Picture of 555 timer based plasma speaker

This instructable will show you how to make an audio modulated plasma speaker using a flyback transformer out of an old CRT display, and the all time hobbyist favourite which is the 555 timer chip.

Not only can this circuit be used to produce audio modulated plasma arcs but it functions as a high voltage power source for other projects.

I will be updating this instructable over time.

Note: Please turn up your sound volume, it sounds much better in real life but my camera does not pick it up too well.

You may not, except with our express written permission, distribute or commercially exploit the content. Nor may you transmit it or store it in any other website or other form of electronic retrieval system.
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Step 1: What you will need

Parts list:

1x Flyback tranformer

A flyback transformer, sometimes called a line output transformer are used in CRT TV's and computer monitors to produce the high voltage needed to power the CRT and electron gun. They also have other auxiliary windings built into them that power other parts of the TV.

You can get flyback transformers out of older CRT monitors and TV's. They are the ones that have a big chunky chassis. There are also other instructables on this website showing how to remove them from the chassis and circuit board.

1x Power MOSFET,
I used an IRF540 as that is all that I had lying around. I strongly recommended using a MOSFET with a higher drain-to-source voltage than the IRF540, which is only 100v.

Just for an example IRFP460 would be well suited for this and IRFP250N and IRFP260N would also work. Any MOSFET that is rated for high voltage, has a low on resistance and can take more than 15 amps would be fine.

1x Heatsink

You will need a large heatsink as it will get very hot (more on why later). The TV board you got the flyback from is a good source for heatsinks.

1x NE555 timer chip

I also recommend using an IC socket (8 pin) for the 555 so you can easily remove the chip without de-soldering it.

2x 47 ohm resistors

1x 22 ohm resistor

1x 470 ohm resistor

2x 50K potentiometers

3x 1nF capacitors

1x 220uF - 1000uF electrolytic capacitor (16v will fine).

1x 10nF capacitor

1x 100nF capacitor

1x fast diode, such as UF4007

1x NPN and PNP complementary bi-polar junction transistor pair (if you are following the first schematic). BD139 and BD140 can be used here.


12V power source

Fuse (recommended to protect the power source/supply).

Audio source (This could be an MP3 player or old phone for example).

Solder and soldering iron + some spare wire.

I am in no way responsible if you mess up with this circuit. If you mess up, receive an electrical shock or burn your house down whilst making this circuit you have no-one to blame but yourself. By following this guide in order to make this circuit you agree to accepting all liability if something were to go wrong.
NullByte45329 months ago

I've tried to make this thing, but I failed. Firstly, it did not work at all, but after a few seconds my flyback exploded. What am I doing wrong? Should I wind primary of flyback myself, I mean before I used unmodified flyback from an old tv. Everything looks pretty well assembled (not as I always do:)), powered by an old ATX power supply. I've also tried with ignition coil, but that did not work. Ignition coil heated up just a bit, but transistor was cold. And what specific type of capacitors should I use?

ljeckel1 year ago
I tried to adjust potentiometers (100k not 50k) still not bigger. I tried 8 turns too, no improvements.

I don't understand what you mean by "are the cores spacers still inserted between the core halves?"

So the diode I'm using is not what's causing the problem?
ljeckel1 year ago
Hi! I built this project but my arc is pretty small (1,5 cm max) i'm using a 12v 20 amps atx psu but i measured only 2-3 amps on the primary. The primary coil doesn't even heat up! i use small wire i did 10 turns for the primary. I tried to reverse the polarity, it was smaller. I'm using a 6 amps mosfet for now. Could it be the diode ? i'm using a By329 which isn't as fast as the uf4007 (135ns). Using the best schematic. Sound is very weak too (due to the small arc I guess). Can you help me here please ?
Alex1M6 (author)  ljeckel1 year ago

Have you tried adjusting both of the potentiometers? as there will be a "sweet spot" where the flyback will produce the best arc. If you have already done that then I would also try removing some primary turns, perhaps try 8 turns.

Also are the cores spacers still inserted between the core halves? If not then they need to be.

The audio volume can be greatly improved by using the pre-amplifier on step 9,
sleepyjz2 years ago
I built this, the circuit seems to be running fine (the heatsink + fet also make a great fast acting personal heater!). I tried a cassete player for and a CD walkman, both dated technology but it was just to test the stuff. The problem is, the audio is VERY quiet and I'm not sure why. It's nothing compared to the volume you got going with your arc in the video. It's almost concealed by the noise of my power supply fan. I'm using the BEST schematic with two supplies.

