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POWER MOSFET CONTROL OF ILLUMINATION LAMP

IP.com Disclosure Number: IPCOM000025865D
Original Publication Date: 1988-Aug-31
Included in the Prior Art Database: 2004-Apr-04

Publishing Venue

Xerox Disclosure Journal

Abstract

In copiers and scanners, it is necessary to control the amount of light produced by the lamp which illuminates the original document. This is often done by phase controlling the AC line voltage applied to the illumination lamp using a triac and some feedback method to maintain the proper lamp voltage and light output. The feedback method is often solely implemented using electrical hardware. Use of a triac usually requires that an inductor be added to prevent the turn-on voltage rise time from being too fast, which generates electrical noise and failure to meet the requirements of regulatory agencies' radiated and conductive emissions limits. The inductor required can be large and expensive. Also, triacs require special gating circuitry owing to their more difficult input gating requirements. Precise control of the lamp voltage is more difficult using triacs, as the variabilities in the triac gating can lead to errors in the lamp voltage control.