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tranformer modeled with coupled inductor issue (Read 6593 times)
analog9080
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tranformer modeled with coupled inductor issue
Apr 14th, 2016, 10:52am
 
Hello,
if I model a step down/ step up transformer using coupled inductors with k=1 as part of a fly-back/forward converter with ideal components, the power efficiency is not near 100% as expected.
If the step down ratio is 1:1 then it shows 100% efficiency. Is there an issue in the simulator when modeling a transformer, any work arounds ?
thanks
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Ken Kundert
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Re: tranformer modeled with coupled inductor issue
Reply #1 - Apr 14th, 2016, 1:45pm
 
Using coupled inductors with k=1 does not produced an ideal transformer. It yields a 'closely coupled inductor', which is a bizarre little creature and not what you want. Just use the ideal_transformer. That is what it is there for.

Oh, and please do not post simulation questions in the design boards.

-Ken
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analog9080
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Re: tranformer modeled with coupled inductor issue
Reply #2 - Apr 14th, 2016, 1:54pm
 
ok got it
The ideal transformer only has a coupling coeff k, how do I model a step down or a step up ideal transformer ?
thanks
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Ken Kundert
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Re: tranformer modeled with coupled inductor issue
Reply #3 - Apr 15th, 2016, 10:58pm
 
Simply specify a turns ratio that is not equal to one.

-Ken
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analog9080
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Re: tranformer modeled with coupled inductor issue
Reply #4 - Apr 16th, 2016, 7:22am
 
the component that I am trying to use is ixfmr in analogLib, it does not allow turns ratio as a parameter option. Only coupling coeff "k" is allowed ?
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Ken Kundert
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Re: tranformer modeled with coupled inductor issue
Reply #5 - Apr 16th, 2016, 11:08pm
 
I don't know the name in Artist, but it is not ixfmr.  The name in Spectre is transformer. In Artist, look for something like transformer or ideal_transformer.

-Ken
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analog9080
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Re: tranformer modeled with coupled inductor issue
Reply #6 - Apr 17th, 2016, 8:26am
 
just checked the following libraries, did not find any transformer/ideal_transformer or related components

analogLib
sample
ahdlLib
functional
basic

The cadence help documentation search did not show transformer mention

If there is a syntax available for  spectre simulation then I can create my own model ?
thanks

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Ken Kundert
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Re: tranformer modeled with coupled inductor issue
Reply #7 - Apr 17th, 2016, 5:52pm
 
Try analogLib -> xfmr.

-Ken
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analog9080
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Re: tranformer modeled with coupled inductor issue
Reply #8 - Apr 17th, 2016, 10:11pm
 
82.1% efficiency with xfmr, ideal switch (sw), ideal diode(modeled with an equation), ideal resistors and caps from analogLib ? efficiency changes ~1-2% as I change the Is current of the ideal diode

Transient sims were run on this switched transformer with moderate accuracy (trap only) with reltol=1e-3, vabstol=100u, iabstol=2n. clock rate was 100KHz with an ideal pulse waveform at 50% duty cycle in open loop just to observe Pin=Pout effect as a function of input voltage, transformer ratio, duty cycle

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