Vacuum Fluorescent Display (VFD)

Description

How to power a vacuum fluorescent display (VFD)
The vacuum fluorescent display has 3 different components:

  • Grids
  • Segments (anodes)
  • Cathode heater (cathode)

It has a directly heated cathode, so the cathode heater is also the cathode.
Voltage across cathode heater should be about 3V.
It should not glow visibly red.
Anode voltage should be anywhere between 10V and 50V.
If the VFD glows too brightly, the phosphor's life will be shortened, and it will become duller.

Each VFD usually contains multiple digits.
Each digit has a corresponding grid, which seperates the cathode from the digits' segments.
The segments of each digit are common with their corresponding segments on all the other identical digits.

For example, a VFD with 4 seven segment digits will contain 7 segment connections, 4 grid connections, and 2 for the cathode heater.

0V of the anode supply should connect to either side of the cathode,

+V of the anode supply should connect to the segment(s) that are to be activated, and the grid which corresponds to the digit whose segments you want to activate.

Picture

VFD.jpg

Diagram

Diagram.png

Internal connections to segments are omitted from diagram for clarity

In the diagram above, the connections labelled 1,2,3,4 are the grids.
And the connections labelled A,B,C,D,E,F,G are the segments (anodes).
The connections labelled "Heater (cathode)" are either side of the cathode heater.

Examples

To display an 8 on the second digit,
A voltage of 3V would be applied between the two Heater connections
A voltage of +12V relative to either Heater connection would be applied to A,B,C,D,E,F,G and 2.

To display a 1 on the fourth digit,
A voltage of 3V would be applied between the two Heater connections
A voltage of +12V relative to either Heater connection would be applied to B,C and 4.

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