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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Step 1: Mount the transistor onto the heat sink

Picture of Mount the transistor onto the heat sink

Mount the transistor onto the heat sink. The heatsink is important as the transistor gets hot. I just bought the cheapest heatsink maplin sell. The 2n3055 is a TO-3 case style.

You can use an insulator pad if you want but I just used a small amount of old thermal grease I had lying around. To mount the transistor to the heatsink I just used some spare screws and nuts I had in the garage.

Make sure that the transistor pins do not physically touch the heatsink and it is screwed in securely.

Q: Can I use a different transistor?
A: Yes you can, as long as the transistor has similar specs to the 2n3055 or better.

Q: Can I use a PNP transistor?
A: Yes, but you will have to reverse the collector and emitter connections in order for it to work. It will also need to have similar or higher specs as the 2n3055 transistor.

Q: Is the heatsink really needed?
A: Yes, if you are wanting to use this circuit for more than a few seconds the heatsink is vital as the transistor will get hot fast.

Q: Can I use a MOSFET?
A: No, a MOSFET will not work for this circuit.

Step 2: Preparing the flyback

Using some enamelled magnet wire wind two coils around the core of the transformer in the SAME DIRECTION.

11 turns primary and 7 turns feedback is a good starting point but you can try more or less windings to see what gives the best results.

Using a sharp knife carefully scrape away the enamel coating from the very ends of the magent wire.

Once you have wound the coils and removed the enamel at the ends of the wire check for continuity using a multimeter, doing this can save you lots of bother later on!

You do not need to worry about finding the HV return pin yet.

Step 3: Putting the circuit together

Connect all of the components together as shown in the images above.

In the graphical diagram, the red coil is the primary coil with one end connecting to the positive "+" of the power supply/battery, the other end connects to the transistors collector which is actually the metal casing of the transistor itself.

The green coil is the feedback coil with one end connecting to the middle point of the two resistors, and the other to the transistors base (looking at the transistors underside this is the pin on the left).

If you have some alligator clipped wires then you can use these for temporary connections whilst you familiarise yourself with the circuit.

Step 4: Check everything

Picture of Check everything

Check to make sure that your circuit is connected up correctly.

You can use a multimeter set to measure continuity or resistance to make sure that everything is making good electrical contact.

Step 5: Safety first!

Picture of Safety first!
When drawing arcs...

I strongly urge you to make a "chicken stick", which is a 1 foot long minimum insulating stick of some sort. PVC pipe is very good for this. Wood is fine too but when damp it becomes a good conductor at high voltages.

Secure an electrode of some sort onto the end of it, sharp pointed nails work well and will give slightly larger arcs than rounded electrodes. You can then attach a wire of some sort to the chicken stick electrode the other end will be attached to the HV return pin on the flyback transformer.

Other safety concerns

Including the obvious risk of electric shock another thing to take note of is that the arc is VERY hot and can easily set to fire to anything that it touches. Even the cable insulation will burn if you draw the arc onto it.

So if you insist on burning pieces of paper or other objects take that into account and have some way of putting the fire out.
  • You should never touch the high voltage wire or any of the flyback base pins when the circuit is turned on.
  • Make sure that you can easily disconnect the power to the circuit.
  • Do not use this circuit on an unsuitable surface such as a metal table or flammable surface.
  • The transistor heat-sink can get hot so watch out not to burn your hand on it.
  • Keep any high voltage cables away from other parts of the circuit and low voltage cables.
  • Use common sense.
  • Keep pets away. As well as the risk of shocking your pet from the sparks many household pets like to chew things such as wires.
Following those basic safety steps you will be fine.


I am no way responsible if you mess up with this circuit.

Step 6: Powering the circuit

Picture of Powering the circuit
To power the circuit you can use any 12V source that can supply a minimum of 2 amps, as a rule.

AA battery's in series can be used but they will not last long and the arc length will get smaller and smaller as they drain.

x2 6v lantern battery's can be used and will power this circuit nicely for a decent amount of time before the arcs start getting smaller.

A 12v lead acid battery is a very good way of powering this circuit and what I personally use.

A 12V power supply can also be used providing that it can deliver 2 or more amps.

