Advertisement
KRC-851D
CIRCUIT DESCRIPTION
7.5 V AVR
1C14:
M5237L
is the AVR
IC exclusive
for driver and
used in combination with the PNP transistor.
When
the power is turned ON, 041 turns ON to pull
the base of Q81 to turn 081 ON.
When
O81
turns
ON,
IC14
pulls the
base
of Q82
through R292.
The
collector
output voltage
of Q82
is divided
by
R292 and R293, then fed back to IC14.
IC14 compares
the above
voltage with the internal
reference
voltage and controls
the base voltage of
Q82 so that the returned voltage coincides with the
reference voltage.
C142 makes the rising edge of VCC when the power
is turned ON become gentle.
ACC Detection Circuit
IC15: PST529D-MT is used for power voltage surveilance.
ACC
voltage
is divided
by R306
and
R308,
and
voltage-limited
by D42,
then
applied
to terminal
|
(input) of IC15.
When the input voltage (terminal |) is dropped below
threshold
voltage
(approx, 8 V, when
converting
to
ACC voltage) of C15, terminal O (NPN, open collector)
turns ON (= low).
When
terminal O if IC5 is inverted to low, the emitter
of Q90 goes low and Q91 turns OFF, then Q92 turns
OFF.
Therefore, 1C12 pin (33): ACC | which is pulled down
by R310 goes low. That is, it is judged as ACC voitage
is at low level.
At the same time, IC4, 5 pin (4) STBY (standby) pin is
inverted to low via D44, and turns PWR
(power) IC
OFF, while the base of Q86
is pulled so that Audio
Muting (MUTE) is activated.
When
the ACC
voltage raises and the terminal
| of
IC15 exceeds the threshold voltage, the operation will
be reversed and it is judged as the ACC voltage is at
high level, while the PWR
(power) IC is turned ON
and Audio Mute is released.
(However, since Audio Mute is ORed with IC12 pin
(23) MUTE, audio muting will not be released immedi-
ately because of the latter MUTE, even
if the above
operation releases the MUTE)
vce
BACK
UP +8
POWER
ON
(LOW?)
GND
Vref: Internal reference voltage = 1.26 V
R309
1c 12@) Pwr
1c4,5
MUTE
Bu SV
ACC
+8
1ci2
ACCIN
Advertisement
