Service manual

Principles of Operation
A/D Converter Circuit
Figure 2-51 shows the A/D converter circuit. The converter has the following
functions:
l
Monitors the +24 V line to determine the drive pulse width for the printhead.
l
Monitors the temperature (the resistance) of the printhead.
l
Reads the initial DIP switch settings.
l
Reads the bidirectional adjustment setting.
Shunt regulator TL431CLPB and resistors R37 and R55 regulate reference voltage
Vref as follows:
Vref = g (R55+R37) = 4.5 V
Note: The shunt regulator’s reference voltage is 2.5 V.
Using this value as a reference, AN0 monitors the +24 V line, AN1 monitors the
printhead temperature, and AN2 through AN7 read the DIP switch and
bidirectional adjustment settings.
2-52
LQ-200/AP3000