Any Idea what's going wrong with the audio? I'm using right channel and ground, headphone wire continuity with the circuit is solid. Tried a couple of different flybacks too.

You have got to see the results of using this driver with a "sampo" brand computer monitor flyback.....Internal capacitors are scary as hell. Youtube channel coming soon :p
Scratch that. A boombox plugged in to a wall delivers good volume.

I noticed that too.

It looks like the pre-amp is important. I tried a late 80's Sony Walkman...nice blaring audio compared to modern (lower power) audio output. A more robust audio source the better. Have not tried added pre amp circuit, but that looks like a good idea.

As a check, before you hook up the Xfrmr, you can hook up an 8ohm speaker on 9V in place of the Xfrmr. You can hear the oscillation from the 555 and even tune it abit using the 2 pots. This will verify your 555 wiring and verify the xstrs and FET are working.
radio man1 year ago
u spell favorite with out u
Alex1M6 (author)  radio man1 year ago
Not in the UK we don't.
PCBgroove1 year ago
From all the comments I see here, its lack of electrical engineering going on. My experience with mosfets is the RDS lends to dampening or raising ringing in the feedback loops. That will kill you every time and lead to hot Mosfets. You have to know what your doing with these and sizing cooling based on a non ringing circuit. Additionally, I would use an led and a receiver to decouple the 555 from the output circuit too and remove the danger of electrical shock hitting your telephone with 2000 volts. Another thing too are the back emf's these are transient based and can lead to slowly destroying your output mosfets. If the frequency can be adjusted to limit say at 8 khz, IGBT's are your best bet. Then the problem is the 8khz can be heard. If still using mosfets, you better spend a few hours looking over all the data sheets information, have a engineering background to deal with this and better buy perfectly matched transistors in your paralleled output circuit. Your output is only as good as the weakest link as all the power will be sucked there and then the projects really sucks. I think its neat what your doing but its a science fair project. Otherwise Sony would already be building this.

Why not work on the real issues the sub-woofers that are very expensive, and amps to drive them. The mid-range and tweeters have already been figured out.
S3 will work better if you add a 1200~2200uf Cap rated at main voltage x2 to the main line.
as close to the fly-back transformer as you can so Base of Q1 and 12V main at the transformer. ..

and adding some type of clamping on the transformer feedback might help make the sound a lot better but will make the arc smaller.
high speed diode like UF4007 and a 2ohm 1 watt resistor in series across the transformer P-coil might make for quick and easy testing good testing.

let me know how it go's if you test the ideas ;-)
Could I ever wire this circuit to audio modulate a tesla coil? I need help somebody please guide me. Haha
Alex1M6 (author)  WeaponsofmyMind001 year ago
It wouldn't be very efficient using this design. Head on over to the 4hv forums for questions and I am sure the community will able to help.
mmcnater1 year ago
I have a 30V, 5A DC power supply. Do you think I could just connect two jumpers at the inputs to the circuit to the single output of the supply so the voltage divides, or would that cause a problem?
Alex1M6 (author)  mmcnater1 year ago
Hi I am not quite sure what you mean here, could you describe what you are trying to do in more detail.

Do you mean just using the 30v supply for both the 555 timer directly and flyback? if so then that will not work since the max voltage the 555 timer can run off is 16v for most versions of the chip.

If you put a voltage regulator such as the LM7815 between the 30v supply and 555 timer then that would work, just be sure to use lots of decoupling capacitors and a fuse between your power supply and circuit.
dude can i use 1n80 mosfet(800v N channel) instead of IRF's and is there any other diode instead of UF4007
Alex1M6 (author)  MadGuitarist1 year ago
The on state resistance of that MOSFET is too high for the voltages being used in this circuit. Any fast recovery rated diode can be used in place of the UF4007, just make sure it has similar ratings.
what about using a 12v adapter
grobgrobin1 year ago
thanks i thought it was me being thick
Alex1M6 (author)  grobgrobin1 year ago
I think I might have had a bit to drink when I uploaded it ( : Now I wonder how many peoples circuits haven't worked becuase of this mistake.
grobgrobin1 year ago
hi there in the best set up u got Q3 pnp with arrow come out at the bottom and when i look on ebay to buy one it shows a npn with arrow coming out tho bottom is Q2 and Q3 number mixed up
Alex1M6 (author)  grobgrobin1 year ago
Your right! Looks like I made a mistake there, I will correct it.
phevtron1 year ago
greetings and congrats for your excellent and clear guide.
i really wanna know if the irf640 with vdds=200v and ID=18 amps at 25celsius
is suitable for this project , here is the schematic so you can take a look

