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ZVS flyback transformer (now broken)

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Thomas W

Thu Mar 24 2011, 10:44AM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

Hi guys/gals,

OLD
just wondering about zvs flyback transformers, (im planning to build one today)
what does the capacitor do?
and does it have to be a specific type e.g. metal film or something?
problem is maplins does not stock that specific value
so is it ok if i use a different value and to what range and effect does it have?
OLD

Edit:

ok i just finished soldering and went to test it..
unfortunately the ATX powersupply just cut out on me
one of the mosfets got a little warm
but apart from that nothing :S

and the ATX powersupply only starts when the FBT is not connected to the driver

thanks,
Tom Williamson

Edit: Spelling ;P

Ash Small

Thu Mar 24 2011, 11:33AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

It forms part of the resonant circuit with the centre tapped inductor. different values will work, but will affect the resonant frequency (I think!). The type is also important, as some types have more losses/get hotter at high frequencies.

Others here know more about this than I do.

Inducktion

Thu Mar 24 2011, 12:12PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Tom Williamson wrote ...

Hi guys/gals,

just wondering about zvs flyback transformers, (im planning to build one today)
what does the capacitor do?
and does it have to be a specific type e.g. metal film or something?
problem is maplins does not stock that specific value
so is it ok if i use a different value and to what range and effect does it have?

thanks,
Tom Williamson

Edit: Spelling ;P

The Capacitor is the C part of the LCR resonant circuit. A smaller value means higher frequency, and a larger value means lower frequency. Most flybacks run great at around 30-50 khz, and you can find resonant calculators online to figure out what your frequency will roughly be. .68 uF, like the original schematic says to use, will give you a value somewhere in there.

the Capacitor NEEDS to be a good quality cap, it doesn't necessarily need to be metal film, polyester, polypropylene, mica, just something that's better than an electrolytic or ceramic capacitor, as those two will more than likely blow up due to heat generated within.

MKP is just the best kind to use since it heat's up the least.

Thomas W

Thu Mar 24 2011, 01:15PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

would this one do?

does it matter if its audio grade?

James

Thu Mar 24 2011, 05:40PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Tom Williamson wrote ...

would this one do?

does it matter if its audio grade?

Those ought to do just fine, audio grade caps are usually pretty good, but you certainly don't need audio grade for this. I've built a few different ZVS drivers and never bought capacitors for any of them. Old CRT computer monitors and TV sets almost always have numerous good quality film capacitors in them.. Computer power supplies usually have a few too. 0.2 to 0.68uF seems to work well for most flyback/LOPT.

Inducktion

Thu Mar 24 2011, 05:46PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Tom Williamson wrote ...

would this one do?

does it matter if its audio grade?

That looks like it would work fine. Just check the cap's temperature every now and then.

Thomas W

Thu Mar 24 2011, 06:11PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

i just went over to the maplins store - they dont have any :S ive found a cap on a psu that looks close ish 0.47uf?

James

Thu Mar 24 2011, 07:00PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Tom Williamson wrote ...

i just went over to the maplins store - they dont have any :S ive found a cap on a psu that looks close ish 0.47uf?

There's a very good chance that will work fine. My first ZVS circuit was tack soldered together in air out of parts I happened to have laying around on the bench and it worked just fine. There's nothing particularly critical about it.

Thomas W

Thu Mar 24 2011, 07:16PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

Ignore (read top post)

Nah

Thu Mar 24 2011, 07:53PM

Registered Member #3567 Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260

Hi!

Is the ATV shutting down because your drawing too much current? Or do you think it is creating kickback that is shutting down the ATX ?

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