Printer; Developing Bias Control Circuit - Printronix L5535 Maintenance Manual

Developing Bias Control Circuit

Developing Bias Control Circuit
Drum cleaning occurs when the printer begins to print each page, as well as
during printer initialization when the printer power is turned on.
Circuit action begins when the controller sends the MC board a command to
set the developing bias potential. This command contains a byte of data that
represents the desired developing roller bias voltage. The CPU on the MC
board stores this data byte in the MC board data memory as a target
potential.
When drum cleaning begins, the CPU on the MC board retrieves the target
data byte from the data memory and sends it to the developing bias control
circuit on the MC board.
In the developing bias control circuit, a digital-to-analog (D/A) converter
converts this digital target byte to an analog signal, then an operational
amplifier scales the signal to a range of 0 to +12 volts (DRL CONT), before
sending it to the high-voltage power supply.
As the charged portion of the drum passes the developing roller, the MC
board asserts the developing bias remote ON/OFF (DRL REM) signal to the
high-voltage power supply, and the high voltage power supply sends the bias
voltage to the developing roller. This bias voltage consists of a DC component
(+200 to +600 VDC) and a superimposed 10.5 KHz AC component (variable
between 1000 to 2000 V p-p).
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