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DYNAMIC CONTROL OF MOSFET SWITCHED HEATED FILAMENT

IP.com Disclosure Number: IPCOM000026532D
Original Publication Date: 1992-Aug-31
Included in the Prior Art Database: 2004-Apr-06
Document File: 4 page(s) / 141K

Publishing Venue

Xerox Disclosure Journal

Abstract

The present invention is an improvement in the control algorithm used to regulate the switched power supplied to the lamp or filament, in order to maintain the illumination at a specific level, independent of variations in line voltage. As illustrated by the figures, the full-wave, rectified input voltage of Figure 1, is switched at an appropriate time, or conduction angle (a), to achieve the output waveform of Figure 2. The lower axis of the figures represents the phase of the DC power, where 180 degrees equals approximately 8.33 milliseconds for 60 Hz power. In one embodiment, the illumination source may be a tungsten filament lamp, where the illumination intensity is a function of the filament temperature. Moreover, the heating is controlled by the switched, full-wave rectified DC voltage of Figure 2. By switching the power supplied to the lamp off at a predetermined time, a, the amount of energy supplied to the filament is regulated, thereby controlling the filament temperature.

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Page 1 of 4

XEROX DISCLOSURE JOURNAL

DYNAMIC CONTROL OF MOSFET SWITCHED HEATED FILAMENT US. C1.355/228 David J. Breed
John M. Magde, Jr.

Proposed Classification

Int. C1. G03G 15/04

LAMP CONTROL INPUT

90 180 270 360 450 540

0

DEGREES

FIG. 1

LAMP CONTROL OUTPUT

DEGREES

FIG. 2

XEROX DISCLOSURE JOURNAL - Vol. 17, No. 4 July/August 1992 241

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Page 2 of 4

DYNAMIC CONTROL OF MOSFET SWITCHED HEATED F I LAME NT( C ont 'd)

As described in the Xerox Disclosure Journal, Vol. 13, No. 4 (July/August 19881, a power mosfet may be used to control an illumination lamp in a copier or scanner. The present invention is an improvement in the control algorithm used to regulate the switched power supplied to the lamp or filament, in order to maintain the illumination at a specific level, independent of variations in line voltage. As illustrated by the figures, the full-wave, rectified input voltage of Figure 1, is switched at an appropriate time, or conduction angle (a), to achieve the output waveform of Figure 2. The lower axis of the figures represents the phase of the DC power, where 180 degrees equals approximately 8.33 milliseconds for 60 Hz power. In one embodiment, the illumination source may be a tungsten filament lamp, where the illumination intensity is a function of the filament temperature. Moreover, the heating is controlled by the switched, full-wave rectified DC voltage of Figure 2. By switching the power supplied to the lamp off at a predetermined time, a, the amount of energy supplied to the filament is regulated, thereby controlling the filament temperature.

The desired lamp temperature is determined using calibration techniques, and the dynamic control algorithm is then used to maintain the desired temperature, or illumination level. Control is accomplished by holding the root mean square current (Irms) at a constant level. However, the present embodiment, preferably a Xerox 5028@ copier, only has electrical components suficient to monitor the line voltage, rather than the current through the lamp. Because the lamp filament reaches an equilibrium temperature where the lamp resistance is constant, the root mean square voltage, Vrms, is controlled to achieve the desired control of the fi...