thank you very much :)
james346021 year ago
Can I use a 24v input at Primary Coil and MOSFET section
Alex1M6 (author)  james346021 year ago
Yes, but you will need to use more primary coil turns.
budhaztm2 years ago
What about this mosfet :

love the instructable. great job
Alex1M6 (author)  budhaztm2 years ago
That looks fine ( : Make sure you try an RCD snubber too to protect the transistor.
sternmin8or2 years ago
So I just built essentially this circuit except the transformer is on a seperate power supply. When I hook it up to the transformer i can hear a faint humming sound that goes away rapidly. When i hook it up to a 8 ohm speaker the sound seems to dampen. If I touch the mosfet heatsink while the speaker is dampening it seems to become louder again.

I am using a 12v cpu power supply capable of several (around 12) amps. Is the capacitor across the mosfet important because I do not have it in my circuit. What does it do?
I have discovered the problem. I was using a 9v battery to power the seperated 555 timer circuit, however I had a buffer stage in it and for whatever reason the buffer stage and the 9v do not like eachother (at all). Which is why it dampened. When I touched the mosfet I gave it some form of extra grounding (maybe?).

Long story short: 9v batteries were the invention of satan and should all be destroyed
Alex1M6 (author)  sternmin8or2 years ago
Glad you got it sorted ( : I did mention battery's on step 4 briefly

An NPN and PNP totem pole BJT buffer stage? If so I think possibly the high peak current draw of the gate charging might have drawn down the 9v's so much that the voltage sagged. Also you might have shoot-through happening and both BJT's turning on at the same time causing the 9v's to short.

Also if you are using separate supply for the 555 and flyback (which I recommend) then remove R4 and make R3 22 ohms. This will help switch the MOSFET faster.

Never mind, I was completely wrong. A battery would have worked just fine If i had attatched the two power supply grounds together. I had forgotten that the current to the mosfet gate had to get back to the negative terminal of the battery D:

The diode and the capacitor across the mosfet are to prevent surges? Or do they help keep the mosfet cool/increase arc length? I have a 500v mosfet so i dont think I need to worry about surges, but if adding those components will make the arc better then I am all for it,
Alex1M6 (author)  sternmin8or2 years ago
lol, I guess you can say you learned something about how MOSFET's work whilst making this ( :

The diode and capacitor is there to help reduce the back-emf voltage spikes that will be produced on the primary side when the MOSFET turns off (its also one of the reasons the MOSFET gets so hot because it is avalanching every cycle).

You *might* be ok with that 500v MOSFET but its always good not to let the MOSFET's breakdown voltage be the only thing protecting it. If your MOSFET does blow then you need a larger capacitor here.

I have also found putting a small MKP capacitor in parallel with the primary coil helps reduce the voltage spikes and MOSFET heating a little. It makes the arcs smaller but thicker though.

As for making the arcs smaller, putting anything there that reduces back emf spikes will make the arc slightly smaller but its a compromise between arc length and durability. The only reason you get such a high voltage on the secondary coil is becuase of this back emf spike, if you were to put a diode in reverse with the primary coil like you would with a motor or relay then you would remove all back emf spikes but arc length will be much smaller becuase there will be no "flyback kick" to further boost the output voltage.

I also recommend having a permanent arc gap set up for the arc to take place, rather than always drawing arcs and moving the arc around. I say this becuase the back emf spikes are different depending on how much you are loading the secondary coil of the flyback, and with no arc at all or if the arc is unstable the back emf will much higher than if you had a steady arc going.

Hope this helps.
-max- Alex1M62 years ago
so would a capacitor / diode in series be the best to put across the primary to keep the back-EMF at bay?

i was thinking, what if you put the diode in between the primary and the transistor? like

+12V -> one side of primary -> other side of primary w/ small capacitor across it -> DIODE -> mosfet with backwards diode-> ground.

and also have zener diodes put together across the gate, so any overvoltage (<24) to further protecy the mosfet?

and havee you tried IGBT's? do they work any better?
Alex1M6 (author)  -max-2 years ago
Sorry I have missed your comment up until now. The way they commonly do it in commercial power supply's that use the flyback topology is to put an "RCD snubber" in parallel with the primary coil. This dissipates the energy stored in the leakage inductance of the primary coil and thus prevents the back emf voltage from raising above the MOSFET's max breakdown voltage. The MOSFET getting hot in this design is mostly caused from avalanching.

