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.

help me i have to make a fly back driver circuit as teacher has given us this for project
teach me some thing as i realy dont even know the basics of this circuit
y we mAKE This
help me

JonS110 days ago

I tried this circuit and failed, probably because I am trying to locate the internal primary and feedback coils on the pins. Perhaps I have watched too many youtube vids on the subject and the ones who posted were lucky enough to have found them and hooked them up properly, and I am not so lucky. Why am I frying my transistors? Coils hooked up in reverse? Back HV? Is this all folly, and much easier done by making my own primary/feedback winds on the ferrite? Would dioding the circuit prevent all of this?

HighCurrent1 month ago

My flyback had the HV return pin torn off on accident.any ideas?

Alex1M6 (author)  HighCurrent1 month ago

Has the entire pin come all the way out or has it snapped right at the epoxy potting?

If it is the latter you can chip away at the epoxy and solder a piece of wire into the remainder of the pin. If it has come all the way out then try putting some thick wire in there, if you get a good fit it should make decent contact with the end of the HV winding.

I have attached an image to show you what I mean, click on it to get a full view.

mopuccino1 year 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?)
Alex1M6 (author)  mopuccino1 month ago

1 year late I know...

Out of the flyback you will probably end up with around 10-15kV @ a milliamp or two.

A fresh 9v battery will sort of work for a few minutes, but it will give very weak sparks on the output. A 12v power supply that can deliver a few amps will be much better.

Sarthak312 months ago

I made it with primary 7 turns and feedback 5 turns it was working fine but then i used 37 turns with 25 , 13 ,17 turns but they all gave very small arks and gave a high pitch sound whereas in the first case there were relatively larger arks with no noise.

Can you give the combination for some larger no. of turns and also tell me the cause for this.

Sarthak313 months ago
Alex1M6 (author)  Sarthak313 months ago

Sorry but that is not suitable for this application. It needs to be a 220 ohm and an additional 22 ohm power resistor of 2 watts and above, that is a 220k (kilo-ohm) potentiometer which is too high.

I had a look on that website for a suitable resistor but can't find any listed, are there any other electronics stores that you can purchase from? If so post a link and I'll find the appropriate resistors for you.
Sarthak31 Alex1M63 months ago

Thanks for the reply

can i get one form this site

and earlier i gave you the wrong link it was originally

Alex1M6 (author)  Sarthak312 months ago

Hi Sarthak,

I had a look on onlinetps and although they don't have the exact resistor values, you can use a combination of other values to get the correct one. I've attached an image to show you what I mean complete with part numbers.

I know its not neat but it will work.

Regarding the electroncomponentslink, that is an adjustable resistor (potentiometer) and will get hot and burn out if used with this circuit.

Sarthak31 Alex1M62 months ago

Thanks Man

I think that the diode is upside down as cathode of the diode is connected to positive terminal of the battery(I am not sure)

Alex1M6 (author)  Sarthak312 months ago


How the diode is shown in the diagram is correct (anode to ground, cathode to collector). It is only there to bypass any negative going voltages that may ring over the collector to emitter junction.

Are you not getting any output from the flyback transformer?

How can i check if my flyback transformer is broken

candrewneal6 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)  candrewneal5 months 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

Works great! Thanks for the reply! I'm highly considering building a ZVS driver for my next project. :D

Alex1M6 (author)  candrewneal2 months ago

Your welcome! ZVS drivers are great fun but require lots of current to work well lol.

tezza122 months ago

Regarding the Diode!

I have a 1N4007 Diode & a BY228 Diode would either of these work ok & if so which would be the best option.

Many thanks


Alex1M6 (author)  tezza122 months ago

Hi Tezza,

Anyone of those diodes would work, but a "fast recovery" diode is normally preferred here such as UF4007, BYV26 etc.

This is becuase diodes can actually conduct in reverse for a brief period of time when they suddenly go from forward bias to reverse bias. The switching frequencys and harmonics present in this flyback driver are right at the upper limit for a standard recovery diode (1N4007, BY228 etc).

But out of the two you already have I would just use the 1N4007 since the BY228 is way over rated in terms of breakdown voltage and current, save it for another circuit.

tezza123 months ago

Could someone please advise me where about to place the capacitor & what values it should be. I am new to electronics so any help what be great. Thanks. Tezza

Alex1M6 (author)  tezza123 months ago

Hi tezza,

Which capacitor are you referring to?

Magnetron6 months ago
I built this twise and it did not work why?? Tanx for upgrading the circuit
Alex1M6 (author)  Magnetron5 months 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?

Magnetron Alex1M65 months ago
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
todybog5 months 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)  todybog5 months ago
Any wire will work fine.
todybog Alex1M65 months 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)  todybog5 months 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:

todybog5 months 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)  todybog5 months ago

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

my wookie todybog5 months ago

ya but it might fry

todybog my wookie5 months ago
yea i know. i got two 100ohm 10 w and one 50ohm 10w instead
Cormaxzyz9 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)  Cormaxzyz5 months 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)  shostakovichteddy5 months 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.

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