Epson FX-2170 Service Manual page 69

Operating Principles
5. +35 V Line Over Current Protection Circuit
The +35 V line over current control circuit is illustrated below.
6
Q31
5
Figure 2-27 +35 V Line Over Current Protection Circuit
When the +35 V line becomes less than 27 V, Q82 and Q54 turn on, and PC1 turns on. Consequently, Q32
and Q31 turn off, and then switching FET Q1 shuts off. When the protection circuit operates, this protection
can only be removed by turning the power off and on again.
6. +5 V Line Over Current Protect Circuit
+5 V line over current control circuit is shown below.
+35V Line
IC51
TL494CN
-
+
Figure 2-28 +5 V Line Over Current Protection Circuit
Port 2 of IC51 (TL494CN) monitors the +5 V line, and this protection circuit operates when the +5 V line
goes below 4.75 V. When this circuit operates, port 8 signal output of the PWM pulse stops, and Q51 stops its
switching operation. Consequently, the +5 V line stops generating.
2-20
D85
3
Q54
4
R68
L51
Q51
R61
R51
D51
8
R67
2
-
+
1
R54
R70
Q53
R71
C57
R74
R75
Q82
R53
R88
R64
R65
FX-2170 Service Manual
+35V Line
R72
R73
GND
PSC
+5v Line
GND
Rev.A