Epson TM-U675 Service Manual page 244

Confidential
The SHEAD 1-9 signal lines (LOW active) are on the left side. These signals are directly driven
by the GA (directly connected to GA [U30]). Signals SHEAD 1-9 are input to the head drive
(QM3, 6, Q12: All NPN Darlington transistors) via the print driver (QM2, 4, 5, 7, Q13: All PNP
transistors). The driver is an NPN Darlington transistor. The driver is internally clamped at Vce
±
= 60V 10V by an internal Zener. The driver performs logical calculation at hgf>1000, providing
adequate flow for one solenoid. To utilize the regenerative current of the head solenoid
effectively, the regenerative current when the GND
channeled to the solenoid. With this printer, the head drive signal is controlled by the GA, and
at the same time, the COMMON (24V power source voltage side) is chopped, enabling efficient
head drive. The chopping circuit is shown below:
HEADCOM1
The HEADCOM1 common drive signal driven by GA (U30) drives the Q7 MOSFET. Since it is
necessary to drive Q7 at high speed (100 KHz or less), a speed-up circuit is added (Q47
periphery, pulls out electric gate load of Q7). The operating principle of the speed-up circuit is
not described here. The relationship of the HEADCOM1 signal and SHEAD signals are shown
below. The chopping cycle of the HEADCOM signal differs, depending on the voltage and
temperature, but is virtually the same as the waveform in the diagram.
Appendix D-56 Product Overview
D47
Q14
Figure D-51
Figure D-52
COMMON is turned off by D6, D7 is
R182
Q47
D48
R37
D6
Solenoid current
S H E A D 1 t o 9
H E A D C O M 1
24VB
ZD1
10K
Q7
D7
Rev.D