Epson MX-80 Technical Manual page 33

(a) Head driver ^
The head driver mainly consists of 9transistors (2SD986). The current waveform of
the print head is shown in Fig. 2.20.
Approx.
0.4 ms
•2.1 ms-
Approx. 0.7A
80 fis
Fig. 2.20 Current Waveform of Print Head
Since a load to be connected to the collector of each transistor (2SD986) is a com
ponent of inductance, the transistor is regulated by a zener diode so that a collector
breakdown voltage will not occur due to the counterelectromotive force generated
at the time of switching off the transistor. The driver circuit also incorporates an IC
timer to obtain a head driving pulse width corresponding to the voltage fluctuation,
so that a constant output energy is always maintained at the print head solenoid
according to the change in the voltage applied to the print head.
Fig. 2.21 illustrates the relationship between the voltage applied to the print head
and head driving pulse width.
mi
0.5
bet
0.46 ms
(Mt
</)
E
0.41 ms
0 44 ms/
5
OA
0)
1/)
3 0.4
0.37 ms
CD
C
'>
0.39 ms /
hmti
•O
T3
0)
X
0.35 ms /
Ijtti
0.3
1 1 1
1 I
1
aw)
21 /
r 22 23 24 25 26 / 2/
24-100/. / 24-1-10%
Voltage Applied to Print Head (VDC)
i m
Fig. 2.21
Applied Voltage vs. Driving Pulse Width
m t
REV. A
2-20
1