Filament power supply for static vacuum fluorescent display
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United States of America Patent
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Feb 25, 1997
Grant Date -
N/A
app pub date -
Oct 2, 1995
filing date -
Oct 2, 1995
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A DC power supply 44 for providing a desired filament voltage to a static filament in a vacuum fluorescent display 16 includes a voltage regulator 46 with an input and an output. The input couples to a source of ignition voltage 10 while the output couples to the base of a transistor 50. A first dropping resistor 52 connects between the source of ignition voltage 10 and the collector of the transistor 50. A second dropping resistor 54 connects between the emitter of the transistor 50 and the filament 20 of the VF display 16. Accordingly, a first current path to the filament 20 is defined through the first dropping resistor 52, the collector-emitter junction of the transistor 50, and the second dropping resistor 54. A second current path to the filament 20 is defined through the voltage regulator 46, the base-emitter junction of the transistor 50, and the second dropping resistor 54. In operation, therefore, filament current flows through the first current path when the source of ignition voltage 10 is operating in an upper portion of its range dissipating a significant amount of power across the first dropping resistor 52. Alternatively, filament current flows through the second current path when the source of ignition voltage 10 is operating in a lower portion of its voltage fluctuation range.
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