2n3055 flyback transformer driver for beginners

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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) 3 years ago
Skip to 0:44 in this video to see some arcs.

great instructable! I'd like to add that after powering off, it's a good idea to short the hv output to each of the bottom pins of the flyback, because at high voltages, transformers with multiple coils can act as a capacitor and store a charge. while it's not enough to hurt you, it can startle the crap out of you, causing you to Yank your hand back, cutting it on a piece of sharp metal that happened to be on your work bench from another project....but of course that's never happened to me. (blushing ) lol
aryh14 days ago

help, I had previously tried this driver and it worked, after I run for a few minutes my transistor popping and I replaced it with the same transistor but it does not work, the transistor begins to heat up and no spark

thank you,sorry for bad english

GaryK52 months ago

i did this circuit a few times and failed. I did it sloppy the first time so i took my time and put it all on a wooden board just like in the diagram and it worked great. Thank you alex1m6. I always wanted a high power source and thanks to you it happened. I am just thrilled to see it work. It was worth building. Thanks a million my man.

Mehulk202 months ago

what happen if i use 2 or more transistor or greater then 2n3055 and more resistors of same value that you suggested us and a more powerful it sufficient to drive out 30kv. if not then can you please suggest us what to do for driving 30kv output from a fly back transformer of a monitor.

one more question ???

can i use transistors ,diodes ,capacitors ,resistors etc from my monitors circuit board.

PedroR82 months ago

Do I must use the resistors, or this circuit (2n3055 flyback driver) works without them?

PedroR8 PedroR82 months ago

What are the resistors for?

naga venu3 months ago

I have one flyback transformer which has only 3 bottom terminals and one output bulk red wire. How much voltage it can give ? I tired it with 9V and 12V DC but can't get output voltage.

Thanks in advance.

ann.bragonje3 months ago

I am trying to help my son with his science project which includes making the arc and then comparing different shaped electrodes. We are having a problem finding the flyback transformer. Is there another transformer that would work?

enelson85 months ago
Hey! I love this and actually got it to work! But how much amps or volts would I need for a like 1.5 - 2 inch jump? This is using 9-12v with 2000mA
14, 9:04 AM.jpg
ualbuquerque6 months ago

Cool! Simple and efficient

JonS18 months 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?

But doiding would stop hv feedback and that means you wont burn as many transistors just take a fast speed diode and conect it from the emitor to the collector make sure its going in that direction.
Srry about that
Well yes dioding would stop hv feedback to th
please help me ! my arcs are smaller than 1 cm, I want to increase arc length
Alex1M6 (author)   hemant solanki7 months ago
Have you tried reversing the connections to the primary and feedback coils? As this circuit will only give the best arcs when the coils are the right way around, this is caused by the internal diode built into the flybacks high voltage winding.

If swapping them around just makes the arcs smaller then experiment with the number of turns, I have a few flybacks that need lots of turns in order to give much of an arc.

On the driver reducing the 22 ohm resistor usually gives instant longer arcs, try something like 12-15 ohms there. A 33 ohm 2 watt in parallel with the current 22 ohm resistor will suffice.

What sort of power supply are you using to power the circuit? It should be able to supply 3 amps at 12 volts.
I have tried reversing connection to the primary and feedback coil, but it reduces arc length.I an using a DC supply at around 9 volt and 1.5 amps.

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

Alex1M6 (author)  sabah.malik.5607 months ago
Which part of this circuit do you need help with?

Google for "blocking oscillator", which is what this circuit is.

When power is first applied to the circuit the transistor is off. Current flows through the resistors which form a potential divider and into the base of the transistor via the feedback winding. This turns the transistor on.

The transistor turns on and current begins to flow through the primary coil, as this happens an EMF is induced into the secondary winding but no current can flow there since the flybacks internal diode blocks it.

As the current in the primary ramps up it also induces an EMF on the feedback winding which opposes the EMF from the potential divider, turning the transistor off.

When the transistor turns off the current in the primary coil is suddenly interrupted and large negative voltage spike appears across the primary, a stepped up voltage also appears on the output of the flybacks secondary coil.

But now there is nothing to keep the transistor off so the cycle repeats itself over and over.

Hope I managed to explain that ok.
HighCurrent9 months ago

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

Alex1M6 (author)  HighCurrent9 months 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)  mopuccino9 months 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.

Sarthak3110 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.

Sarthak3111 months ago
Alex1M6 (author)  Sarthak3111 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 Alex1M611 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)  Sarthak3110 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 Alex1M610 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)  Sarthak3110 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

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 year 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)  candrewneal10 months ago

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

tezza1210 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)  tezza1210 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.

tezza1211 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

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