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Author Topic: Simulating wound inductors/transformers  (Read 3384 times)
NV1P
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Posts: 73




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« on: March 15, 2010, 01:00:17 PM »

I'm building a radio receiver out of discrete components and need to simulate each stage. How would I be able to simulate wire wound inductors? How can I calculate the approximate inductance when given the type of core and number of turns of wire? What if its an inductor with a tap?
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KF6QEX
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Posts: 651




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« Reply #1 on: March 15, 2010, 06:54:56 PM »

Keep handy in case the internet goes down: http://www.arrl.org/catalog/?item=NO-HB2010#top

simulate : http://www.linear.com/designtools/software/#Spice

calculate: http://www.crystalradio.net/cal/indcal2.shtml
 http://en.wikipedia.org/wiki/Inductor

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WA7NCL
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Posts: 625




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« Reply #2 on: March 18, 2010, 08:04:41 AM »

For air wound inductors there is an old time formula for inductance given dia, winding pitch and length. See the ARRL handbook. There are some old papers from the 30s that attempt to quantify the losses vs winding geometry and wire dia.  You might find these by poking around the internet.  Be aware this is complicated stuff to compute since it is actually an electromagnetic problem and any formulas or simulation programs would limitations to certain geometries etc.

For inductors with cores, its even harder, since there is a magnetic material involved that can be non-linear.  Here you need to consult the data from the core manufacturers.

For simulation, you can't do better than LT-Spice from Linear Tech.  You should visit their web site.  There are engineering books on spice such as "The SPICE book".  Search amazon etc.  There has also been a series running in QST that uses SPICE to explore simulating electronics.  Check it out.

Tapped inductors in SPICE are handled by the coupled inductor model.  A parameter K is used to define coeficient of coupling.  This is a mathmatical abstraction derived from mutual inductance.  BTW the coupled inductor model also covers transformers (tapped inductor is actually an auto transformer).

You sound like you're relatively inexperienced (at least in simulation).  Inductors can be tricky depending on what you are trying to simulate.  I would suggest you get some equipement like an impedance analyzer and make measurements on your prototype inductors and then use the measurements to extract the values for loss and series resonance etc.

You need to think closely about the aims of your simulations.  In some cases you just are looking for gross behavior.  In that case simple models with just an inductance and guess at loss resistance (Q) is good enough.  When you are pushing limits, you need more parasitics modeled.

Finally, you need to understand there are several fundamentally different domains in which simulation occurs.  Hams tend to think in the AC steady state (frequency) domain of reactances, swrs, reflection coefs. etc.  There is also a transient (time) domain where the actual time response is computed.  Each has its place.

AC steady state is linearized and is faster but does not model non-linear behavior.  Thus can't model thinks like mixers and intermod.  Transient simulation takes much longer and won't directly give you things like SWR etc.

Be prepared for a voyage of discovery.  All this seems pretty complicated I admit, but that's why electronic engineers need 4 to 5 years of training at the college level + 5 to 10 years of real world experience before they are proficient at this stuff.

That being said, have at it.  If you are willing to scale the wall, you can simulate the things you are interested in.
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KF6QEX
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Posts: 651




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« Reply #3 on: March 18, 2010, 07:58:00 PM »

Or

Keep handy in case the internet goes down: http://www.arrl.org/catalog/?item=NO-HB2010#top

simulate : http://www.linear.com/designtools/software/#Spice

calculate: http://www.crystalradio.net/cal/indcal2.shtml
 http://en.wikipedia.org/wiki/Inductor


for short Smiley
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