7. +5 V LineConstant Voltage Control Circuit
The+5 V line constant voltagecontrol circuit is shown below.
Port 16 ofIC51 (TL494C N) monitorsthe + 5 V line, andthe voltage is comparedwith thestanda rd voltage,
which is inputinto port 15.When the voltage of port16 goes below 4.81V or above 5.17 V,the pulse width
of thePWM signal, whichis output from port8, changes and the+5 V lineis kept between 4.81 V to5.17 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 ConstantVoltage Control Circuit
FX-2170 ServiceManual Operating Principles
Rev.A 2-21