Power Supply Circuit Operation - Epson FX-2170 Service Manual

Operating Principles

2.2.2 Power Supply Circuit Operation

The power supply circuit is composed of an RCC (ringing choke converter) system and the power switch
circuit in the secondary circuitry. The power supply circuit has several protection and control circuits. This
section describes these circuits.
1. Power Switch Circuit
The power switch circuit is in the secondary circuitry. It is shown in the illustration below.
8
7
Q 3 1
When printer power is off, the PSC line is connected to a ground line and the current is loaded from
C55 to PC1. Consequently, Q32 and Q31 are turned on, and the switching FET is shut off.
(2) +35 V/+5 VDC Line Over Voltage Protection Circuit
This circuit is shown below.
PC1
6
5
Q31
FET
Figure 2-24 Over Voltage Protection Circuit
The +35 VDC over voltage protection circuit operates when voltage exceeds 42.42 V between ZD52 and
ZD87 and shuts off the switching FET (Q1: K2126 or K2130). The +5 VDC over voltage protection circuit
operates when voltage exceeds 7.5 V between ZD53, and shuts off the switching FET (Q1: K2126 or
K2130). When either of these protection circuits operate, the protection cannot be removed without turning
power off and on again.
2-18
R 9 1
D 5 2
C 5 5
3
6
5
4
P C 1
Figure 2-23 Power Switch Circuit
ZD86
3 R89
4
+35V Line
D 8 5
D 8 4
R 6 8
PSC line
R 6 9
Operation SW
O F F
(Power SW)
C82
Q81
R90
D82
Q55
GND
FX-2170 Service Manual
+35V Line
ZD52
ZD87
ZD53
+5V Line
Rev.A