2n3055 flyback transformer driver for beginners


This instructable will show you how to make a cheap and simple driver circuit in order to get high voltage arcs out of a component called a flyback transformer.

A flyback transformer, sometimes called a line output transformer are used in older 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 the TV manufacturers use to power other parts of the TV, so they are usually customised by the manufacturers.

For the high voltage experimenter they are used to make high voltage arcs, which is what this instructable will show you how to do with just a few simple electronic components.

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


I am in no way responsible if you mess up with this circuit. If you mess up you have no one to blame but yourself.

What you will need:

1x Flyback transformer

1x 2n3055 transistor + heatsink

1x 220 ohm 5 watt resistor

1x 22 ohm 5 watt resistor
(Note: The resistor values do not have to be exact. Say if you had a 33 ohm and a 200 ohm resistor they would still work fine for this circuit).

Some enamelled magnet wire, single core bell wire also works well too for the primary and feedback coils.

A fast diode. Although this is not needed for the circuit to work, it protects the transistor from back emf spikes and can help prolong the life of the circuit. I just used the one I found on the TV board but the UF4007 is an easy one to get hold of in electronic stores if you need to buy one.

+Some way of connecting the components
such as alligator clipped cables or wire and solder.

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Alex1M6 (author) 2 years ago
Skip to 0:44 in this video to see some arcs.

Magnetron2 months ago
I built this twise and it did not work why?? Tanx for upgrading the circuit
Alex1M6 (author)  Magnetron1 month ago

I would start with reversing the connections to one of the coils and listening for any sounds of oscillating, which will sound like a high pitch squeal. Did you scrape enough enamel off of the end of the coils to make a good solid connection?

What sort of power supply are you using?

yes i did scrap of enough enamel and i use a 12v alarm bat3 but i think the problem is my resistors i live in SA and they dont look like the ones you used but tnx for reply
todybog1 month ago

Does the wire have to be magnetic or can i use wire from one of the transformers on the circuit board i have. it seems to be the correct gauge.

Alex1M6 (author)  todybog1 month ago
Any wire will work fine.
todybog Alex1M61 month ago
ok thanks. also i set up a 50 ohm 10 w instead of 22ohm. the others i have lined up to form 200ohm. not 220. but 10 watts each. that okay too?
Alex1M6 (author)  todybog1 month ago

Substituting the 220 ohm resistor for a 200 ohm will be fine but at the expense of slightly more power being wasted as heat. But using 50 ohms in place of the 22 ohm resistor will reduce the final output voltage by quite a bit, worst case the circuit will fail to oscillate.

If you can get hold of another resistor of around 30 ohms 2 watts, place it in parallel with the your current 50 ohm it will work much better and still allow you to use the resistors you already have.

Like in the schematic below:

todybog1 month ago

can i put a 10W 1ohm resistor before the others resistors which are only 1/2 w but the correct amount of ohms?

Alex1M6 (author)  todybog1 month ago

That will not work sorry. The 1 ohm 10 watt resistors will stay cool whilst the 1/2 watt ones will burn up.

ya but it might fry

yea i know. i got two 100ohm 10 w and one 50ohm 10w instead
candrewneal2 months ago

Great tutorial I made mine and it works great! I have a question though. How did you attach the collector wire to the transistor when the heat sink was on? I've tried it on mine but the circuit shorts out when connecting to the bolt and doesn't work. Any suggestions?

Alex1M6 (author)  candrewneal1 month ago

Thanks! That is a good question.

I used a small ring terminal that was threaded over one of the heatsink screws and connected to the circuit board with a small piece of wire. You can get these at any automotive store for pennies/cents.

Make sure that the transistors emitter and base legs are not touching the heatsink when you tighten it down. You can get little securing plates that attach to the back of the transistor and prevent shorts, but you could probably get away with using scrap piece's of wire insulation places over the base and emmiter legs near the transitors body.

There is a good articale on this here

Cormaxzyz5 months ago
I just built this circuit and it works great. So far it only produces fairly short arcs, but I haven't fiddled with the number of turns in the primary at all yet. Thanks for posting this!
UPDATE: The problem was that the battery was almost dead, hence the short arcs. Interestingly enough, I found that the diode heats up a lot, warranting its own heatsink (and even that isn't always enough). Do you know why this might happen?
Alex1M6 (author)  Cormaxzyz1 month ago

Glad you got it working. The diode will get quite warm as it bypasses negative going spikes caused by the LC action of the primary coil and tank capacitor.

If it is heating too much you can use something like a UF5408 instead which is the 3 amp version and will stay much cooler.

