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Custom VFD Glass Design Guidance
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1. VFD Operation |
The VFD is composed
of three basic electrodes; the Cathode (Filaments), Anodes
(Phosphor) and Grids under a high vacuum condition in a glass
envelope.
The Cathode consists of fine tungsten wires which are coated
by alkaline earth metal oxides which emit electrons.
The Grids
are a thin metal mesh which control and diffuse 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, which upon collision with the Anode excites the
phosphor to emit light. The desired illuminated patterns can be achieved
by controlling the positive or negative potentials on each Grid and Anode.
This voltage can be as low as 10VDC. |
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|
Fig.1 Basic VFD Structure |
1. |
Glass Substrate
(Anode Plate) |
10. |
Getter |
| 2. |
Conductive
Layer |
11. |
Face Glass (Cover
Glass) |
| 3. |
Anode
(Base) |
12. |
Spacer
Glass |
| 4. |
Insulation
Layer |
13. |
Evacuation
Tube |
| 5. |
Phosphor (Display
Pattern) |
14. |
NESA (or ITO)
coating |
| 6. |
Conductive
Paste |
15. |
Lead
Pin |
| 7. |
Grid Mesh |
16. |
Mold
Resin |
| 8. |
Conductive Frit
Glass |
17. |
Solder |
| 9. |
Filament
(cathode) |
18. |
Frit
Glass |
2. VFD Construction |
|
Itron VFD has several methods of construction. The basic model is that of
the frame type construction.
The other variants are specific to the
product type and are described in more detail in the relevant
application notes associated with CIG (Chip in Glass Driver), Active
Matrix and Rib Grid
The Grid Rim,
Filament Support and Lead Pins are provided on a single metal frame. The
ends of the Grid Rim are extended to the outside of the envelope, and are
formed as lead pins for Grid. The Anode leads are extended into the
envelope to connect with the pads which are placed on the glass substrate.
Both ends of the filament are welded to the Filament Support and Anchor
with the appropriate tension.
The Frame is assembled with the Face
Glass and Glass Substrate (Anode Plate). The Lead Pins are tinned and
formed into a suitable shape for PC Board assembly.
FRAME-Types require
press formed metal dies for construction. They offer good production yield
and high reliability against various environmental conditions.
A hybrid of this construction
mounts the grids directly on the glass substrate which allows complex grid
patterns. |
Fig. 2 Frame Type Construction |
3. Package Size, Display Area and Viewing Angle Relationship |
Certain mechanical constraints imposed by the drive conditions, construction and materials need understanding before finalizing your initial ideas.
The preferred combinations of package width (W), display area and viewing angle are referred to in Table 1.
After the package width is selected, standard packages can be selected from Table 2.
The length of the display area can be calculated as: P1=L-2xS
The values may vary depending on the package length or construction of the VFD. Please consult us for details.
Full custom packages are possible but it is generally more economical to use standard packages where possible.
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|
Table 1 Package Size
and Display Area (mm)
|
Package
(W)idth |
Display
Area
Width(P2) |
Side
Space(S) |
Viewing
Angle |
Fig.3 Package
Dimensions
Fig.4 Viewing
Angle |
|
| TYP |
MAX |
MIN |
TYP |
TYP |
| 20.5 |
8.0 |
9.0 |
12.0 |
14.0 |
45deg. |
| 25.0 |
12.5 |
13.5 |
12.0 |
14.0 |
49deg. |
| 29.0 |
15.0 |
16.5 |
12.0 |
14.0 |
43deg. |
| 33.5 |
19.5 |
21.0 |
12.0 |
14.0 |
43deg. |
| 40.0 |
26.0 |
27.5 |
12.0 |
14.0 |
43deg. |
| 50.0 |
33.0 |
35.0 |
14.0 |
16.0 |
43deg. |
| 60.0 |
42.0 |
44.0 |
14.0 |
16.0 |
43deg. |
| 70.0 |
56.0 |
58.0 |
14.0 |
16.0 |
40deg. |
Table 2 Standard Package Size (mm) |
|
Package
Length (L) |
| 50 |
60 |
75 |
100 |
115 |
150 |
175 |
205 |
220 |
250 |
Package
Width
(W) |
20.5 |
Y |
Y |
Y |
Y |
Y |
Y |
|
|
|
|
| 25.0 |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
|
|
| 29.0 |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
| 33.5 |
|
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
| 40.0 |
|
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
| 50.0 |
|
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
| 60.0 |
|
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
Y |
The table shows the standard
packages size, suitable and efficient for the automated assembly
process.