Yes you can use a zener diode to protect the gate, use a 12-18v one with cathode to the gate and anode to ground.

See the image I have attached.
RCD snubber2.jpg
jukees2 years ago
Hi, is Irfp250 suitable for this project, (200v 30A Rds(on) = 0.085).
used it in the plasmana's ZVS flyback...
Alex1M6 (author)  jukees2 years ago
Yes that MOSFET will be fine. Its almost identical to the IRFP260 but costs less ( :
Airazz2 years ago
My local electronics store has both NE555D and NE555N timers. Is there any difference which one I use? The price is the same.
Alex1M6 (author)  Airazz2 years ago
Hi, yes there is a difference. They are both the same chip but the NE555D is a much smaller version and are a complete pain in the ass to solder by hand.

See the image I have have attached to this reply for comparison.

Short answer: Get the NE555N.
555 package.jpg
Airazz Alex1M62 years ago
Oh, good to know. Thanks for the advice.
baven2 years ago
Hi there i got a problem with this circuit. I adjusted the frequency and Im using
the BEST schematic but when I turn on the 555 oscillator and connect the primary
coil to power it gets very hot and no arcs on secondary. Any idea where the
problem could be?
Alex1M6 (author)  baven2 years ago
Can you check your MOSFET is not shorted and that the 555 timer is outputting a square wave?
sleepyjz2 years ago
Just some advice for powering this driver (the BEST schematic). I am using an ATX and a lead-acid battery as the two supplies. If you are doing something similar, do not use the lead acid battery on the flyback side of things. With the amount of heat the FET gives off, the battery will drain very quickly - use the battery on the 555 timer side and a mains-driven power supply on the flyback side. I'm waiting for another ATX to show up so I can do away with the SLA battery, however a 12 volt battery charger is good too, but It was fussy on the flyback side though.
kshah92 years ago
Hey, Nice Instructable.. I need some help with the flyback transformer, mine looks similar to the one in the instructable.. but i need to know, do you need to take care of the polarity for the primary windings?
-max-2 years ago
i am working on this, you can see my instructable on it called "build a singing arc (plasma speaker) (ongoing project)"
-max-2 years ago
is it possible to make the 555 circuit w/ distinct frequency and duty cycle control, instead of one controlling both, and the other controlling just frequency?
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too bad, cool inst. sent friend somewhere else...
do you still have the old circuit Schematic somewhere? im trying to built that only only, seeing i ordered parts specifically for that schematic
Alex1M6 (author)  greenman22882 years ago
Its the third image on the schematics page.
what does "nf" stand for in caps? I thought it was uf....
Gofilord3 years ago
Is there any replacment to the flyback transformer? I can't find it anywere!
-max- Gofilord2 years ago
you can try an ignition coil, but the arks may be smaller and hotter...
Alex1M6 (author)  -max-2 years ago
Ignition coils would not work very well for this, the core in an ignition coil is iron and the switching frequency's involved with this circuit need a ferrite core.
-max- Alex1M62 years ago
i know. but i have seen it done... yes at those freq to. of coarse the arcs are much smaller, and its not the best replacement. but the freq can be lowered. (but youl lose the plasma spkr epicness)
Alex1M6 (author)  Gofilord3 years ago
Not really no. You might be able to use one of those yellow switching transformers if you keep the voltage low but you will have to draw the arcs out.

You would also need to figure out which are the primary coil pins.
mochonacho2 years ago
Where can I find a flyback and a MOSFET for cheap?
go to jameco electronics and find an irf 740 or irf 840 among those lines. ebay is ok for old hard to find flybacks but if you dont want an older AC flyback then get a old (preferably B/W) crt tv
Alex1M6 (author)  mochonacho2 years ago
Ebay I guess, but try and find an old CRT TV or monitor. You can usually get them for free now.
Sky Graham2 years ago
Hey, the circuit diagram shows the primary coil connecting to the Drain of the Mosfet, and the Circuit that you drew has the primary coil connecting to the Source? Also, forgive me but, whats the component between the Drain and Source with the arrow?
Alex1M6 (author)  Sky Graham2 years ago
I checked and it is defiantly connected to the drain in both diagrams, which is what it should be connected to. The arrow on the traditional schematic is the MOSFET's built in body diode which is in reverse with the MOSFET. This diode is quite slow so you might want to put a UF4007 or something similar there instead which is faster.

