vacuum fluorescent display(VFD); A VFD is built up
of several vacuum fluorecent cells. Each cell is
built in a similar fashion to
triode vacuum tubes; It
consists of an
anode, a
grid and several
cathode filaments.
The anode is given a
layer of
phosphors.
phosphor coated
anode
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grid
This
assembly is put inside a glass
container, the air is
pumped out, and the container is sealed.
To operate the cell, the anode is given a
potential difference to the cathode
of between 150V and 200V(and the
filament is given a glow
current).
When the grid is energized, it creates
an electron flow between the cathode and the anode. This
flow exites the phosphors and they emit light. By
adjusting
the voltage on the grid, the
intencity of the light can be
changed.
By arranging several cells in a
7-segment or a
matrix
pattern a display can be created. The VFD's usualy have a green
or blueish glow. They have a medium to good
contrast, but
has been replaced by
LCDs in most
applications, since
the VFD has a higher power
consumption.