DYNAMIC CONTROL OF MOSFET SWITCHED HEATED FILAMENT
Original Publication Date: 1992-Aug-31
Included in the Prior Art Database: 2004-Apr-06
Xerox Disclosure Journal
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.