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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
Document File: 2 page(s) / 97K

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.

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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.

Existing problems in triac illumination control circuits are expensive and inefficient. Control of the turn-on voltage waveform is difficult and expensive to implement. Accuracy of the desired lamp voltage is difficult to achieve. Use of electrical hardware based control circuits to produce the controlling feedback increases cost, complexity, and reduces reliability and flexibility.

It is proposed to control the illumination lamp voltage using a power-Mosfet driver circuit. Circuitry also senses the current and voltage of the AC power input to the M...