Epson FX-2170 Service Manual page 68

FX-2170 Service Manual
3. +35 V Constant Voltage Control Circuit
The +35 V constant voltage control circuit is illustrated below.
Q1
C15
R20 R21
Q2
R19
Figure 2-25 +35 V Line Constant Voltage Control Circuit
The constant voltage control circuit operates to keep the 35 V line at 35 V
ZD51 and ZD85 becomes 32.7 V
FET Q1 shuts off. When the voltage between ZD51 and ZD85 becomes less than 32.7
off, and then Q2 also turns off. Consequently, switching FET Q1 operates again. Repeating the above
operation keeps the +35 V line at 35 V
4. +35V Line Overload Detection Circuit
The +35 V line voltage drop protection circuit is shown in the figure below.
PC1
8 1
Q31
7 2
Figure 2-26 +35 V Line Overload Detection Circuit
When the +35 V line is overloaded, it means that constant voltage control is not being maintained. In this
condition, the forward current of PC1 drops to 0 A. Consequently, voltage Vf between PC1 and D81 also
drops. On this circuit, when the Vf voltage drops below 1.3 V (+35 V line: 33.1 V), IC528 detects the
overload and outputs the PWDN signal (+5 V: HIGH active) to port 20 of the CPU. When the CPU receives
this PWDN signal, printing stops. When the +35 V line becomes normal again, the voltage between PC1 and
D81 also becomes normal. When the Vf voltage goes above 1.6 V (+35 V line: 33.4 V), the PWDN signal is
removed.
Rev.A
C13 R11
R15
Q3
R16
R13
R14
+
C12
IC1
8
7
2.75 %, PC1 turns on, and then Q2 also turns on. Consequently, switching
6%.
ZD51
ZD81
ZD82
ZD83
ZD84
ZD85
R56
D81
R57
11
10+
9+
R56
D81
1
R57
2
6 %. When the voltage between
+35V Line
GND Line
R86
R83
8
5 +
R20
7
6
-
4
R84
Operating Principles
+35V Line
ZD51
ZD81
ZD82
ZD83
ZD84
ZD85
GND Line
2.75 V, PC1 turns
+5V Line
R87
PWDN
GND
2-19