Transformer Help

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lkraemer
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Transformer Help

Post by lkraemer » Sun May 01, 2005 3:30 pm

I need to locate a transformer that meets the following requirements:<p>1. Small Physical Size (Toroid/E-Core/Other)
2. Low/Reasonable Cost
3. 30:1 Step-up Transformer
Input 6 VDC (Chopped Square Wave) running at
around 17.5 KHZ
Output approx. 180 VDC (Chopped Square Wave)
Input - Primary approx. 15 Turns of #24 Magnet
Wire
Output - Secondary approx. 450 Turns of #34
Magnet Wire<p>If I wind a Toroid, what type Material do I use? (Powered Iron Core)
I would like to have the size as close to a FT-50 or FT-82 as possible.<p>Can anyone help me Locate/Design/Wind this Transformer?<p>Any help you can give will be greatly appreciated.<p>Thanks.<p>Larry Kraemer
[email protected]

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sofaspud
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Re: Transformer Help

Post by sofaspud » Sun May 01, 2005 4:23 pm

I'm not much help, but could a reversed 120:4.5 stepdown xformer be used?

rshayes
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Re: Transformer Help

Post by rshayes » Sun May 01, 2005 4:34 pm

Try looking at the Magnetics, Inc. web site (www.mag-inc.com). They have data sheets on several types of cores, and ap notes on transformer design.<p>You probably don't want powdered iron. It is cheap, but it also tends to be lossy when the flux excursions are large. It makes good filter chokes where high DC currents are present.<p>At that frequency, ferrite may be the best choice. Tape wound cores could be used, but will probably be expensive.<p>A ferrite toroid is certainly a possibility. You don't seem to be asking for large wire sizes. Ferrite pot cores are easier to wind. Ferrite E-I cores tend to be cheapest, and only slightly harder to wind than pot cores. There are also other cores that are easier to mount. Toroids can be a problem in this area.

Mike
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Re: Transformer Help

Post by Mike » Sun May 01, 2005 6:24 pm

not possible.<p>transformers only work on AC, not DC.

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sofaspud
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Re: Transformer Help

Post by sofaspud » Sun May 01, 2005 7:04 pm

The DC is alternating, in the sense that it goes from 0V to 6V and back to 0V, 17.5K times per second. Not in the sense that it changes polarity.
And yeah, it'd probably be difficult to find a transformer like I suggested that operates at 17.5kHz, but it seems like the design part has already been done. My intent was to "broaden the search."

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jwax
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Re: Transformer Help

Post by jwax » Sun May 01, 2005 7:18 pm

Understand you will not see anything like a "square wave" coming out of a transformer.
You neglected to mention the power level you are interested in transforming. Any more details? Whatcha building?
WA2RBA

dyarker
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Re: Transformer Help

Post by dyarker » Sun May 01, 2005 7:24 pm

It might have been more correct/clear if Larry said, "6V chopped square wave", leaving out the "DC" bit. It will be a unipolar square wave AC going to the transformer.<p>Larry, if the 180V output is too weak, try a 30 turn center tapped primary. Feed it upper half 6V-off-lower half 6V-off-upper half 6v-etc-etc.<p>C U L,
Dale Y

lkraemer
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Re: Transformer Help

Post by lkraemer » Mon May 02, 2005 4:06 pm

Stephen, thanks for the web site and your help.
I am looking at that site for more information.<p>Dale, I need this transformer to be around 3/4
inch or so, for this application. I am trying to make a CDI Ignition for small weedeater type engines.<p>Thanks.<p>LK

rshayes
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Re: Transformer Help

Post by rshayes » Tue May 03, 2005 6:01 am

For that application, you may want to consider a flyback type of supply charging the capacitor. This uses a dual winding inductor, which is usually wound on a gapped core. Usually this will be a ferrite pot core or ferrite E-I core.<p>Application notes describing switching supply design be found on the International Rectifier web site (www.irf.com). The Texas instrument site used to have the old Unitrode seminar notes available for download. These were originally distributed in the 1980s and cover a lot of basic design information.

dyarker
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Re: Transformer Help

Post by dyarker » Tue May 03, 2005 9:11 am

Does the 180V charge a capacitor that the CDI then dumps into an ignition coil primary?<p>A 3/4 inch core and 34AWG sounds a little "light" for even a small spark plug.
Dale Y

lkraemer
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Re: Transformer Help

Post by lkraemer » Wed May 04, 2005 6:14 am

Dale,
That is exactly what I want to do. I plan on charging a .68 MFD cap, then dump it into an External Coil.<p>
Stephen,
I am having trouble finding the Application notes describing switching supply design on the International Rectifier web site (www.irf.com).
Can you give me the specific URL?

LK

rshayes
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Re: Transformer Help

Post by rshayes » Wed May 04, 2005 7:49 am

On the International Rectifier site (www.irf.com), try a site search for "an 1024" and "an 1025". These ap notes describe a typical flyback converter design. Also try a site search for "flyback".

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