Picture of Simple PWM Flyback driver tutorial
Hi there,

This is an instructable for making your own PWM (Pulse Width Modulated) flyback driver!
The design is relatively simple and easy to make if you have basic electronic skills.
In fact, you don't even have to know how a transistor or a MOSFET works to make this. You only have to follow the instructions.

What the PWM driver does:
The driver is fed by a 12V power supply (a regular DC adapter). This DC voltage is chopped into pieces by our MOSFET because it rapidly switches the 12V on and off. This switching is controllable by two potentiometers. One for the ON-time and one for the OFF-time.
If the ON-time and the OFF-time are equal, the output voltage will be 6V.
If the ON-time is larger then the OFF-time, the output voltage will be between 6V and 12V
If the ON-time is smaller then the OFF-time, the output voltage will be between 0V and 6V.
So with this feature, we can control the average voltage that our primary Flyback coil gets. This will change the output voltage.

When we make sure both potentiometers have the same resistance value, we'll create a block-wave signal that has the same ON- as OFF-time. Decreasing the resistance (of both potentiometers, at the same time) will increase the frequency of the output signal. Increasing the resistance will decrease the frequency.

We now have controllable ON- and OFF-time, and controllable frequency, so this driver is perfect for Any flyback transformer! (Each flyback transformer works better on another frequency).

The operating frequency of the flyback transformer goes somewhere from 15kHz to 50kHz. My flybacks operate best at 20kHz.

(oh, and the power supply doesn't need to be exactly 12V. You can also use a 30V supply or something a little lower then 12V).

Preview video of the PWM driver:

Remove these adsRemove these ads by Signing Up
1-40 of 101Next »
dillonxti1 month ago
this will work better for driving a flyback
dillonxti1 month ago
will it work with all 5 resistors are 1000

timthet0olman7 months ago

parts list says 2x 260 ohm pic shows 2x 560 ohm

dillonxti1 year ago

neat project shabby camera work on the video

geckomage3 years ago
i was referring to my plasma speaker ;D it has filter caps ^__^

Could you help me out??
I'm trying to make a plasma speaker but i can't seem to manage it to work.
Which schematic did you use?
Please respond as soon as you can!

Electorials (author)  geckomage3 years ago
ok ;)
mszponar1 year ago
I need to know something, is the circuit suppose to make a square wave and so if I hooked up an LED then the LED should flash depending on the pots right?
mszponar1 year ago
so reading some comments I've figured out maybe I dont have enough current going into my flyback, so if thats the problem how can I increase my current? can I do this by attaching bigger capacitors?
mszponar1 year ago
Great simple circuit and but one thing I dont understand fully is how to exactly attach this to the flyback driver. I got it working and everything's good, and maybe this a stupid question I just cant figure out how to connect it to the flyback lol.
interesting, I thought you could only control pwm and freq. with 555 or similar ..
A 555 has a circuit inside it, you just can't see it. ICs aren't magic.
I wish I could upvote your reply...
SirCheez1 year ago
Runaway Pancake on the Arduino forum came up with a great solution to the button problem. Source
When I increase the duty cycle at the same frequency the voltage of the secondary drops instead.. hmm is that because I am using a transistor instead of a MOSFET?
Electorials (author)  leviterande1 year ago
It is normal that the secondary voltage increases when you increase the duty-cycle, up to a certain point where it stops increasing.
This usually happens around 40-50% duty cycle.

The reason why is because the magnetic field inside the core of the transformer saturates.

However it's kind of odd that it actually Decreases for you, instead of just stopping to increase. Probably because it is not an ordinary transformer. I am not really familiar with HF transformers. I do know that the same thing as you experience, also happens with flyback transformers. The output voltage will also decrease after a certain duty-cycle has been reached.

It's probably not because you use a regular transistor, as a MOSFET is also a transistor.

I wouldn't worrie; this is probably just typical behavior of your transformer.
Thanx a ton for your help!. The HF transformer is just a typical small ferrite core with many pins used in many CRTs. like this one : , my actually duty cycle test was from 58% to 80% at same 25khz freq. The voltage of secondary dropped from 35v to 0.1 V... I cant decrease to less than 50% duty anyway.
Hi, First of all your driver and tutorial is the a clear and fulfilling one! you seem to be the guy I have been looking for to answer my question killing me for ages now. I don't know where to contact you, but anyway I want to charge/discharge around say- a 1nF capacitor with this flyback, is it possible? will the cap be fully charged and discharged each cycle of the frequency that we choose? Your help is extremely appreciated.
Electorials (author)  leviterande1 year ago

I'm not really sure if I understand the question.
So you want to charge a capacitor with high voltage?

For the frequency, I don't know how to calculate how fast the capacitor will charge because the output current is unknown.