I am going to post an updated version of the schematic on here soon which will help with lowering the amount of heat the MOSFET generates.
mspearin2 years ago
Okay so I built the who thing and when I plugged it in it didn't turn on I did a voltage reading and it said that the 12 volts went down to about 2.3 volts. I tried adjusting everything and than replacing the power supply ( its a 120 to 12 volt at about 5 amps). I checked the whole thing for shorts and couldn't find any. Do you have any ideas what it could be. I am guessing it is the power source. Would a small car battery work or would there be to many amps and fry the thing??
mspearin2 years ago
I have a KA555 Chip will that work?? Also a IRF530 MOSFET will these work?? I am new to these chips so i don't know much about how they compare.
Alex1M6 (author)  mspearin2 years ago
The KA555 will be fine, and the MOSFET looks ok to me.

sunshiine2 years ago
I tried to vote for this. Which contest did you enter? By the way I saw your utube channel. Very interesting!
Alex1M6 (author)  sunshiine2 years ago
Thanks! I can't remember actually, I think it might have ended now anyway.

slewis193 years ago
Hi, I have made according to the colourful diagram and it does not work? Is it the same? Cheers, Sam
Alex1M6 (author)  slewis193 years ago
Yes there are both the same, apart from the decoupling caps across the supply rails although that will not make any difference. I would say follow the traditional schematic as it is less easy to get confused and there is less mess.

Have you made sure all connections are soldered securely and that there are no short circuits anywhere? Also what MOSFET did you use? What is your power supply voltage and how much current can it deliver?

Did you try reversing the polarity of your primary coil connections then doing a sweep of the frequency range via the potentiometers.

Hi, I used the EXACT mosfet as you did, My power supply is 12v battery with 18 amp current. I am using a transformer from a large industrial printer that looks the same as a flyback.
Alex1M6 (author)  samjameslewis3 years ago
Hi, it is hard to tell by the pictures but it looks like you might have the potentiometers shorted out as there is solder across all 3 pins.

Do you have a frequency counter of some sort to test if anything is coming out of pin 3?
Hi, I checked the pots, the middle and one side pin are connected as in your diagram. Would an oscilloscope work? Between pin 3 and ground?
Alex1M6 (author)  samjameslewis3 years ago
Yes you can use an oscilloscope to measure the waveform, just be sure to put something in to limit the current. I just use my multimeter that has a frequency counter mode to measure if the chip is outputting any frequency.

Also you will need to remove the MOSFET in order to get a reliable reading.

Really go over the circuit and solder traces as I am sure it is just a simple wrong connection somewhere, I always make at-least one mistake when I follow schematics!
Thank you!.. :), I will post when I get working. Cheers, Sam
-max-3 years ago
tie the two audio channels together for true mono, and i wouldn't use a phone, but something like a Walkman.
bart4163 years ago
A few comments to increase the performance (and lifetime) of the circuit.

You're actual circuit diagram has a mistake in it (the decoupling capacitors are placed incorrectly).

You're missing a FET driver. These power MOSFETs have a fairly large gate capacitance. Most logic ICs can't provide enough power or sink it fast enough for that matter to switch these. Also, you need to avoid keeping your FET open for longer than a few microsecond. Else it will heat considerably faster resulting in damage, up to the point where the junction is destroyed due to heat. Just pick any FET driver for this, a 48 kHz isn't all that fast anyway.

Add a large resistor (1M and up) between the gate of the FET and ground to remove the charge from the gate quicker and to remove the charge when the circuit is switched off. Else the FET might be open from the start resulting in a larger spike on the power supply.

While your coupling is logical. You should realise it's still a high voltage device, and in most cases music players are fragile. You will need to use an optocoupler like an IL3000. See the datasheet if you don't know how to use it. The circuit you need is on the first page most of the time. Obviously you should use different sources for the input and the output opamps if you do this, else it's a pointless endeavour.
Alex1M6 (author)  bart4163 years ago
Thanks for the feedback. I know I missed the gate drive part out but I was trying to make this as beginner friendly as possible.

What pair of matched transistors would you recommend for driving the MOSFET gate?

