Fig. 2.20 Current Waveform Of Print Head - Epson MX-80 Technical Manual

(a) Head driver
REV. A
The head driver mainly consists of 9 transistors (2S0986). The current waveform of
the print head is shown in Fig. 2.20.
1 - - - - - - - 2 . 1
ms--------l
Approx.
0.4
ms
80
ILS
Approx. 0.7 A
Fig. 2.20 Current Waveform of Print Head
Since a load to be connected to the col/ector of each transistor (2S0986) is a com-
ponent of inductance, the transistor is regulated by a zener diode so that a col/ector
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
Ie
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.
0.5
0.46
ms
Ul
5
:S
-0
'~
OJ
!:!l
:::J 0.4
D-
Ol
C
>
';::
-0
-0
oJ
OJ
I
0.3~--------4-----------------+----------------~-----
24
24-10% 24+ 10%
Voltage Applied to Print Head (VDC)
Fig. 2.21 Applied Voltage vs. Driving Pulse Width
2-20