Epson LX-810 Technical Manual

REV.-A
Over-Current Protection Circuit
Error amplifier
EA2, in the KPC494, detects over-current caused either by abnormal operation, or by
abnormality
in the 24V line at the time of power up. Current-detecting resistor R2 is set at the EA2’s
positive terminal (pin 16), and the current, converted to a voltage value, is monitored. The negative
terminal of the
EA2 is connected to the dividing circuit for the standard voltage (+ 5V) and the 24V
output.
Immediately after power enters the circuit, and until the time that 24V output begins, the voltage at
the negative terminal of
EA2 is about 19.2 mV:
Vxl = (RI 1 X 5V)/(R7+R 1 1).
After 24V output begins, the voltage at the terminal is about 0.31 V:
VX2 = (R1 1 X 24 V)/(Rl 1 +Rl 2+R 16).
;.., .,
4
In order for the positive terminal of EA2 to generate the same conditions, the lx current, immediately
—
after power up, is about 192 mA (11 = 19.2mV/R 1 ). During operation, the lx current is about 3.1A
(12=0.3 I/RI).
Accordingly, this circuit is furnished so that, in the event of the problems listed
below, it will halt 24V
switching, in order to prevent the propagation of damage.
When, at the time of power up, abnormality in Q
1 or elsewhere causes excessive current leak to the
24V output line.
When excessive current leak occurs during operation due to abnormality in the motor or the dot head.
Vref
+
R12 R16
4.75KI 9.6K
~g R7 +24V
;“ 82K
line
P’
,\ .-.,
?75’
Figure 2-18, Over-Current Protection Circuit
2-16

Epson LX-810 Specifications

General

Print Method	Impact dot matrix
Number of Pins	9
Character Sets	96 characters (USASCII)
Line Spacing	1/6 inch
Paper Path	Rear
Interface	Centronics parallel
Noise Level	55 dB (A)