Should the decoupling caps go directly across the supply rails?
bart416 Alex1M63 years ago
FET drivers do seem scary to most people. Luckily they started making those easy 4 pin drivers. Though they might be a bit harder to get for people not familiar with ordering components. The thing is, this circuit does live a lot longer with a FET driver. Having made similar ones myself in the past I've noticed a lifetime increase from a few hours to hundreds of hours. Usually it actually failed due to the flyback transformer being done for.

If you are going to use transistors to drive the gate, take a matched nmos-pmos pair. If you use BJTs you risk them being on at the same time. With FETs you have the threshold voltage to keep you somewhat safe. Though it's hard to recommend what to use. I use the highly scientific method of using whatever I find on my desk/in my drawers.

And as a rule of thumb you should decouple your power supply and all logic ICs that switch. The 555 pretty much acting as an oscillator here means it qualifies for that criteria.

The values are trickier. I generally tend to use multiples of 10 myself cause I can find a lot of those around the lab. But it really depends on your application. In this case, on the power supply rails don't be afraid to go high value. Just be sure the initial charging of the capacitor doesn't overload the power supply. But considering how much current the flyback needs that sort of irrelevant here. Hence, any big fat elco will do. On the other hand, you should add a small 1nF (or any arbitrary value, not too big though) ceramic to that. Though not strictly correct you can see the ceramic as a charge supply to provide for fast switching and the elco is somewhat "slower". The actual reasons are to be found in the non ideal behaviour (Troubleshooting Analog Circuits by R. Pease has a nice chapter on non ideal behaviour of capacitors explained in a simple way). In this case the 555 becomes trickier. Generally a 555 is fairly low noise so any small capacitor will do. But here you'd have to test it with a scope cause I'm not sure how a 555 behaves under heavy load.
Alex1M6 (author)  bart4163 years ago
I am using a 12v lead acid battery for the power supply so heavy current draw is not an issue.

What I meant with asking what type of transistor pair to use is would those small bi-polar transistors you get in disposable cameras be suitable, or are they too small for this purpose? I have found both npn and pnp's on them and after googleing they appear to be matched/complimentary pairs.

I think in future experiences I will use separate 12v battery's for both the flyback and 555/logic. Although I do not have a oscilloscope myself, I came across a video on youtube where the guy showed the waveform with and with-out the capacitors.

With-out the capacitors the waveform of the 555 output distorts when drawing arcs and with them it is much cleaner.

I have only managed to kill one flyback and that was with my ZVS driver @ 36v input, the ground pin arced to one of the low voltage windings.
bart416 Alex1M63 years ago
Well, the current draw can still cause a drop in voltage. Even with batteries, the capacitors will compensate for it. Well, if you wish to see what's -actually- happening you should simulate the circuit in LTSpice. The internal resistance of a car battery is about 0.01 Ohm when being heated if my memory serves well. Considering the terminals and so on, Put a 12V voltage supply with 1 ohm resistance.

As I said earlier, using a NPN-PNP push-pull configuration is problematic as driver. You risk short circuiting the battery by doing so. Anyway, you need to figure out how much current you need. Lets assume a 1 ohm resistance of the power supply and a 2nF capacitor. The capacitor voltage is 12V*(1-exp(-t/(R*C)). We assume a capacitance is charged after three times RC. So it takes 3 times R*C to charge the capacitance. 6 ns to charge the gate capacitance assuming an ideal step from the 555.

Sadly the 555 doesn't output an ideal step, in fact it takes about 200 ns for the signal to rise! This is why ideally you use a PWM chip designed for faster operation but lets stick with the 555. Modelling this isn't exactly fun. So lets assume it ramps up in a linear fashion. Now you can solve this with differential equations and nicer methods but lets use laplace for this. The system function is 1/(R*C*s + 1). The input can be modelled as 12V/(200ns) * t (u(t) - u(t - 200ns)) + 12 * u(t-200ns). The laplace transform of this is less fun sadly, since I don't wish to torture you, I suggest the usage of MATLAB or Maple. Multiplying the two gives an even more fun equation to return to the time domain. Now the response to that I'm not even going to type here due to its length. We know it's charged if the voltage over the capacitor reaches 12*(1-exp(-3)). This results in t being 192ns meaning the maximum frequency you could switch at is 5 Mhz (interesting result in case you wish to use a faster method to drive the FET in later more advanced circuits, though in that case you'll also have to consider the fall time). Now we need to know the current though. Taking the expression for the output voltage over the capacitor and the fact the supply provides 12V you'll see it starts with a peak of 12A and only drops to what we can consider 0A past 200ns. Meaning your BJTs will need to be capable of supplying a burst of 12A. Check the datasheet of the BJT to see if it's suitable for it as I'm not familiar with the discharge circuit of a camera. It's worth a try anyway if you have enough spare parts.

