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7. +5 V Line Constant Voltage Control Circuit
The +5 V line constant voltage control circuit is shown below.
Port 16 of IC51 (TL494CN) monitors the + 5 V line, and the voltage is compared with the standard voltage,
which is input into port 15. When the voltage of port 16 goes below 4.81 V or above 5.17 V, the pulse width
of the PWM signal, which is output from port 8, changes and the +5 V line is kept between 4.81 V to 5.17 V.
+5v Line
GND
R53
R88
R64
R65
+
IC51
TL494CN
D51
L51
8
R51
R61
Q51
-
16
15
+35V
R81
R59
R60
ZD55
GND
GND
Figure 2-29 +5 V Line Constant Voltage Control Circuit
FX-2170 Service Manual Operating Principles
Rev.A 2-21