Since package sizes other than from the above table are
available, please contact us. |
4. Position and Dimension of Evacuation Tube |
The standard VFD
has an evacuation tube which is sealed once the vacuum is established.
It's location can be varied to suit the space constraints of the
design. An rear mounted metal 'tipless' seal can be utilised at extra
cost where space does not permit a tube to be
used.
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|
Table 3 Evacuation Tube
Position and Dimension (mm) |
|
Position |
Dimension |
 |
| Fig.5 Evacuation Tube
Position |
|
| Standard |
T2
or
T5 |
D |
F |
H(STD) |
| 2.8 |
6.0MAX |
4.0 |
| 3.0 |
8.0MAX |
4.1 |
| 3.8 |
10.0MAX |
4.5 |
| 5.0 |
15.0MAX |
6.0 |
| Custom |
T1,T3 or
T4 |
| D: Tube
Diameter F: Tube
Length H: Dimension
from the center of the tube to the substrate
edge. |
|
5. Pattern Design Rules |
The
standard printed phosphor and grid structure dimensions are limited by
various technology constraints.
Please consult the application note on
fine pattern Rib Grid and Active Matrix VFDs for details of alternate
strategies.
|
|
Minimum Width of Each
Segment. |
0.18mm
MIN for Standard Green
0.20mm MIN for other colors |
|
|
| Minimum Gap
between Each Segment. |
|
| Same
color segments placed on the same anode base. |
 |
| Different color segments placed on the same anode
base. |
 |
|
Same color
segments placed on the separate anode base. |
  |
|
Different color
segments placed on the separate anode base. |
 |
|
|
| Luminous
Uniformity |
| Lighting up large
areas of the display or flashing certain segments may decrease the
luminous uniformity of the display. Restrictions on minimum distance
between anodes as follows |
|
Different anodes
close together |
 |
|
Line formed anode
and another anode close together |
 |
|
|
| Grid
Separation |
|
|
|
|
|
Standard Grid
Mesh Separation |
Grid Mesh
Separation in Hybrid Construction |
|
Please consult us
for the size
of the overlapped area. |
This figure may
vary based
on the
pattern. |
6. Package Thickness and Standard Dimensions of Lead Pins |
| Table 4 relates package width
to package thickness and options for lead pin construction. The standard
lead pitches are 2.54mm and 2.0mm. If you need any different lead lengths,
please consult us. |
|
Table 4 Standard Lead Sizes
for Frame Type Construction (mm) |
Package
Width(W) |
Package
Thickness(T) |
Straight
Leads |
Right Angle
Leads |
 |
| Fig.6 Standard Lead
Pin |
|
| P |
Q |
P |
Q |
R |
| 20.5 |
6.2, 6.7 |
8.0 |
4.0 |
9.0 |
5.0 |
2.0 |
| 25.0 |
6.2, 6.7, 8.0 |
| 29.0 |
7.2, 8.0 |
| 33.5 |
8.0 |
| 40.0 |
8.0 |
| 10.0 |
9.0 |
5.0 |
| 50.0 |
10.0, 11.2 |
| 60.0 |
10.0 |
| 13.2 |
11.0 |
7.0 |
2.5 |
| 75.0 |
13.2 |
|
Table 5 shows the options for welded wire lead assembly where 0.5mm diameter wire pins are welded to frame leads when longer pin length is needed. |
|
Table 5 Standard Lead Sizes of Welded Wire Leads(unit: mm) |
Package
Width(W) |
Package
Thickness(T) |
Straight
Leads |
Right Angle
Leads |
 |
| Fig.7 Welded Wire Lead
Pin |
|
| P |
Q |
P |
Q |
R |
| 20.5 |
6.2 |
35.0MAX
12.0MIN |
7.0 |
28.0MAX
6.5MIN |
3.2 |
2.5 |
| 6.7 |
2.7 |
| 25.0 |
6.2 |
3.2 |
| 7.2 |
2.7 |
| 8.0 |
| 29.0 |
7.2 |
| 8.0 |
| 33.5 |
8.0 |
| 40.0 |
8.0 |
| 10.0 |
1.7 |
| 50.0 |
10.0 |
| 11.2 |
25.0MAX
7.0MIN |
0.7 |
3.5 |
| 60.0 |
10.0 |
| 13.2 |
0MAX |
| 75.0 |
13.2 |
|
7. Drive Scheme and Power Supply |
| Noritake Itron VFD are
available with or without integrated Chip In Glass drive circuits. If the
CPU controlling the display does not provide VFD driver outputs, we
recommend selecting a CIG drive scheme when the number of grid and
anode lead pins exceeds 40. The CIG driver allows direct static drive
at 12VDC for up to 144 segments without the need to multiplex the display
and provides a direct micro-controller clock serial interface. Please
consult the application notes on VFD Technology and Chip In Glass VFD for
further details.
