier (IC642). The
sub MCU (IC611) is protected from the detecting voltage at
Power-off with the DC switch (Q662).
Normally, when pin 5 of the comparator IC (IC641) be-
comes "H" level (approximately 8.4V or more), the DC
switch (Q646) is turned off, and it changes into the charging
status in the constant voltage because the base voltage of
the DC switch (Q643) is not stable. The emitter voltage of
the DC switch (Q643) is observed by the sub MCU (IC611)
so that the current may decrease gradually in the constant
voltage charge. When the threshold is exceeded, the DC
switch (Q648) is turned off and the charge is stopped.
6-3. Protection circuit
The environmental temperature detected with the
Thermistor (TH703) is observed with the Main MCU (IC737),
and the DC switch (Q648) is assumed turned off, and the
charge is stopped when it is out of the temperature range
(0°C≤Temp.≤45°C).
When the excess voltage is impressed from the DC-IN
JACK, the circuit is protected by intercepting the power sup-
ply with the DC switches (Q649, Q645).
Moreover, power consumption is reduced by intercept-
ing the DC switches (Q651, Q652) according to the SAVE1
signal from the Sub MCU (IC611) while in save mode.
D6
VHF
RF
A band
SW
1st Local
UHF
RF
A band
x2
SW
1st Local
D437 Q438
TX
D5
VHF
RF
B band
SW
1st Local
UHF
RF
B band
SW
1st Local
Q204 D7