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8. Power Consumption
Saving Circuit
This chassis employs the interval oscillation circuit on the power circuit for saving the con-
sumption of power supply circuit during the stand-by mode
The interval oscillation circuit consists of Q685, Q686, D685 and peripheral circuit. Q685
and Q686 drives the photo-coupler
D615 and oscillation of power circuit according to volt-
age level on point (A) in the figure. During power-on mode, the voltage on point (A) is
almost OV and Q685 and Q686 maintain turning-off.
When the set switches into stand-by mode, the voltage on point (A) increases about 15V.
The voltage which is divided with R688 and R687 is applied to Q685-base
and drives Q685
and Q686 turning-on.
When Q686 turns on, the photo-diode/transistor
in D61 5 is completely
turned on, then Q612 is turned on and Q613 is turned off. By this means, the oscillation of
.
power circuit stops and the voltage of secondary power supply falls down. Also the voltage
of point (A) falls down from 15V gradually.
When the voltage on Q685-base
is less than voltage of Q685-emitter,
Q685 is turned off
and then Q686 is off, then D615 and Q612 are turned off. Finally Q613 starts the oscillation
and the voltages are supplied to the secondary circuit. By this means, the voltage on point
\
(A) rises up and drives Q685 on again. By repeating the above operation, the power con-
sumption in the stand-by mode can be saved.
I
h
P
D615
R615
L
,
,
-1
T611
Q613
Q612
Oscillation stage
Output stage
Q684
R684
10k
To stand-by
drive circuit
h
R689
22k
Q685
R688
10k
R687
Q686
560k
D685
6.2V
Zb
Power-on
1
Stand-by
I
15V
Voltage deviation
of point@
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.........-
-—-—-—-
">......
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1
Ov
la
n
Operating
period of power circuit
-27-
Training
Manual
AC 1Chassis
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