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transformer K in LT Spice

I recall seeing, somewhere, that LT Spice may handle a transformer with K=1 different from one where K

Reply to
jlarkin
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Please post your LTSpice list.

Reply to
John S

One possible explanation is that K=1 is physically impossible, while K=0.999 is attainable.

The problem with finite difference numerical integration is that rounding errors can accumulate, if there's no mechanism to attenuate them.

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The book was written in 1966, and Spice 1 wasn't written until 1973, so the application in electronics didn't make it into the title.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

Am 19.01.20 um 02:16 schrieb snipped-for-privacy@highlandsniptechnology.com:

I think one uses as many 9s as one expects decades of bandwidth (crude rule of thumb). Then your signal simply might simply be out of transformer BW. Check the inductances?

regards, Gerhard

Reply to
Gerhard Hoffmann

Potentiometers work the same way, at 0.0 or 1.0 one or the other resistor is exactly zero and the network is physically different. IIRC SPICE optimizes out supernodes like these. Easy fix: don't short nodes together, leave

1mohm or uohm or 1nH or whatever between them.

A nonideal transformer can be expressed as an ideal transformer with series and parallel inductances, and an ideal transformer is a pair of dependent ideal sources. Same thing, but with an arbitrary ratio between nodes.

As noted, K=1 is physically impossible anyway, so if you need K=1 for the sim, you've already failed. Find the smallest feasible K and solve backwards to a real transformer design.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/ 

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> 
> 
> I recall seeing, somewhere, that LT Spice may handle a transformer 
> with K=1 different from one where K if K=0.999 but not if K=1, and there's no obvious reason why. 
> 
> 
> 
> 
> --  
> 
> John Larkin         Highland Technology, Inc 
> 
> The cork popped merrily, and Lord Peter rose to his feet. 
> "Bunter", he said, "I give you a toast. The triumph of Instinct over  
> Reason" 
> 
> 
>
Reply to
Tim Williams

Failed? I'm experimenting with a control loop and noticed the difference, which has no immediately obvious explanation.

Learning is not failing.

I recall hearing about the K=1 vs K

Reply to
jlarkin

"Ideal transformers" aren't a good approach. Spice implements the transformer equation, which is a lot safer.

Except that you do seem to do a lot of failing to learn.

Spice has a tendency to get thrown by ideal - as in non-dissipative - components.

You seem to need something like a milliohm or so of series resistance in inductors and capacitors. K

Reply to
Bill Sloman

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