3. +35 V ConstantVoltage Control Circuit
The+35 V constan t voltagecontrol circuit is illustratedbelow.
The constant voltage control circuit operates to keep the 35 V line at 35 V ±6 %. When the voltage between
ZD51 and ZD85 becomes 32.7 V ±2.75 %,PC1 turns on,and then Q2also turns on.Consequently, switching
FET Q1 shuts off. When the voltage between ZD51 and ZD85 becomes less than 32.7 ±2.75 V, PC1 turns
off, and then Q2 also turns off. Consequently, switching FET Q1 operates again. Repeating the above
operation keeps the +35 V lineat 35 V±6%.
4. +35V LineOver load Detection Circuit
The+35 V line voltage drop protectioncircuit is shown in the figurebelow.
When the+35 V line is overloaded,it means that constant voltagecontrol isnot being maintained. In this
condition, theforward currentof PC1 drops to 0 A. Consequently,voltage Vf between PC1 andD81 also
drops. On this circuit,when the Vf voltagedrops below 1.3 V (+35 V line: 33.1 V), IC528 detects the
overload and outputsthe PWDNsignal (+5 V: HIGH active) to port 20 of theCPU. When the CPU receives
this PWDN signal,printing stops.When the +35 V line becomes normalagain, the voltage betweenPC1 and
D81 alsobeco mes normal. When theVf voltage goesabove 1.6 V (+35V line: 33.4 V), thePWDN signal is
removed.
+35V Line
ZD81
ZD51
ZD82
ZD83
ZD84
ZD85
D81
R56
R57
GND Line
9+
10+
11
R11C13
Q3
R14 C12 +
Q1
1
2
8
7
R20 R21
R19
C15
Q2
R13
R15
R16
IC1
Figure 2-25 +35 VLine Constant Voltage Control Circuit
+35V Line
ZD81
ZD51
ZD82
ZD83
ZD84
ZD85
D81
R56
R57
GND Line
1
2
8
7
PWDN
+5V Line
GND
R87
R86
R83
R84
+
-7
8
4
6
5
PC1
Q31
R20
Figure 2-26 +35 VLine Overload Detection Circuit
FX-2170 ServiceManual Operating Principles
Rev.A 2-19