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Optoelectronics/Displays??

Vacuum fluorescent display (VFD) reference design for automotive applications

Posted: 12 May 2009 ?? ?Print Version ?Bookmark and Share

Keywords:reference design? VFD display? automotive?

The vacuum fluorescent display (VFD) is composed of three basic electrodesthe cathode filaments, anodes (phosphor) and gridsunder a high-vacuum condition in a glass envelope. The cathode consists of fine tungsten wires, coated by alkaline earth metal oxides that emit electrons. The grids are a thin metal mesh, which controls and diffuses electrons emitted from the cathode. The anodes are conductive electrodes on which the phosphor is printed to indicate characters, icons or symbols. Electrons emitted from the cathode are accelerated with positive potential applied to both grid and anode; upon collision with the anode, the electrons excite the phosphor to emit light. The desired illuminated patterns can be achieved by controlling the positive or negative potentials on each grid and anode. The anode and grid require a DC-regulated voltage to avoid flickering of the display. For driving large VFDs, the cathode requires AC drive to prevent luminance slant, i.e. the difference in brightness from one side of the display to the other. A frequency range of 20kHz to 200kHz is recommended to avoid audible noise and flicker.

This reference design shows a solution for obtaining the drive voltage required for a VFD power supply in automotive applications. The design includes the complete schematic, and presents the BOM, load/line regulation measurements, and test results.

View the PDF document for more information.





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