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yoni

Tue Sept 15 2009, 10:55AM

Registered Member #2366 Joined: Tue Sept 15 2009, 10:35AM
Location:
Posts: 14

hello everyone.
i am new here and i need some help please..
i want to build my first plasma speaker and i want to know
if any of you guys can help me to find some circuit diagrams or any thing that can help
me built it.
thank you very much
yoni.

Mads Barnkob

Tue Sept 15 2009, 02:40PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Please do yourself a favor and read the forum rules before posting again, do your own research, experiment and ask questions that show insight, this will get you far :)

It is against the forum rules to ask for specific schematics, search google for "audio modulated flyback" or "singing arc" etc and you will find alot of schematics.

yoni

Wed Sept 16 2009, 03:07AM

Registered Member #2366 Joined: Tue Sept 15 2009, 10:35AM
Location:
Posts: 14

sorry about that.. i am new here and i did not know.
thank you.:-D

GhostlyFigures

Thu Sept 24 2009, 01:49AM

Registered Member #2385 Joined: Thu Sept 24 2009, 01:26AM
Location: Waxhaw, North Carolina (Or Charlotte near UNCC)
Posts: 26

Hopefully someone will read this before i give up completely on my project.....
For about a year now i've been testing a couple of plasma speaker designs, trying to get the best one - or at least a working one. Every design so far has had some extreme heating - some of you may know this - So I've been going back and forth with different mosfets etc...

Well recently I remade one and had it working, but I was using my older mosfets with no heatsinks.... yada yada yada --- and I decided to only do quick tests so they wouldn't burn out. Well when I finally get Heatsinks - the whole thing doesn't work now...

I've checked the protoboard, all the soldering joints, and made sure all the components were not damaged, but I have yet to figure out why it stopped working all of a sudden. The design uses a TL494 which seems to be a fav. to a few people out there

well I really don't want to post a schematic - maybe i can post part of it??? (attachment)

Thanks to HVlabs...

In the picture, the mosfets are driven from two transistors driven by the TL494, when first testing, one mosfet would get really hot and the plasma speaker worked quite well.

well now the mosfets are blowing up instantly and nothing is happening with the flyback - i've tested another flyback and tl494 and nothing changed, just blew another mosfet instantly ( I mean as soon as the positive from the flyback center tap is connected to the battery - Mosfet goes BAM) -

Could this be a short somewhere? Is my current going to infinity some how?

{ question here is} What could cause this sudden change in performance, and can anyone help by giving any suggestions or ideas!!!!

tobias

Thu Sept 24 2009, 02:36AM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

First off all I would test the signal going to the FETs

Assuming that you dont have a osciloscope: take the blown mosfets out of the board and put LEDs on their place.. The positive lead on the Gate (G on schematic) and the the other lead on the GND of the circuit. Changing the dead time (changing the position of the pot) the led must change brightness. If it don't you have problems with the transistors or the TL494.

If you have a scope just test the wave of the gate. You need to see something like these:

Post your findings!

If you already have the components, give a shot to this schematic:

It worked pretty well for me.

GhostlyFigures

Thu Sept 24 2009, 03:45AM

Registered Member #2385 Joined: Thu Sept 24 2009, 01:26AM
Location: Waxhaw, North Carolina (Or Charlotte near UNCC)
Posts: 26

Thanks a lot Tobias, The Led test is a great idea, can't believe i didn't think of something like that. The LED's worked as you said they should, both dimmed as I rotated POT clockwise and they dimmed at the same rate and brightness. I thought that the transistors and everything was working correctly because i test the output with a multimeter and got AC (probably the PWM) and DC voltage. Im using a 12v SLA battery, not using 24v that i should be using, but this is only testing, from the gnd to the emitter output, i get 7.55V AC and 3.34DC... (expected i guess?) - now i hope you understand why this is confusing - it works - but doesn't work lol

Mads Barnkob

Thu Sept 24 2009, 04:29AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

A multimeter is really only good at around 50 Hz and up some value depending on quality, another matter, is it a normal or true RMS meter?

Bottomline is, you need a scope to look at waveforms, voltages from a DMM will tell you little to nothing and very likely something wrong.

lpfthings

Thu Sept 24 2009, 01:24PM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Is there anything else on the heatsink that could be shorting it out? I know many components have their cases electrically connected to something, so you may want to make sure nothing is shorting out on it ..

GhostlyFigures

Thu Sept 24 2009, 02:27PM

Registered Member #2385 Joined: Thu Sept 24 2009, 01:26AM
Location: Waxhaw, North Carolina (Or Charlotte near UNCC)
Posts: 26

well thats the thing, i have yet to add the heatsinks, I was about to, but i tested it right before adding them and thats when i noticed something was very wrong -

Its like right when you connect the fets the thing just doesn't want to work. I have even tried it with just one Fet, which worked earlier, but that doesn't even work now. I do have a few new mosfets that im waiting to try because I really don't want to blow those up either.

The reason I rebuilt this plasma speaker was to test different ways to make it run cooler - so I bought several sets of mosfets with different rise and fall times to see if that has a major role in heating - I wanted to find out whether the Fets are staying half off and half on to long.

Thanks for the advice tho, and I do need a scope, but i don't think i can whip out that kind of money just yet, Im a sophomore in college - I could probably get one of the Professors to let me use the Labs to test it out eventually.

Would posting pics of the circuit help? (It could be more confusing then helpful)

tobias

Thu Sept 24 2009, 02:32PM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

Take your circuit to school, try it at the right voltage and take good photos of the circuit, the waveforms (at the primary, gate, tl494) and copy the frequency and voltage at each point...

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