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555 flyback transformer MOSFET gets hot.

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Daedronus

Thu Oct 06 2011, 09:18AM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
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Posts: 370

I got much better results with a buffer between the 555 and the mosfet's gate.

Using two irfp260 in parallel instead of the 540 will also probably help a little.

I never managed to kill a irfp260 with input voltages up to 35v

Alex M

Thu Oct 06 2011, 09:19AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Yes, but as soon as I added the capacitor it killed my MOSFET.

Can anyone show me where to connect a TVS to protect the MOSFET?

Alex M

Thu Oct 06 2011, 09:21AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Daedronus wrote ...

I got much better results with a buffer between the 555 and the mosfet's gate.

Using two irfp260 in parallel instead of the 540 will also probably help a little.

I never managed to kill a irfp260 with input voltages up to 35v

What do you mean by buffer, do you mean some sort of transistor?

astralhighway

Thu Oct 06 2011, 09:35AM

Registered Member #4107 Joined: Sun Sept 25 2011, 07:30PM
Location: London
Posts: 53

One more thing, you need to be able to alter the fequency of your driver circuit. That's currently at a fixed frequency. At a certain (currently unknown) frequency, your primary circuit will become resonant and you will get much better results and lower power losses.

Alex M

Thu Oct 06 2011, 09:52AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

astralhighway wrote ...

One more thing, you need to be able to alter the fequency of your driver circuit. That's currently at a fixed frequency. At a certain (currently unknown) frequency, your primary circuit will become resonant and you will get much better results and lower power losses.

Actually I can adjust the frequency via the two 50k pots, shame it draws 10 amp with the best output.

astralhighway

Thu Oct 06 2011, 11:28AM

Registered Member #4107 Joined: Sun Sept 25 2011, 07:30PM
Location: London
Posts: 53

Alex, yes, I missed that detail. Hmmm, does changing the frequency increase the spark length? Possibly your transformer is still not resonant at any frequency you are selecting... you may have to investigate and if necessary, change your RC combination in the 555 timer circuit?

Patrick

Thu Oct 06 2011, 03:00PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

the schematic i showed you of my driver shows the proper use of TVS's.

you may have too slow of a rise time on the gate of the FET, this keeps the FET in the linear resistance portion longer causing heating. A buffer increses the current to the gate with a very fast step voltage, thus driving the transistor properly.

Lets not go resonant till he figures out all the other problems first, or he'll just blow components out all the time, searching for a magic frequency.

which TVS's did you buy?

the IRFP260 does look better, Vds =200v I do worry the diode inj your IRF540 maybe part or largely the problem though.

As a previous thread pointed out, you could be saturating the flyback, so how many primary turns do you have?

Alex M

Thu Oct 06 2011, 07:37PM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

I have 10 turns of 24SWG on the flyback core as suggested by many people online in order to get a higher voltage output.

I had the pots tuned just right and that was the biggest arc I could get out of the flyback and when the electrodes were brought close together the arc would be like a flame.

Sorry, what does linear resistance portion mean? is it something to do with the MOSFET not being driven correctly and that causes heating?

I have not got and TVS yet as I want to be sure that I am buying components that are going to do the job in protecting the MOSFET.

And just a though, what about a small capacitor across the drain and source of the MOSFET?

Thanks.

Daedronus

Thu Oct 06 2011, 09:48PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

Alex1M6 wrote ...

What do you mean by buffer, do you mean some sort of transistor?

See this:
Buffers

Alex M

Thu Oct 06 2011, 10:00PM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Thanks.

Again sorry if I seem to be asking silly questions but I am really interested in this sort of thing and am learning.

Could I possibly use IRFP250N instead? as they are much cheaper for me to get hold of.

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