Epson Stylus Color 740 Service Manual

EPSON Stylus COLOR 440, 640, and 740 Chapter 2 Operating Principles
49
2.2.1 Power Supply Board
The St
y
lus COLOR 440, 640, and 740 use one of two power suppl
y
boards: the PSB, which accepts 120 volts, or the PSE, which accepts
240 volts. The difference between them lies in their primar
y
circuitr
y
,
which includes the power line filter, the main switchin
g
transistor, and
the transformer. In the PSE, these components are desi
g
ned to
withstand hi
g
her input volta
g
es than in the PSB. Except for these
differences, the two boards are exactl
y
the same.
The power suppl
y
provides filtered output at 5 and 42 VDC. These
volta
g
es power the various printer functions shown in the table below.
Table 2-8. Power Output Applications
Built into the power suppl
y
is a dela
y
circuit, which keeps the printer full
y
powered for about 30 seconds after the printer is turned off.
(
This works
onl
y
when
y
ou turn the power off b
y
pressin
g
the Power switch on the
front control panel; the printer will
not
sta
y
on if
y
ou unplu
g
it.
)
The
dela
y
g
ives the printer time to e
j
ect an
y
paper that ma
y
be in the paper
path and to return the carria
g
e to its home position.
(
The carria
g
e must
return to its home position in order to cap the printhead. If the printhead
remains uncapped, ink dries out and clo
g
s the printhead.
)
Power Supply Operation
When the printer is plu
gg
ed in, electricit
y
is alwa
y
s present in the
primar
y
circuitr
y
of the power suppl
y
. This means that certain
components are alwa
y
s “hot,” includin
g
the power line filter circuit, the
main switchin
g
transistor, and the transformer. Note that the heat sink
on the main swtichin
g
transistor
(
Q1
)
is
not
electricall
y
isolated. Never
touch the primar
y
components of the power suppl
y
with the printer
plu
gg
ed in.
The secondar
y
power suppl
y
circuitr
y
, as well as the rest of the printer’s
electrical components, are electricall
y
isolated from the primar
y
power-
line volta
g
e. Isolation is accomplished b
y
transformer T1 and photo-
coupler PC1.
The power suppl
y
consists of a line filter, a ZC-RCC
(
Zero-Cross
Rin
g
in
g
Choke Converter
)
switchin
g
circuit, and a 5-volt chopper
re
g
ulator IC. See Fi
g
ure 2-16. When AC power enters the printer from
an external power source, the line filter blocks power-line transients
from enterin
g
the printer and prevents radio fre
q
uenc
y
interference
(
hi
g
h-level harmonics
)
g
enerated b
y
the switchin
g
circuit from bein
g
placed back onto the power line. In the PSB board, the primar
y
current
(
at 120 VAC rms
)
then under
g
oes full-wave rectification and is
smoothed to produce 160 VDC.
(
In the PSE board, the 220 VAC input
is over 300 VDC after filterin
g
.
)
This is fed throu
g
h the RCC switchin
g
circuit and a secondar
y
smoothin
g
circuit to produce a stepped-down 42
VDC; feedback ensures stable output. A second, additional output at 5
VDC is produced b
y
a chopper re
g
ulator IC which draws from the 42-
volt suppl
y
.
At the heart of the switchin
g
circuit is a power MOSFET
(
Q1
)
, an
efficient t
y
pe of transistor that dissipates relativel
y
little heat. B
y
usin
g
a
transistorized switchin
g
circuit instead of a transformer to re
g
ulate
Voltage Application
42 VDC CR motor
PF motor
Printhead PZTs
5 VDC Logic circuitry
Control signals
Sensors
Control panel LEDs
Printhead nozzle selector IC

Epson Stylus Color 740 Specifications

General

Brand	Epson
Model	Stylus Color 740
Category	Printer
Language	English