Epson STYLUS Scan 2000 Service Manual page 51

EPSON Stylus Scan 2000
SECONDARY SIDE
+42V +5V
+3.3V
+3.3V regulator
IC51
+5V regulator
+42VDC line over
voltage limitation
ZD51,ZD81-86
+42V line
constant control
+12V
regulator
IC53
+12V line over
voltage limitation
Smoothing
C51,C52
circuit
C56,Q82,
D51
Q83
Transformer (T1)
C11
Q1
Smoothing
switch-
circuit
Filter circuit
Fuse
F1 L1, R1,
C1-4
AC input
Figure 2-21. B101 PSB/PSE Board Block Diagram
Operating Principles
Power signal
from MAIN
board/power
switch
+5V line over
voltage limitation
ZD53
ZD52,87
+12V
ZD55
Power drop
delay circuit
PC1
Photo coupler
Main
Feedback
circuit
Full wave
rectifier circuit
DB1
PRIMARY SIDE
Electrical Circuit Operating Principles
1. As long as the AC plug 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.
Q2,Q3,Q
31,IC1
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.
Revision A
51