| DRIVING METHOD of VFD |
APN201 |
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1. Operating principle of the VFD
The VFD is a kind of triode vacuum tube with three electrodes, which are;
- Cathode Filament(s)
- Control Grids
- Illumination Anodes
The electrons emitted from the cathode filaments are controlled by the grids.
When the grid is supplied with a positive voltage,
it attracts the negative electrons, diffuses them and,
due to their acceleration, they flow through the grid mesh towards the anode
(opposite charges attract).
However, when the grid is supplied with a negative voltage,
it repels the negative electrons and prevents them from reaching the anode
(similar charges repel).
The illuminating anodes are coated with phosphor which emits light when hit by the electrons.
Each anode forms a segment or dot, which collectively form individual characters.
When an anode is supplied with a positive voltage,
it will attract the electrons which have been accelerated through the grid above.
The segment emits light when these electrons impact on the phosphor coating.
Alternatively when anodes are supplied with a negative voltage,
they will repel electrons from their phosphor coating and therefore remain un-illuminated.
By selecting combinations of illuminated segments,
the desired digit or character can be formed.
2. Electrical Characteristics of the VFD
3. Timing Characteristics for Correct Operation
4. Filament Power Supply
5. Filament Bais Voltage (Cut-off Bias)
6. Anode and Grid Power Supply
7. Driver
Since the advent of the new VFD driver IC's which offer shift resistor,
latch and high voltage outputs, interface to the CPU becomes relatively simple.
A CPU chip with high voltage outputs will meet the requirements of the VFD.
Note when using the CPU with VFD drivers,
we recommend that an active pull down output or pull down resistors of 50 to 120k ohm
are used in order to prevent excessive delay time.
Standard Driver ICs (Oct. 1997)
| Manufacturer | Part No. | No. of bit | Maximum
Voltage(V) | Absolute
MAX (V) | Notes |
| MITSUBISHI | M56692FP | 32Bit | 90 | 90 |
|
| M56693FP | 32Bit | 130 | 130 |
|
| M56694FP | 32Bit | 130 | 130 |
|
| M56693GP | 32Bit | 120 | 120 |
|
| M56694GP | 32Bit | 120 | 120 |
|
SEIKO
EPSON | SED2020FOA | 10Bitx2 | 70 | 70 |
|
| SED2020FOB | 10Bitx2 | 70 | 70 |
|
| SED2032FOB | 16Bitx2 | 70 | 70 |
|
| SED2040FVA | 40Bit | 70 | 70 |
|
| SED2000FOA | (G)20Bit, (A)20Bitx2 | 70 | 70 |
|
| SED2000FVB | (G)20Bit, (A)20Bitx2 | 70 | 70 |
|
| SED2800FVA | (G)20Bitx2, (A)20Bitx2 | 70 | 70 |
|
| OKI | MSC1162GS | 40Bit | 65 | 70 |
|
| MSC1162A | 40Bit | 65 | 70 |
|
| MSC7162GS | 40Bit | 70 | 75 |
|
| TI | SN755721 | 32Bit | 130 | 150 | QFP |
| SN755731 | 32Bit | 130 | 150 | QFP |
| SN755721DGG | 32Bit | 130 | 150 | SOP |
| SN755731DGG | 32Bit | 130 | 150 | SOP |
| NEC | ƒÊPD16305 | 40Bit | 180 | 200 |
|
| ƒÊPD16306A | 64Bit | 70 | 80 |
|
| ƒÊPD16326AGB | 32Bit | 130 | 150 |
|
| ƒÊPD16326GB | 32Bit | 125 | 130 |
|
| TOSHIBA | TD62C950 | 40Bit | 70 | 70 |
|
| TD62C949 | 40Bit | 70 | 70 |
|
Ask the above manufacturer for details.
8. Precautions
The data for electrical characteristics,
reliability and lifetime expectancy have been taken based on typical driving conditions.
When designing circuitry, apply the typical rate of driving voltage or,
if the voltages fluctuate, the minimum and the maximum values
of the driving voltage should be set within specified ratings.
Exceeding any of the maximum ratings may cause damage to the display,
or driving below minimum ratings may cause insufficient brightness.
Displays used under anything other than specified conditions
will be defined as out of warranty.
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