And the output of the 555 distorts without the capacitors for a few reasons. First of all, all logic ICs have switching noise. This is inherent to the way TTL and especially CMOS logic is built. Second of all the transformer will cause inductive spikes on the power supply rail. Now drawing arcs causes some additional effects. Not to mention the inductance in close proximity due to drawing a few ampere isn't to be ignored either.
moris_zen3 years ago
Just remembered - I tried using the 8 external as primary and it didnt work so I used the primary inside the Flyback - worked much better.
Alex1M6 (author)  moris_zen3 years ago
What voltage and max current can your power supply put out? As depending on the frequency and duty cycle you choose, a primary coil wound on the core can need around 7-10 amps to work its best with this driver.

But I guess it could also be dependant on the flyback you use.
I tried a computer PS that should give over 10amp but it doped to 10V and gave much less current then specified (may be I need to short all the 12v outputs?)
IDK ??
moris_zen3 years ago
I used an IRFP2907 (rated 206Amp 70V) - I used two whte LEDS in reverse polarity of the primary coild to prevent over voltage burning the FET .
I also added a CPU HS with a fan keeping the FET nice and cold - can run for hours now :-)
Hope this will help someone .
Nice instuctable!
Alex1M6 (author)  moris_zen3 years ago
Hey that is a good idea, but are you sure it does not dampen the arc length too much? As my understanding is that the negative HV spikes that appear on the primary is what causes most of the high voltage on the secondary.
well .. 1 diode did dampen the arc - I used 3 - then there was no difference .. then I replaced them with a 220ohm resistor - had same affect (cant have a large spike over that res - it would make impossible currents).
What is the model number of this flyback you are using? thanks!
blindpyro3 years ago
Hey great job, if I may make one suggestion though. I do sound work for a living and I believe you would be better off summing channels left and right. Or simply using a mono 3.5 mm plug.
Alex1M6 (author)  blindpyro3 years ago
Hey thanks for the suggestion! I never actually tried that.

I have one for you, are the separate audio channels both positive voltage with respect to ground (the return conductor) or is one positive and the other negative voltage?

I think if you were to use a pre-amp to boost the audio signal before feeding it to the 555 chip it would make the audio much louder and more defined as the 555 isn't really sensitive enough to do this on its own with just the small current an mp3 player or phone outputs that is usually intended for in ear headphones or a docking station with an amplifier stage built in.
Yes they are both positive, and yes I think an amp circuit would benefit. I suppose an op amp would do and you could even use a dual band op amp to add gain to each channel then combine them as they come to the 555 circuit.
Gofilord3 years ago
Hy, This is one of the cooler builds on this website and I am defenetly going to give this a go.
Will a 12V wall adapter work? if so, how much current do I need it to have?
Alex1M6 (author)  Gofilord3 years ago
Thanks. You can certainly try it but I don't think it will work too well as this circuit needs at-least 5 amps to really get a good arc. Most 12v wall transformers will get hot and eventually burn up if you try to draw more than 1 amp from them.

Do you have any 12v lead acid battery's? They work very well for this circuit.

Also you can use an old computer power supply if you have one lying around, the 12v rail can supply a decent amount of current easily. You will just need to jump start the power supply's on signal wire to ground in order to get it running with out a motherboard.

oni3 years ago
I just made this and it works really good. Thanks for posting such a good instructable. Do you have any tips for tuning it?
Alex1M6 (author)  oni3 years ago

Turn one of the pots all the way down and turn the other pot as the circuit is on. Then turn the first pot slightly and turn the second pot all the way around again, just keep doing that as it should help you find the sweet spot. Also once you have found it try switching the polarity of the primary coil connections and see if it makes the arc any bigger as these flybacks will work best on one polarity.

Also could you post a video of it working if you get chance? And does your MOSFET heatsink get hot at all?
oni Alex1M63 years ago
Thanks for the tips.
I have an 80*80mm Aluminium heatsink I pulled out of something that jas a computer case fan on it (I dont think it makes a diffrence though) and that gets pretty hot. I think i will cut out a new larger heatsink for it. I can take a video, ill post it here sometime later.
Alex1M6 (author)  oni3 years ago
Try changing the R3 and R4 resistors to something lower to help the MOSFET saturate quicker.

