Re: Flyback problems
Dr. Dark Current, Sat Mar 17 2007, 12:55PM

What I can think of now: how many primary turns do you have? (you should have about 10-15 turns for this supply voltage). Is the flyback's core gapped? Are you powering the 555 from a voltage regulator ("7812")? Is the supply of the 555 well filtered with capacitors? What frequency are you using? (should be around 20Khz) What mosfet are you using? (should have at least 200V rating and on-resistance no higher than about 0.5Ohms (these are just guesses)). And finally, have you tried reversing primary polarity (if you have dc flyback)?
I know these are a lot of things but if any of those is wrong it can decrease performance.

Re: Flyback problems
Munkey, Sat Mar 17 2007, 01:35PM

I have 2 turns on the outside ring bit of the flyback (Im using the morden kind with about a million pins on the bottom)

Sorry but I dont know what you mean by: "Is the flyback's core gapped"

I am providing the 555 with a unregulated 12-13VDC supply which is smoothed with a 2200uF cap.

I dont know what frequency I am using, I dont have a oscilloscope or any freqency measuring equipment.

The MOSFETS I am using are IRF630, they are behaving very weird, sometimes when there is no voltage on the gate it still conducts.

Im not sure if I have a DC flyback but when I reverse the connections on the primary it makes no difference...

Re: Flyback problems
Dr. Dark Current, Sat Mar 17 2007, 02:01PM

Put there some more turns (start with about 15 and then decrease). Have you correctly identified the ground pin on the flyback's base?
This means there is an intentional gap in the core to store energy. If you didn't dismantle your flyback then the core is for sure gapped.
This is normal, since the gate is like a capacitor (it charges up and stays charged).

I have drawn a schematic for you, hope it helps:

Re: Flyback problems
Zum Beispiel, Sat Mar 17 2007, 02:03PM

There are lots of online calculators for 555s...

Two turns on the core is too little, try winding some more and see if that helps.

I really think you should buy a cheap multimeter with frequency & duty cycle measuring capability. You can get cheap ones for around 20€/$. A (good) multimeter is probably the second best thing to having a scope. If you for some reason can't get one, you can take a small speaker and use it to "probe" the output. The tone will give you a rough idea of the frequency (atleast if its less than 20kHz.)

A mosfets gate is basically a (small) capacitor, so if you don't connect it to anything it may still pick up charge and make it conduct.

Really, if you are a complete noob at electronics, I might suggest you build the single 3055 flyback driver. it has only three parts, and it should give you some semi-nice sparks. There are lots of schematics on the net for it, just google "single transistor flyback driver" or something like that.

I hope this helps you.

Re: Flyback problems
Munkey, Sat Mar 17 2007, 02:34PM

Thanks for the circuits. I have just found out that I have blown my third 555 timer so ill buy a new one, then make the 555 and 2N3055 flyback driver circuits.

jmartis: In your circuit on the HV secondary there is a earth symbol, where is that ment to go, earth earth or household earth?

Zb: Ive found a calculator and it is giving out about 3khz oops a bit to low...

Re: Flyback problems
Dr. Dark Current, Sat Mar 17 2007, 02:41PM

mains earth (or if you call it household)
May I ask you one question which I'm not sure about, where you wound your primary? Is it on the exposed ferrite core (the black rectangular thing that is coming from the flyback) or around the plastic flyback case??

Re: Flyback problems
Munkey, Sat Mar 17 2007, 03:10PM

Ah, rignt.

I have just finished winding my primary of 14 turns so I am going to put a link to a picture here:

Re: Flyback problems
Dr. Dark Current, Sat Mar 17 2007, 03:11PM

That looks OK.

Re: Flyback problems
Munkey, Sat Mar 17 2007, 05:05PM

I have made the 555 timer circuit with the IRF630 mosfet and... Nothing, the distance I was trying to spark across was about 2mm. The supply voltage was 15 at 2A.

Re: Flyback problems
Marko, Sat Mar 17 2007, 05:18PM

Unless you have some other cardinal mistake I would say that this flyback is blown up.

It is very common failure mode of TV's and monitors btw.

Re: Flyback problems
Munkey, Sat Mar 17 2007, 05:30PM

Well the reason I have got the flyback is because our TV blew up...
But if I touch my primary to a 2200uf capacitor charged to 30V it makes a small 3mm spark, so the secondary is working.