Epson Stylus Color 440 Service Manual

EPSON Stylus COLOR 440, 640, and 740 Chapter 2 Operating Principles
50
volta
g
e, the power suppl
y
’s cost is reduced.
(
Althou
g
h a small
transformer is still used, it’s relativel
y
inexpensive compared with the
lar
g
e, heav
y
transformer that would otherwise be needed.
)
The RCC switchin
g
circuit works b
y
alternatel
y
ener
g
izin
g
and de-
ener
g
izin
g
the transformer. Oscillation be
g
ins when the volta
g
e at the
g
ate of Q1 rises throu
g
h kick-start resistor R18. Current passin
g
throu
g
h Q1 enters transformer T1, ener
g
izin
g
its primar
y
coils. Since
diode D51 prevents current from flowin
g
throu
g
h the transformer’s
secondar
y
coils, the transformer is forced to store the ener
gy
as a
ma
g
netic field.
After startup, Q1 is held b
y
volta
g
e supplied b
y
the transformer. This
volta
g
e is switched on and off b
y
IC1, a pro
g
rammable uni
j
unction
transistor
(
PUT
)
. As the transformer becomes ma
g
neticall
y
saturated,
its output volta
g
e drops below the PUT’s holdin
g
threshold, and the
PUT shuts off. This deprives Q1 of volta
g
e, causin
g
it to shut off and
allowin
g
the transformer to release its stored ener
gy
. As the ma
g
netic
field collapses, current be
g
ins flowin
g
throu
g
h the transformer’s
secondar
y
coils.
(
Since the current’s direction is reversed durin
g
dischar
g
e, diode D51 no lon
g
er blocks its flow.
)
When the transformer
has full
y
de-ener
g
ized, the c
y
cle repeats. The resultin
g
pulsed output
contains less ener
gy
than the ori
g
inal input, since the unwanted ener
gy
has been chopped out, and can now be used for the final stepped-down
volta
g
e. To smooth the waveform, capacitor C51 filters the output,
which is then re
g
ulated at 42 volts b
y
a stack of seven 6-volt zener
diodes.
As discussed above, the power suppl
y
contains a built-in dela
y
that
enables the printer to remain on lon
g
enou
g
h to complete its power-
down operations. When
y
ou turn on the printer b
y
pressin
g
the power
switch on the front control panel, the power control si
g
nal
(
PSC
)
from
the main board ener
g
izes transistor Q84, which acts as a rela
y
and
turns on the power suppl
y
. At the same time, the PSC char
g
es
capacitor C84. As a result, even when
y
ou shut the printer off, the
capacitor continues suppl
y
in
g
power to Q84 and keeps the printer on for
at least an additional 30 seconds.
To protect the printer, the power suppl
y
incorporates over-volta
g
e,
under-volta
g
e, and short-circuit protection circuitr
y
. These circuits
contain zener diodes, which monitor the re
g
ulated output volta
g
es. If
the 5-volt suppl
y
exceeds 9 volts, or if the 42-volt suppl
y
exceeds 48
volts, the RCC switchin
g
circuit is immediatel
y
shut off and its output
falls to zero. In addition, a volta
g
e drop protection circuit protects the
printer in case of a short circuit in an
y
component that draws from the
42-volt line. This also works b
y
shuttin
g
off the switchin
g
circuit, which
occurs when output falls below 36 volts. Finall
y
, fuse F1 protects the
power suppl
y
itself, in case of a short circuit in an
y
primar
y
component.
Figure 2-16. PSB, PSE Board Block Diagram
F1
C11
L1,R1-2
C1-C4
DB1
Transformer (T1)
Fuse
Filter Circuit
Bridge
Rectifier
Smoothing
Capacitor
Main Switching
Transistor
Q1
Feedback circuit
Q2,Q3,Q31
Photo-
Coupler
PC1
D51
AC Input
Smoothing
Capacitor
C51
+42VDC Line
Voltage Regulator
ZD81-86,ZD51
Power Drop
Delay Circuit
C84,Q84
+42VDC Line
Over-Voltage
Monitor
ZD52,87
+5V Regulator
IC51
+42 VDC
+5 VDC
+5VDC Line
Over-Voltage
Monitor
PSC
ZD53
+42VDC Line
Under-Voltage
Monitor
ZD90
Feedback circuit

Epson Stylus Color 440 Specifications

General

Brand	Epson
Model	Stylus Color 440
Category	Printer
Language	English