Epson SQ-B50/2550 Technical Manual page 128

REV.-A
Constant voltage control:
The constant voltage circuit is shown in Figure 2-69. EA 1 of 494 functions for constant voltage control.
The reference voltage (Vref) is supplied to the reverse terminal of EA 1. The constant voltage circuit of
the shunt regulator L5431 is a constant power supply for setting Vref voltage. The output voltage is
maintained at
+
3VDC by R51 and R50 settings. Ink viscosity will vary with temperature, so ink injection
will be difficult at high viscosity levels.
Therefore, the head drive voltage changes according to the ink temperature detected by the temperature
resistor to ensure that the ink is injected at a constant rate.
The value of Vref changes proportionally with the fluctuation resistance of the temperature sensor. The
Vref fluctuation range is set by the adjustment of the variable resistor VR 1. Figure 2-70 shows the
relationship between ink temperature and drive voltage.
R 41
549
VR1
500
R37
2.43K
R36 4.64K
Vh
R80 365K
GH
E A I
Ink
Tempera t ure
Sensor
(Thermister)
GH
Su ppl Y
1 - - - - - - ,
I +24
t
(3 V)
I
r + - - - - - - ,
I
I
I I
I I
I
I
I I
I I
I
L5
I
I
R51 431 :
I I
: (2D)1
I
R50
I
I I
I
t
!
I
I I
I I
L __
GH __
~
Constant Power
Figure 2-70. Constant Voltage Control Circuit
( V )
1
~~gt
o
::;: 121
~
116
I'D
100
93
5 25
Temperature ..
Figure 2-71. Relationship Between Ink Temperature and Drive Voltage
2-60