Type: Driver
File Name: vfd_filament_10669.zip
File Size: 13.5 MB
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Archives August Blog at WordPress. Post to Cancel. By continuing to use this website, you agree to their use. Insufficient voltage causes unstable thermionic emission and leads to degradation of display quality. The rated filament voltage vfd filament be carefully maintained. If the filament potential is lower than the anode and grid cut off voltage, thermionic electrons can reach the anode and cause illumination of the phosphor. The filament bias voltage should vfd filament increased to prevent this problem.

The LM will work down to 2V. If you are building a general purpose VFD PSU for experimenting with, vfd filament may be worth powering it from an adjustable LDO regulator so you can 'dial in' the desired vfd filament voltage. Excellent advice Ian.

I am hoping to build with at least three vfd filament displays. I don't believe I will need to vary the filament voltage greatly, but making it adjustable from vfd filament start may be wise.

Rolo's solution uses series resistors to do that. I vfd filament a clock using DG8 in the 70's and was dissipating almost 1 watt dropping the filament voltage. The GC as designed dropped That could well be vfd filament V3 design!

Building a VFD filament driver: Part 1

Making the filament and HV adjustable on the board. Did some measurements on the LM, that gives an idea on what you can expect with different vfd filament voltages, this is without the two series resistors. The enable function for the filament can be tricky when using LDO before the LM, the input must not exceed the Vcc of the chip. Shifting this function to a LDO with enable input or maybe use an optocoupler as level shifter here, have to give it some thoughts. Unlike driving a multi-digit 7-segment LED displaydriving a VFD is a little bit more complex due to the multiple voltages involved and the relative potential requirement for the filament.

Of course there are many specialized chips we could use to build a VFD driver with, but like with many of my previous projects I love to build things from scratch so I thought I would build the filament driver and the VFD driver myself. This offset voltage is necessary to prevent ghosting see this app note for more detailed explanation. Also in order for the illumination to be uniform, an AC drive current waveform from a vfd filament transformer is desired. A typical filament driving waveform is illustrated below:.


Fortunately, we can generate this waveform vfd filament biasing vfd filament center tap of a pulse transformer above the ground and feeding a square wave through it. The following circuit design shows such a filament driver circuit using a timer and a center-tapped transformer.


The timer is configured as an astable oscillator. Given the RC values chosen 1k, 4.

The pulse transformer was hand-wound using a torroid core. Because the operating frequency is relatively high, only a few turns are needed for each winding as a result. Using the values given, the measured Vfd filament voltage across the filament is at around 2. This in turn eliminates the ghosting effect. Figuring out the actual pinout of the module is relatively easy. However, this limits the input voltage to 3. Early Monday morning I placed an order with Mouser for the parts to breadboard this circuit. The center — tap technique is used to prevent luminance slant i.

Using a transformer without this center-tap can not only cause luminance slant but also ghost illumination due to exceeding the amplitude of the filament voltage in excess of the specified cut-off bias voltage rating. In the case of a DC or battery power supply, a pulse wave form for the filaments can be generated from a DC to AC converter.

Insanity New VFD Filament Driver

The concept of pulse voltage supply to the filament is the same as AC filament drive. Please note that the pulse voltage should be calculated as an RMS vfd filament mean square vfd filament from the wave form as shown in formula 1. A frequency range of 10kHz to kHz is recommended. If a DC filament drive is adopted, a potential difference between the anode and grid voltage will be apparent as a luminance slant across the display as shown in Fig.

This shows brighter luminance at one side of the display due to the DC voltage drop.Luminance varies with the filament voltage (Ef) as shown in Fig Since the lifetime of a VFD is dictated by the extent of evaporation of oxide materials coated. If you remember my last VFD clock, I attempted to design an AC filament driver for the display. I searched online for a solution and discovered the LM VFD Filament Driver. Like the name suggests, it's specifically design to vfd filament an AC signal to VFD filament from a DC source.


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