I do NOT recommended 9v /PP3 battery's as they will not last long at all and even when new are unable to provide the current needed for a decent sized arc.

Step 7: Finding the high voltage return

To find the high voltage return first attach your chicken stick to the high voltage out (the big thick red wire) and turn the circuit on. You should hear a high pitch noise. If you don't here this noise then go to the trouble shooting page at the end.

Bring the chicken stick close to the base pins on the flyback and go past each one individually. Some of them may give a slight spark but one of them should give a solid constant HV arc, this will be your HV return pin. You should now disconnect your chicken stick from the HV out and connect it to the HV return pin instead.

In the image's above are some arcs produced by my 2n3055 driver and some different flyback transformers, most flybacks will only give around a 1-2cm arc on 12V input and upping the input voltage only increases heating on the transistor in my experience.

Have fun and remember not to run this circuit for periods longer than 1 minute as the transistor gets hot fast.

Step 9: So how does it operate?

Note: this is what I think is happening with this circuit, if someone with more knowledge could correct me in the comments I would be more than grateful to know!

When you first apply power to the circuit a small amount of current starts flowing through the voltage divider resistors and feedback coil and into the transistor base, as part of this current path is wound around the ferrite core (feedback coil) it stores some inductive energy in the core.

As current is now flowing through the base the transistor is now forward bias which turns it on.

Current then starts flowing through the primary coil and into the transistors collector and out of the emitter (conventional current flow BTW). Current will keep building up in the primary coil until core saturation occurs. This takes the voltage of the feedback coil down to almost zero and the transistor falls back into its linear region.

As the transistor turns off, the magnetic field in the feedback coil collapses which creates both a high voltage pulse in the secondary coil and a small voltage boost in the primary coil (this is why the transistor has to be a high voltage transistor).

As the induced current is in the opposite direction to the supply current i am thinking this serves a current limiting action to the circuit, which might explain why it only seems to draw 2 amps max. If this was a non-inductive load then the transistor turning on would effectively be shorting the power supply right now.

As the transistor turns off the magnetic energy stored in the core from the primary coil rapidly collapses giving an even higher voltage pulse on the high voltage secondary coil.

The process repeats its self thousands of times per second.

Please correct me in the comments if I got any of this wrong!

Step 10: Troubleshooting


Ok so you have made the circuit and it either does not work or it does not work very well.

  • If nothing happens and you cannot hear any high pitched noise from the flyback transformer then try reversing the connections to the primary and feedback coils, if you still get nothing try just changing the connections on one of the coils. Usually this resolves that issue.

  • If you have tried that and still nothing then you should check the circuit and make sure all connections are secure and nothing is shorting out. Sometimes people will forget to remove enough enamel on the magnet wire primary and feedback coils and there will be no electrical connection being made.

  • If it works but the arc is small try reversing both the primary and feedback coil connections. Remember that around 2cm is the maximum arc length you are going to get out of this driver, and 1cm may also be the maximum on some flybacks.
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Alex1M6 (author) 2 years ago
Skip to 0:44 in this video to see some arcs.

HighCurrent17 days ago

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

Alex1M6 (author)  HighCurrent14 days 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)  mopuccino14 days 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.

Sarthak311 month 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.

Sarthak312 months ago
Alex1M6 (author)  Sarthak312 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 Alex1M62 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)  Sarthak311 month 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

candrewneal5 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)  candrewneal4 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.

tezza122 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)  tezza122 months ago

Hi tezza,

Which capacitor are you referring to?

Magnetron5 months ago
I built this twise and it did not work why?? Tanx for upgrading the circuit
Alex1M6 (author)  Magnetron4 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 Alex1M64 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
todybog4 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)  todybog4 months ago
Any wire will work fine.
todybog Alex1M64 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)  todybog4 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:

todybog4 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)  todybog4 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 todybog4 months ago

ya but it might fry

todybog my wookie4 months ago
yea i know. i got two 100ohm 10 w and one 50ohm 10w instead
Cormaxzyz8 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)  Cormaxzyz4 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)  shostakovichteddy4 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.

millerair7 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 :(
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