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:

Step 1 Requirements

- soldering iron with solder
- a PCB
- a power supply (DC adapter 12V to 20V)
- a heatsink (the size of the heatsink depends on the flyback and on the type of MOSFET, you'll have to experiment)
- a MOSFET (I used an IRFB17N50L because they're awesome)
- wire for making connections at the bottom of the PCB
- 2x potentiometer 100kohm
- 2x resistor 260ohm 250mW
- 2x resistor 1kohm 250mW
- 1x resistor 4k7ohm 250mW for the LED (high resistance so that we can also use greater power supplies)
- 2x capacitor 3.3nF polyester film or something close to that
- 2x NPN transistor (regular transistor)
- a small pushbutton (not required)
- a flyback transformer (not required)
- a FAN connector for inserting the MOSFET (not required, you may solder it directly on your PCB)

The picture above here shows how the components look like.

Comments

[miar56]

Will this work using a MTW32N20E mosfet. It's a N channel but seems to have an internal Zener across the source and the gate?

[Electorials]

This mosfet is good.
The diode protects the mosfet, most mosfets have one there.

[geckomage]

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

[Electorials]

ok ;)

[UATradition]

Got it working on led's and DC motors but not for my flyback ..... however - Once I turn up the on time pot all the way the led on board gets dim and the flyback makes a click - ? Ant idea of what this could be ? And it doesn't matter where the other pot is unless it's all the way up too - that's the only time the led on board stays bright.

[Electorials]

I think your supply can't deliver enough current.

[geckomage]

hello my friend, how have you been? :P will this one work decently compared to the ultimate one? because i have the parts for this but not for the ultimate one :P nice bug zapper btw! also i noticed you have a fairly big coil on your flyback. for my flyback i used 14 awg wire and 6 turns xD

[Electorials]

Hi there, I'm fine ^^ thanks

I have more turns on the flyback's primary because my power supply can only deliver 3A.

thanks for the bug zapper haha :D

And yes, this one also works fine ;) I still use it.

[geckomage]

ohh.. this is right o.o i might have to adjust that for when i have to run this thing without two robot batteries xD poodles. i might try to find a good wall power supply that can deliver like 10 amps or w/e is needed. :3 my lil circuit is working properly all bread boarded up. only thing missing on the circuit is the filter caps, and the flyback/mosfets. (the signal goin to the mosfets thats spose to be flipped in reverse with a GDT is workin aight though throwin out 24 v like its spose to :D) soo when i actually make this thing, im hoping it will work! :D what you workin on next?

[Electorials]

filter caps? there are no filter caps on this circuit.
I'm not really working at something right now, I'm quite busy :(

[UATradition]

Will different capacitors work with this ? And also what about a capacitor bank ?

[UATradition]

Also the materials say 2 x 260ohm resistors but the schematic says 560 ??? I'm going to go with the 260 right now ! Maybe you'll catch me before it's too late !! HA !

[Electorials]

Oh no, it's 560ohm, sorry.

and you'll have to use two the same capacitors.

[UATradition]

(removed by author or community request)

[budhaztm]

I need some assistence on the mosfet. im pretty confident i wired the two smaller transistors in correctly but im not sure how to wire the big one

[Electorials]

Most MOSFETs will have their connections in this order, from left to right, when holding the front of the MOSFET towards you:
G, D, S

I can't tell you for sure that this will be exactly the same on your mosfet, so you should look up the connections in the datasheet of your mosfet.

If you can't find the datasheet for it, please send me the printed numbers from on your MOSFET and then I'll look it up.

[budhaztm]

ok. so lets say i find the gate,drain and source connections for my mosfet. I cant ynderstand the diagram where it has the mosfet. this is my first real circuit and i needs help. thanks by the way

[Electorials]

The mosfet can be found in the diagram in the total right.
(It sais 'MOSFET' above it ??)

Or do you mean the print board? because I think you did find it on the diagram (schematic).

on the print board, it is connected into the PC FAN socket (the white plug)
and it's mounted on the big black cooling plate (heat sink).

