Epson Stylus Scan 2000, Service Manual

Page: 50 / 264

EPSON Stylus Scan 2000 Revision A
Operating Principles Electrical Circuit Operating Principles 49
Figure 2-23. B101 PSB/PSE Board Block Diagram
1. As long as the AC adapter is plugged into a power source, voltage flows through the
primary side (bottom in figure above) of the power supply board.
2. The fuse prevents damage to the power supply board in case the current is too strong.
3. The filter circuit acts to filter incoming electrical noise and to smoothen the electrical
current.
4. The full wave rectifier circuit converts AC to DC.
5. The smoothing circuit stabilizes out the DC wave.
6. The main switching circuit controls the flow of current to the transformer (hence to the
entire secondary side). The main switching circuit, transformer, and feedback circuit
work in combination like the heart, lungs, and brain (respectively) of the human body.
The main switching circuit is the variable-flow generator like the heart, the transformer
convert the power to a usable form like lungs adding oxygen to blood, and the
feedback circuit controls the flow like the brain controlling the heartbeat/pulse.
7. The transformer receives approximate 100V or 220V DC (depending on the model)
current and steps the current down before sending it out to the secondary side.
8. The current is stabilized as it goes through another smoothing circuit.
9. The +12V, +5V, and +3.3V regulators control the flow of current so that only the rated
voltage flows through each regulator.
10. The +42V, +12V, and +5V line over-voltage limitation protectors monitor their
individual lines for any voltage over the rated amount. If over-current is detected, a
signal is sent to the photo coupler to decrease current.
11. The +42V line constant control is similar to a regulator in that it is always working, but
instead of fixing the current it reports over-current to the photo coupler.
12. The photo coupler communicates over-current problems to the feedback circuit by
means of a photo emitter. A photo emitter is used to make sure that currents between
the primary side (AC as well as DC) and secondary side (DC only) do not mix and
short the board.
13. The feedback circuit 1) receives over-current information from the photo coupler by
means of a photo receiver 2) monitors the transformer for over-current and 3) receives
power-supply information/commands from the MAIN board and power switch. The
feedback circuit slows down the voltage sent from the main switching circuit to the
transformer when necessary.
14. The power-drop delay circuit is a thirty-second timer that makes sure there is enough
time to complete the power-down sequence after power is turned off.
Fuse
Filter circuit
Full wave
rectifier circuit
F1 L1, R1,
C1-4
DB1
Smoothing
circuit
Main switch-
ing circuit
Q1
C11
Q2,Q3,Q
31,IC1
Transformer (T1)
Smoothing
circuit
Power drop
delay circuit
+12V
regulator
+12V line over
voltage limitation
D51
C51,C52
ZD51,ZD81-86
+12V
ZD55
+42V line constant
control
IC53
+42VDC line over
voltage limitation
+5V line over
voltage limitation
Photo coupler
Feedback circuit
PC1
C56,Q82,Q
83
Power signal
from MAIN
board/power
switch
+5V regulator
+5V +42V
IC51
ZD52,87
ZD53
AC input
+3.3V regulator
+3.3V
PRIMARY SIDE
SECONDARY SIDE