Epson Stylus COLOR 440 Service Manual page 70

EPSON Stylus COLOR 440, 640, and 740
Common Voltage Drive Circuit
The common voltage drive circuit generates the voltage waveform for
driving the PZTs (piezo-electric elements) in the printhead. The gate
array outputs signals to the common drive IC (H8D2813, H8D2889, or
CXA20995 in the Stylus COLOR 440, 640, or 740). The common drive
IC then drives 2 power transistors arranged in a push-pull configuration
(see Figures 2-32 through 2-34 below). The waveform produced by
these transistors is called the "trapezoidal" waveform, because it looks
like an irregularly shaped trapezoid with a small step in the middle. The
trapezoidal waveform can be observed any time the printer is on,
whether something is being printed or not.
Table 2-9. Common Voltage Driver Characteristics
Items
42 volts ± 5%
Drive voltage
Waveform appears after voltage rises above 5 volts.
Final drive element 2SC3746 (PNP)
(power transistors) 2SA1469 (NPN)
Operation during reset Both transistors are off.
Nozzle Selector Drive Circuit
The nozzle selector IC is located in the printhead itself. Data from the
gate array is sent serially to the IC and latched in one-byte units. After
the IC interprets the data, it sends print signals in parallel to the
appropriate PZTs. These signals are synchronized with the trapezoidal
waveform produced by the common voltage driver, and determine
which PZTs get actuated by the common voltage in each cycle.
Figure 2-32, Figure 2-33, and
diagrams for each printer.
Characteristics
Figure 2-34 show printhead driver
Chapter 2
+42
F1
H8D2813(IC6)
2
CHG
XOVM
4
KC1
CTB
ND1
COM
6
ND2
DTB
MD1
MD2
+5
Data
CLK
20
/STB
Vcc
/CLR
1
GND
VRF
VK GND
25
E05B44(IC2)
200
199
SW7
VHCTL
VHCTL
198
SW8
CHG
90
KC1
LP
ND1
99
BIEN
ND2
100
MD1 BHSO
97
MD2
YCMIEN
Data
96
YCMHSO
CLK
93
/STB
ICLK
/CLR 92
BCHCLK
VRF
89
VK /NCHG
TMP95C061(IC1)
20
AN0
Figure 2-32. Head Drive Circuit for Stylus COLOR 440
Operating Principles
22
CN8
VHV
23
VHV
+5
15
VDD
14
GND
12
GND
10
GND
8
GND
6
GND
4
GND
19
COM
20
COM
21
COM
16
GND2
17
GND2
18
GND2
1
BCO
2
CCO
5
LAT
9
SI1
7
SI2
11
CLK
13
NCHG
3
THM
61