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SPICE simulation of finite Q inductors

Those of you who simulate things like passive LC filters... when you want a simulation that includes the finite Q effect of the inductor, do you tend to use a model that computes the equivalent parallel resistance, Rloss, based on the Q specified on a data sheet at a given frequency (and then use that at

*all* frequencies of your simulation, effectively creating Q(freq) )? Or do you simply specify Q and then use that at all frequencies (creating Rloss(freq) )?

For the following, assume you first calculated Rloss at a frequency f0:

The actual Q of an inductor varies with sqrt(freq) until you start approaching self-resonance, so assuming Q is fixed, you underestimate Q above f0 and overestimate below f0. Using just Rloss, you overestimate below f0 and underestimate above f0.

---Joel

Reply to
Joel Kolstad
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In most cases, the Q is important only near the resonant frequency. I use a single fixed value resistor in series with the L that sets the Q at the frequency corresponding to the circuit resonance frequency.

Mark

Reply to
Mark

In critical applications I'm inclined to use a multi-lump model to make sure I catch any "squirrels" ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

on

Too bad you can't make that work on Usenet. We're overrun with squirrels. :(

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

to

on

do

I've suddenly acquired jack rabbits in my front yard. Can't figure out where they're nesting.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Be VERY careful, Jim. Eeyore sent them to spy on you!

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

THAT explains it ;-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Reply to
Jim Thompson

You better oil up your Uzi, he wants them to build a roundabout in your yard.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

I think the greeting sign (in Hebrew) out on the front patio will probably drive him back ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Do you think that I should tell the little moron that I was trained to kill with the M16, the M60, and how to use the M72, yet I've never had to kill anyone?

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

I can't find the original message so I will continue here. The first order model should include the winding resistance as a series resistor, and then compute a parrallel resistor due to the core losses. Verify over the frequencies your interested in, materials vary a lot. In fact if a series resistance is sufficiently accurate, you can use pre-distortion (right term?), tilting the frequency axis, and design the filter having perfect (inf Q) components; and then undistort the results to get values. That sounds a little jumbled, but these days I presume that technique is obsolere. I reliably designed a 9 pole filter in the 70's this way; with both time and frequency requirements.

Ray

Reply to
RRogers

Coilcraft has some nice SPICE models for their inductors. You could modify one of those.

Leon

Reply to
Leon

Coilcraft has some nice SPICE models for their inductors. You could modify one of those.

Leon

Reply to
Leon

on

Well, you might as well just accept them, and hope your plants grow faster than they can eat them... 8-)

Charlie

Reply to
Charlie Edmondson

to

on

do

I don't think they eat cactus or mesquite ?:-)

If they do, I'll just get out the shotgun ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

If they eat cacti, ship them to Lake County Florida. There is enough there to feed millions of the willey wabbits down there. :(

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

a

to

based on

do

Young mesquite, probably. Cacti, they usually use to cover their burrows. The problems are if you have any flowers or food plants growning. In Borrego, we had several families, but there was only one of the plants that they liked so well that it couldn't grow. But, once we planted some marigolds. Lasted two days...

Charlie

Reply to
Charlie Edmondson

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