[budhaztm]

i dont quite understand the part where the mosfet is on the diagram, theres too many lines

[Electorials]

Oh, that is what you mean.

The weird lines are just the symbol of the mosfet.

The three wires leaving the MOSFET symbol are the three pins of the mosfet itself.

Just don't mind the weird symbol, there is nothing you need to connect there, it's all internally in your mosfet already.

[Hav0c]

do you have to use a MOSFET or can you use a power transistor

[Electorials]

I didn't try it yet with power transistors, but if they also have fast switching times and if they can carry the current, then it shouldn't be a problem.

[budhaztm]

Ok, i took apart two computer monitors to get parts for my science project and i need to construct this amazing device.
I have a handful of what i think are MOSFETS, or transistors. THey all have three prongs and the numbers are as goes: IRFS640A, FS14SM16A and C54119K (this last one says its toshiba). I was curious if i could use one of these instead of buying a mosfet.
Thanks for your help.

[Electorials]

IRFS640A: perfect for this application
FS14SM16A: also perfect
C54119K: I have no idea what that is

You definitely don't need to buy a MOSFET. Both the first and second are Power MOSFET's and are perfect for this application.

Sorry for the late reply.

[Alex1M6]

I *think* C54119K is a horizontal output transistor.

[yellowdart31]

This is awesome. Every other PWM I've seen is 555 driven (I'm new to electronics). I have a few questions though: What is the frequency range of this device? (ie. range of times for high and low intervals)? Is there a formula for predicting the time of the high and low intervals based on the setting of the potentiometers? Would you explain or provide a link to an explanation of the theory of operation of this circuit? Thanks!

[spark light]

http://www.falstad.com/circuit/e-multivib-a.html

http://www.davidbridgen.com/astable.htm

[yellowdart31]

THANKS!! That's even more than I asked for... an actual simulator!!! Wow! ... That site has a LOT of other simulators too... aaannd bookmarked!

[Alex1M6]

Hi what capacitance are those 3.3 "m" capacitors? do you mean nF, uF or mF ?

Thanks.

[Electorials]

it's 3,3nF (nano Farad)


This is printed on the capacitor:

332J
2ASIC

I'm pretty sure that means 3300pF ;)

[Alex1M6]

Thanks,

One more thing what npn transistors did you use and does the MOSFET get hot?

[Electorials]

The mosfet does get hot, you really need a heatsink.

The transistors I used are 'F422' but it doesn't really matter which you take.

[Alex1M6]

Well done on this circuit.

I am going to give this a try as all of my 555 based drivers keep dieing.

[Electorials]

Thanks, good luck ;)

[TheBlackBird]

Hello.
Very nice instructable, i need to drive a SSC-P7 LED at max brightness and i've been looking everywhere for an easy to build driver and i found yours.
So can this controller be used to drive a power led? and how much current can the mosfet handle?
I'm going to build it anyway (because it's great) but i ask about the led because i don't know if it could destroy it or not.

Thank You!

[Electorials]

Hi,

The mosfet I'm using can hande 16A continues drain current, but it really depends on what mosfet you'll use.

For the power LED: If your power LED is rated at, for example, 4V, then you'll have to use a power supply rated also at 4V.

If the voltage of your power supply is larger, you'll kill the LED when the ON-time of the PWM is maximum and the OFF-time is minimum.

And an answer to your question: Yes, using an LED on a PWM controller is no problem. It'll work just like you want to.

Greetings,
Electorials

[slipknot rules]

Nice 'ible! Have been using the 555 timer + MOSFET method for a while but am keen to give this one a try! Cheers!

[Electorials]

thanks ;)

[diykiwibloke]

Thanks for clarifying *Electorials* and *domints*. Now it makes sense. I enjoyed your video Electorials. I could tell which was your favorite part in your demo. I too used to love creating sparks in a past life, built tesla coils and so on :) I'm only just recently getting into electronics again.

Again, thanks for posting this 'ible.

[domints]

No problem ;)