Vacuum Fluorescent Displays

Vacuum fluorescent display tubes share more in common with a cathode ray tube than they do with the Nixie tubes they tend to mimic. A VFD tube has a low voltage filament which is energized in a vacuum, causing electrons to 'boil' off. Metal plates covered with a phosphor coating are charged to between 25 and 50 volts, causing electrons leaving the filament to strike the plates and illuminate the phosphor. Later models of VFD also have a control grid, a metal screen that is placed between the digit and the filament. The control grid acts as a valve, allowing the digit to be turned on or off without the need to power down and re-heat the filament.

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