Do you wonder to know at which frequency is the output of this circuit at? About 50Hz - 60Hz?
Alex1M6 (author)  shostakovichteddy1 month ago

The one I built oscillates at around 20kHz which drops when into the audible range when drawing an arc (below 17kHz). Any 50/60hz sound will be caused by ripple from an unregulated power supply, add a large smoothing capacitor of around 6800uF across the supply rails to reduce this.

millerair4 months ago
Yes Hailing,
I have an Viore TV with a faulty flyback, the flyback got misplaced can u help me with getting back that flyback number so i can purchase the flayback. Thanks

Model No.CFT27V20
Chassis No. CH-16CD
Hello Alex1M6,
I followed your instructable and made a great one :). One thing that I am wondering is the output of the driver. Is it AC or DC, what is it voltage, amp, frequency? Once I tried to measure it by a multimeter and the multimeter died :(
Bradster970078 months ago
If I put more coils on the primary would it increase output voltage? What about the feedback?
Is thinner or thicker gauge wire better for bigger arcs?

~ Brad
Alex1M6 (author)  Bradster970078 months ago

I found different flyback transformers to react differently. Some worked better with more turns whilst others did not, so experimentation is needed here.

It is more than just turns ratio that determines the size of the arc in this driver, the frequency that this self oscillating driver oscillates at will play a part. There will be a "sweet spot" that produces the biggest arcs, but at the expense of more power draw and transistor heat (mostly, but that is a whole different issue).

Adding turns will increase the inductance of the winding and thus decrease the running frequency.

Generally thicker wire is preferable but anything larger than 20-18SWG is over kill for this.

Bradster970078 months ago
Hi Alex,

As requested I have posted some pictures to help us both out :)

The cables aren't coloured right for the polarities and the wires with blue tape is the primary coil. I am using a 2n3055 and the same heatsink as you, coincidentally. No wires are shorting to the heatsink or others.
Any questions, ask me :)

Alex1M6 (author)  Bradster970078 months ago
Hi thanks for uploading the photos.

From the photos it looks like you have gotten the resistors mixed up. The 220 ohm should be installed where you currently have the 22 ohm, and the 22 ohm should be where you currently have the 220 ohm.

Try swapping them around and see if it works.
I also have a 12V lead acid battery that is 12Ah to use, thanks to my gramps, and my gokart starter motor hehe

breed158 months ago
I have built one of these but there is no high pitched noise. I have tried 2 transistors and swapped the primary and feedback coils' polarity and did everything on your troubleshooting page but nothing is making a noise or outputing any arcs. I am using a PP3 battery just temporerily until it works but do you think if I used a 18v cordless drill battery it will work?

leviterande9 months ago
mine only puts 0.8 inch or 2cm arcs.. what is the length of your arcs? at what voltage?
Alex1M6 (author)  leviterande9 months ago
Depends on the transformer used, my best one put out around 1 inch arc with 12v input (drawing just under 2 amps). Where as another one I have will only do around 1cm.

Try experimenting with using different numbers of primary and feedback turns.
aha I see so it depends on the transformers, I thought all pc crt were the same if they looked the same.. oh well... I have bought a 28" tv to butcher it anyways
Alex1M6 (author)  leviterande9 months ago
If you increased the value of the upper resistor to something like 470 ohm then you could increase the supply voltage to 18v and it might give you some extra grunt to the arc.
hmm gonna try that . I have found that 5 turns primary is what gives me the 1 inch sparks. I see most people use high prim turns.. like 10 and above, if I do that the sparks get very dwarfed, what was your prim turns?
Nico N.11 months ago
Hello. I did this the exact way you said. I am using a 33 ohm and a 220 ohm wirewound flame-proof resistor. I have wound 31 AWG magnet wire at 11 and 7 turns. I am using alligator clips temporarily. I am using a computer charger that supplies 15-24 volts (variable) at 70 watts (that equals 4.6 amps at 15 volts) I am getting nothing and no whistling. I have switched the coils in every possible combination too - nothing. I thought maybe the circuitry inside the charger was not letting the circuit work so I tried 8 AA batteries. Nothing. I am using a 2n3055 transistor temporarily while I wait tor my MJE13009 transistor to come. I am thinking it is the transistor, my coils or the flyback itself. Can you please help? I have made power sources before and I do no understand how this one is not working. Thanks so much. :)
Alex1M6 (author)  Nico N.11 months ago

Try checking for continuity between the coils and rest of the circuit as with magnet wire it is sometimes hard to get a good connection.
Nico N. Alex1M610 months ago
Thanks a lot. I just got my MJE13009 transistors today and it works great. Turns out it was just the 2n3055 transistor. Maybe I burnt it out it or maybe it just dosen't work with my circuit. Anyways thanks a lot for your support. I am so glad I finally got it working even though I don't use it for anything besides entertainment.
were did you get the coil does it have three plastic screws on the side if you are having trouble with striping the magnet wire do it with lighter or torch
mopuccino11 months ago
hey alex ,just wondering ,do you know what is the voltage and amps of the output of this device?(using 12v input) does it work with 9v?(square battery?)
dmytro50911 months ago
Are there any other resistors I can use for this driver?
Alex1M6 (author)  dmytro50911 months ago
Why what sort of resistors do you have?
dmytro509 Alex1M611 months ago
I have the same value resistors that are required in this build. They're just rated at higher wattages. Like I have a 20 ohm 20 watt resistor.

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