Browse Prior Art Database

Original Publication Date: 1987-Apr-30
Included in the Prior Art Database: 2004-Apr-04

Publishing Venue

Xerox Disclosure Journal


The regulation of self-biasing developer housings in electrophotographic imaging devices utilizing conductive magnetic brush development has been accomplished through the use of diodes, particularly Zener diodes which are reverse biased in series with the developer housing supply voltage. Two benefits for using this approach are the enablement of copy lighter and copy darker modes and the establishment of boundries for the floating range. A contingency of this control circuit is that the maximum voltage to which the housing will float is equal to the bias source voltage. Since the Zener diode voltage is additive to the required bias voltage, a higher than normal source voltage must be employed. This implies that adjustable voltage sources ar? required to incorporate this concept in a given xerographic imaging device. Since the source voltage may exceed 500 volts for copy lighter, the large voltage may pose design problems. Moreover, the necessity for adjustable source voltages hinders the use of floating bias in many copiers. These limitations may be addressed by the application of a Zener diode control employing both forward and reverse bias Zener diodes in series with the bias source voltage. This means that the source voltage acts as a center line about which the floating range can be established. The range above and the range below the center line are independently established by the choice of Zener