The Cathode (Filaments) are normally driven by an
AC supply of 2Vac to 9Vac which can be generated by a transformer or
transistor bridge circuit to provide a current of 22mA to 200mA depending
on display size. The anode and grid voltage require a supply of 12V for
static drive and 24V to 70V with a current capability of 10 to 60mA for
multiplex drive schemes dependent upon the number of grids scanned. Please
advise the voltages that are available in your
system. |
8. Selecting Phosphor Colours |
| The standard phosphor colour
is green which can be complemented by a range of other phosphor colours
shown in Table 6 to provide a bright multi-colour display. The names of
the phosphors were changed in January 2000.
If by definition, Green
(Blue Green) is rated 100%, each of the colors when driven under the same
conditions would be rated as shown in the brightness ratio of Table 6.
Although there are different brightness characteristics between phosphors,
this is not always readily apparent because a sensitivity of human eyes to
brightness varies with color wavelength. Therefore, legibility may not be
affected. In a multicolor display specific brightness balance can be
achieved by controlling voltages and/or duty factor of each
color.
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|
Table 6 VFD
Phosphor Colour Chart |
| Name of
Color |
CIE color
coordinate (TYP) |
Brightness
Ratio |
| New Name |
Previous
Name |
X |
Y |
% |
| Blue (B) |
Blue |
0.14 |
0.18 |
15 |
| Light Blue
(lt.B) |
Neo Blue |
0.18 |
0.19 |
10 |
| Light Greenish
Blue-N (lt.G.B-N) |
Sky
Blue(Blue) |
0.18 |
0.27 |
20 |
| Bluish Green
(B.G) |
Sky Blue
2 |
0.20 |
0.40 |
45 |
| Green (G) |
Blue
Green |
0.24 |
0.41 |
100 |
| Vivid Green
(vv.G) |
Emerald
Green |
0.10 |
0.73 |
20 |
| Yellowish Green
(Ysh.G) |
Neo Green |
0.28 |
0.62 |
20 |
| Yellow Green
(Y.G) |
Lemon |
0.38 |
0.57 |
40 |
| Greenish Yellow
(Gsh.Y) |
Yellow |
0.47 |
0.51 |
30 |
| Yellowish Orange
(Ysh.O) |
Amber |
0.53 |
0.47 |
30 |
| Orange
(O) |
Mandarin |
0.60 |
0.40 |
20 |
| Reddish Orange
(Rsh.O) |
Red |
0.64 |
0.36 |
10 |
|
Note: These figures are
for reference only, because the brightness depends on its driving
conditions.
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|
Fig 8 CIE
Chromatocity Diagram
|
Fig 9 Spectrum
of Colour Phosphor Material
Note: The peak
wave length of each color may vary and the figures in the above are for
reference only.
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9. Environmental Considerations |
The operating temperature range for standard VFD with frame construction is -40C to +85C.
Please submit the expected storage temperature and humidity range and vibration data. |
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