I have even heard of people using no resistors for the gate at all.
oni Alex1M63 years ago
interesting, Has anyone put potentiometers instead before?
Alex1M6 (author)  oni3 years ago
Not sure, but they would have to be very small potentiometers (less than 100 ohm) as they are only really there to stop parasitic oscillations that can destroy the 555 chip.

I just had an idea, a Schottky diode in reverse bias with the gate resistor in order to quickly drain the gate charge when the 555 goes low. It might help the MOSFET turn off quicker.
oni Alex1M63 years ago
You sir are what they call a genius.
On a side note i found out that I didnt plan out my PCB to well. It has really thin tracks so with all that current it decided that it wanted to get really hot. I have resolved the issue by putting a layer of thick solder on the tracks.
ZygOhm3 years ago
When I'm testing this circuit, my breadboard is melting :DDDDD (Current about 5A using 12V) but it works !!!!!! :DDD
Alex1M6 (author)  ZygOhm3 years ago
Haha, I recommend soldering everything onto a piece of strip board if you can, especially the MOSFET as that area passes too much current for the breadboard to handle ( :

You could leave the 555 timer part on the breadboard and just solder the MOSFET connections.

You can also try lowering R3 and R4 resistor values to see if that helps the MOSFET gate saturate faster.
oni3 years ago
In the parts list you have 2x 1nf capacitors but on the schematic it has 3.
Alex1M6 (author)  oni3 years ago
Thanks for letting me know, I have corrected it.
oni Alex1M63 years ago
I only realised when I had bought all the components and then started drawing up the circuit board and noticed that i was missing a capacitor.
Alex1M6 (author)  oni3 years ago
You can leave the capacitor from pin 5 to ground out if you want.
oni3 years ago
Would this circuit run off a car battery?
Alex1M6 (author)  oni3 years ago
Yes, in fact a 12v car battery is probably the best thing for powering this circuit.

I myself used a lead acid battery (the same type of battery as a car battery) to power this circuit.

Just make sure that you put a fuse in-line (13amp mains fuse is fine) with the positive wire from the car battery to protect it if something were to go wrong.
Can I use the flyback from CRT screen monitors?

Also, Can this be powered with 9 volts?

Awesome simple project.
Alex1M6 (author)  blinkyblinky3 years ago
Yes any type of flyback transformer would work fine for this ( :

Are you talking about a 9v battery or a 9v power supply?
A nine volt power supply.

Also, can I use a small audio transformer for a lower voltage?

And, by secondary do you mean the one with more turns or the one with less?
Alex1M6 (author)  blinkyblinky3 years ago
Yes, well, as long as the power supply can supply at-least several amps.

I would not recommend using anything lower than 9v (preferably 12v) for this circuit as you will not get much of an arc from the flyback with anything lower powering it, so whilst you can use an audio transformer to lower voltage I would advise against it.

By secondary I mean the one which will be the output end (for a flyback this is the one with more turns).
Awesome project, maybe I can use this to prove to my brother that you can use a teslacoil to produce sounds/music.

Would that give a nasty shock it looks like it really would XD
Alex1M6 (author)  the_burrito_master3 years ago
Thanks ( :

I am not actually sure how much of a shock you would feel at the frequency of the arc is higher than that of a humans nervous system, but, the arc is VERY hot and will leave you with nasty burn marks.
OH, hmm sounds kinda crazy :D
Alex1M6 (author)  the_burrito_master3 years ago
haha ( :
bkrei3 years ago
Have u used the Trafo from the old TV's? (no Flatscreen)
Alex1M6 (author)  bkrei3 years ago
This is one CRT TV I took a photo of whilst taking it apart.

DSC_4701 - Copy.JPG
Alex1M6 (author)  bkrei3 years ago
I am not sure what you mean by "Trafo" but I assume you mean transformer.

I used the flyback transformer/line output transformer out of an old CRT TV (Not the flat type).

Bozz_Lucre3 years ago
which flyback transformer u have used for it?
Alex1M6 (author)  Bozz_Lucre3 years ago
This is mine still mounted in the TV mainboard;

Any will work though.
DSC_8562 - Copy.JPG
Alex1M6 (author)  Bozz_Lucre3 years ago

Any flyback transformer will work fine for this, I just used one out of an old TV and wrapped 8 turns for a primary coil on to the core. One out of a computer monitor will also work fine.