It will just be trial and error :P

donmatos2 years ago
se admite questões estúpidas, as ignorantes não serão problema, creio. apesar de leigo em eletrônica, sou fascinado pelo tema. tenho tentado executar alguns dos seus vários instructables, obtendo exito em boa parte dessas tentativas. sou hobbysta interessado  na aplicação de diversos materiais, e não num ofício específico. minhas pcbs de sucata não poderiam ser transportadas num carro pequeno... eu olho pra elas, e elas pra mim... e me perguntam: e aí? ... flybacks despencam das prateleiras... então, por favor me diz (caso tenha algum tempo pra responder a estas abobrinhas): em que projetos eu poderia utilizar esses monstrinhos. já te agradeço, apenas por ter lido até aqui,obrigado.
Electorials (author)  donmatos2 years ago
It is quite difficult to understand what you are saying. Using google translate, it looks like you are asking how you can use courgettes; zucchini, in a project. But I think you're talking about Legrand Zucchini High Power devices?

Could you explain me more? I don't quite understand :/
Primeiro, muito obrigado por responder meu comentário; e, segundo, acho que exagerei com vocábulos do dialeto local, e mesmo assim vc ainda conseguiu entender. Parabéns pela perspicácia. A dúvida: eu preciso saber sobre as aplicações das fontes de alta tensão: ou seja, em quais dispositivos (aparelhos) eletro-eletrônicos elas podem ser utilizadas? Em resumo, qual a utilidade delas (fontes HV) nas tarefas do nosso dia-a-dia? Só alguns exemplos. Obrigado, mesmo.
Electorials (author)  donmatos2 years ago
É muito difícil entender o que você está dizendo. Usando Traduz Google, parece que você está perguntando como você pode usar as curgetes; abobrinha, em um projeto. Mas eu acho que você está falando Zucchini Legrand dispositivos de alta potência?

Poderia explicar-me mais? Eu não entendo muito bem :/
Ugh. Like on any electronics project i do, it isn't working for me. I triple checked it. I made sure all the connections were good. Still nothing. When i attach a 12v battery, the light turns on, but past that nothing. When i attach a voltmeter to the output, i get ~50mv (megavolt) out of it, which is probably the caps. I bought all the parts from digikey, all to your specifications. I still cant figure it out. help me maybe?
Electorials (author)  RocketPenguin2 years ago
Hmm that'e weird,
Can you measure Vgs and Vds (gate-source and drain-source voltage) of the mosfet while it's running?
The gat source is only .013 volt O.o And the Drain is 0 volt... Thats not good is it...
Electorials (author)  RocketPenguin2 years ago
ok, and did you measure this while a load was connected on the output? or was the output just an open connection?
Open. what type of load would you recommend to put on it to measure the voltage? Anything i usually put on it, whether it be a motor or a flyback, noting works.
Electorials (author)  RocketPenguin1 year ago
hmm can you also do a measurement with a closed output? Preferably a resistive load. (so not motor/flyback, but a resistor, light bulb, ...)
I attached a neon bulb to it... Source gate i got .007 volt, and drain i got .004 volt. I will be borrowing a scope soon, and will measure it with that to be more accurate.
Electorials (author)  RocketPenguin1 year ago
hmm the two transistors are just not working :/
Can you measure the base-emittor and collector-emittor voltage on both transistors?
You don't really need a scope, the readings don't need to be more accurate, but from the moment the circuit works, a scope would be really nice to visualize what is going on.
Ok, so, attach a load, and do the same thing with both transistors? Everything is new except two resistors and the LED. I don't think i burned out the transistors... When i soldiered it, i used 400F and didn't keep it on for more than a few seconds...
Electorials (author)  RocketPenguin1 year ago
ok, good,
but for measuring at the transistors, no load needs to be attached now :)
For the one of them, between Base and Emitter, 9.48v, and between base and collector 10.22v For the other one between Base and Emitter 10.83v, and Base and collector 12.28v. Maybe i wired them in wrong? I checked on the datasheet, and wired them in according to that.
Electorials (author)  RocketPenguin1 year ago
And did you test by pushing a button like on the schematic? Or shortly jumping that connection with a wire? That might start the oscillator
btw, I'd also need the collector-emittor voltage, not the base-emittor voltage ^^
I have pushed the switch, One of them is .76v the other 1.46v
Any ideas? you seemed to stop replying.
And only .7 volts go into the source...
mgingerich2 years ago
I have an explanation for the need for a pushbutton, if you haven't already figured it out. This circuit is based on an astable multivibrator, which means it oscillates between two states, neither of which is supposed to be stable. However, when the power is interrupted, it sometimes gets "stuck" in one state. The pushbutton forces a capacitor to discharge, starting the oscillation again. I had this problem with a similar noisemaker circuit.
Electorials (author)  mgingerich2 years ago
Indeed ;)
1-40 of 101Next »