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Old 23rd November 2005, 02:23 PM   #1
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Default transformer help

I need a quick lesson on transformers - here's my questions:

1. What is the difference between magnetizing inductance and mutual inductance? Why do I ask? In spice, they model transformers as mutually coupled inductors. I don't see the relationship between mutual coupling and magnetizing inductance. Most people seem to spec transformers with magnetizing inductance, leakage inductance and turns ratio. I'd like to model this in spice, but don't know how to translate one to the other.

2. What does an air gap do for the transformer?

3. Any pointers to a good transformer discussion?
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Old 25th November 2005, 01:42 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
I wish I knew.
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Old 26th November 2005, 03:50 PM   #3
Tweeker is offline Tweeker  United States
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I dont know about modeling it in spice, but, an airgap will dramatically reduce the inductance of the coils. Mutual inductance will then also fall. The tradeoff is that it will become much more resistant to saturation.
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Old 26th November 2005, 04:03 PM   #4
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go to

www.sound.westhost.com

see the articles section and find the topic on tansformers.read whole of the two part,very informative article which deals with technical as well as real world issues with transformers
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Old 27th November 2005, 10:54 PM   #5
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Thanks for the pointer. Not exactly what I am looking for, but at least it's something.
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Old 28th November 2005, 12:27 PM   #6
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Old 28th November 2005, 07:07 PM   #7
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Try this link from TI/Unitrode. It discusses many aspects of transformer design. These seminars taught me a wealth of information. You should browse some of the other past seminars, too.

Here's the link again:
focus.ti.com/docs/training/catalog/events/event.jhtml?sku=SEM401014
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Old 1st December 2005, 06:47 PM   #8
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Here's a good document that helps:

http://www.pulseeng.com/pdf/G022.pdf
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Old 10th December 2005, 03:27 AM   #9
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Question Transformer redesign

As far as transformer winding is concerned, I am confident that I could do it, (especially w/the magnetics design handbook link posted by carvin guy, it answers a lot of my questions) because I am already experienced in AC Motor rewinding. But all of my knowledge is industrial; I'm wondering what makes an output transformer "high end". What makes tranformer quality go beyond the formula "Turns in primary/Turns in secondary=V in primary/V in secondary"?

I don't have any projects on the agenda, but I was considering building my own amp sometime soon; and I was thinking that I would transplant and redesign the transformers from my current amp; if the cost should end up being less vs. the cost of brand new transformers.

So, what makes a transformer "high-end"?
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Old 13th December 2005, 04:29 AM   #10
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I assume that you refer to audio transformers not power transformers as used in power supplies. High end audio transformers follow conventional rules as far as turns and impedance ratio goes. Good low frequency performance hinges on a fairly high primary inductance ( set by the core size and primary turns). Good high frequency performance hinges on low interwinding capacitance and low leakage inductance. Both of these can greatly reduced by interleaving the primary and secondary windings, interwinding capacitance is also reduced by using low dielectric insulation between the windings. For anything approaching HIFI standard the primary must be split into at least 4 windings with the secondary split into 3 or 5 windings. eg. The windings being interleaved like this S-P-S-P-S-P-S-P-S . They are not hard to wind you just need care and PATIENCE. Guitar or PA transformers can get away with less interleaves eg P-S-P-S is usually sufficient.
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