Over Current And Overload Detection; Detection Of Dc Voltage - Pioneer QX-949A Series Service Manual

Over-current and Overload
Detection
The equivalent circuit of
this detector
section
is
shown
in
Fig. 23, andFig.
24 shows the equivalent
circuit at the time of
a positive half
cycle.
When
this equivalent circuit
is overloaded, the
balance
of
the
bridge, formed
by
REI-, R1, Rg and RL,
is
disturbed, and a potential is produced between
b
and
a
in
such
a
direction that Q1 is turned
on.
When
Q1
is
turned
oo, the
collector- current
increases,
the relay driving circuit
functions
and
the relay switch of the output circuit
is
turned off.
After the
cause
of
the
overload
is
removed, the
bias
of
Q1 is reduced and the relay switch turns
on to
automatically restore normal
operation,
Fig. 25
shows
the
equivalent
circuit at the
time
of
a
negative
half
cycle.
In
this circuit a potentiat
is
produced between
b
and
e
as above, and
Q1
is
turned
on.
Detection of
DC Voltage
This
is
a
differential amplifier consisting
of
Qb
and Q6,
as shown
in
Fig. 26. The
bases
of
Qb
and Q6 are
connected
to
the
junction-points of
the power amplifiers.
When
the DC
balance
of
the
power
stage
is lost
for
some reason, a
potential
difference
is
produced
in
the input
signal
to
the
differential amplifier, and the collector currents of
Q5 and
QG
are
put out of
balance.
Thus, the relay
driving circuit functions, and the relay switch
is
turned off.
Glx-g4slA
Fig.23
Fig.24
Fis.25
Power
Amplifier
Relay driving circuit
Relay driving circuit
r______
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Fis.26