Nope! But regulating 12 down to ~2 with all the filaments connected in parallel will result in ~3 watts dissipation in the regular.
One of those $1 eBay buck converter modules is a good idea, but they're also rather large.
Current regulating each filament individually with a single TO-92 LM317 snuggled up against the tube doesn't seem like a terrible option if I decide against using a switcher.
Idea: if I use a single +12 volt supply, and the graphic EQ IC is using
+12 as its Vcc and +5 as its "ground", the reference output will be sitting at 7.5 volts. I can then use that reference and a single PNP transistor and resistor, with 12 volts on the PNP emitter, to make a current regulator for each filament.+7 volts as ground, sorry, then reference at 9.5 but same idea.
Why not just split 'em up? One sot-23 per filament ain't nuthin'.
40mA x 2 v = 80mW.Cheers, James Arthur
That's the direction I'm thinking...
Cheers
Phil Hobbs
So, one approach would be a boost converter, 5V to 15V, with seven filaments all in series? Or, ground one pin of all the filaments and use a negative converter (many inexpensive buck converters can work this way) to drive the filaments with -2V. Or, just use an oscillator and drive a small transformer, and you can light up the filaments with AC.
A vacuum fluorescent display will need some HV power, anyhow, you might find extra windings on its other power components that can drive the filaments.
put
same size as a to220
-Lasse
The cheap Russian tubes I have in mind are a little weird - they have no heater/cathode, the filament is the cathode. So series connection won't work. And the anode voltages can be as low as 10 volts; I guess they were designed to be driven by SS circuitry.
Those are cute. I'll have to remember they're out there -- although these days it's absurdly simple to plop a switcher onto a board.
I suppose they'd be attractive if you're limited to through-hole.
-- www.wescottdesign.com
Why not just a series resistor from the +5?
You may be able to run the filaments in series, to save power. What VFD V+ voltage will you use?
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
e
or if you don't want to solder and source more components for a few protos than necessary
it doesn't take up much more space and it would probably be hard to find the components alone at that price
-Lasse
Can't run the filaments in series, as they're directly heated. That also means that the current from the anodes must be getting dumped into the filament, so the filament resistance will change depending on how many segments are on. And the "hot" filament resistance isn't well controlled anyway. So I'm guessing if I just use a resistor from a much higher voltage there will be brightness variations?
How does that prevent series connection?
That also
I don't see why the filament resistance would change when a little anode current is added.
And the "hot" filament resistance isn't well controlled
It's not?
So I'm guessing if I just use a resistor from a much higher
In a series filament connection, there will be a brightness variation between tubes because the difference between the anode voltage and the (average) heater voltage is what accelerates the electrons. How serious a problem that is depends on the anode voltage; if it's high, the heater voltage variation won't be a big deal.
Some people recommend running the heaters from AC, or from pulsed DC, to minimize the electron acceleration difference within the tube. I usually run them from DC, and it seems to look OK.
Pulsing the heaters at low duty cycle from 5 volts is efficient. You can turn off the anodes while the heater is being pulsed. So the effective cathode voltage is zero.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
A Skyworks AAT2120 should work nicely.
The inductor can be 3.3uH- efficiency >85% @ 1.8V 300mA.
--sp
-- Best regards, Spehro Pefhany Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8
The maximum DC anode voltage for these tubes is only 20 volts, and I plan to use several, so I don't think there's any margin there. The maximum pulsed anode voltage is 70, however.
Pulsing the anodes is a neat idea, as I have a clock anyway, and could just pulse the anodes and filament antiphase. Any idea what the maximum frequency for something like this would be?
I'm sure they would work at higher frequencies than it's convenient to drive, low MHz at least. It *is* a tube.
Strange gadgets. Do you have an application for these, or just curious?
Seems like LEDs would light up circles a lot easier than VFs.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
~16% duty cycle would give 2V RMS from 5V. But the peak current goes up to 700mA if they're all pulsed at once. Maybe some risk of causing an audible buzz in the audio if it is nearby.
--sp
-- Best regards, Spehro Pefhany Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8
Run them polyphase.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:
I'm working on my little graphic equalizer meter display project.
The graphic EQ IC has a "split rail" reference output and since the supply is 5 volts I'm getting around 2.5, 2.6. But I don't really need this for the rest of the circuit.
I'm thinking about using some VFD "bargraph" indicator tubes for the display. The ones I have in mind need a filament voltage of around 2 volts at about 30-40 mA each, times 7.
I'd like to just slap a transistor fed from that reference on the base to regulate the filaments... 5 volts in on collector, ~2 volts out, just under 1 watt dissipation.
Darlington NPN will have too much B-E drop to work here. Can anyone suggest a suitable jellybean tranny for this purpose?
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