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Modeling >> Behavioral Models >> tranformer modeled with coupled inductor issue
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Message started by analog9080 on Apr 14^th, 2016, 10:52am

Title: tranformer modeled with coupled inductor issue
Post by analog9080 on Apr 14^th, 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

Title: Re: tranformer modeled with coupled inductor issue
Post by Ken Kundert on Apr 14^th, 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

Title: Re: tranformer modeled with coupled inductor issue
Post by analog9080 on Apr 14^th, 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

Title: Re: tranformer modeled with coupled inductor issue
Post by Ken Kundert on Apr 15^th, 2016, 10:58pm

Simply specify a turns ratio that is not equal to one.

-Ken

Title: Re: tranformer modeled with coupled inductor issue
Post by analog9080 on Apr 16^th, 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 ?

Title: Re: tranformer modeled with coupled inductor issue
Post by Ken Kundert on Apr 16^th, 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

Title: Re: tranformer modeled with coupled inductor issue
Post by analog9080 on Apr 17^th, 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

Title: Re: tranformer modeled with coupled inductor issue
Post by Ken Kundert on Apr 17^th, 2016, 5:52pm

Try analogLib -> xfmr.

-Ken

Title: Re: tranformer modeled with coupled inductor issue
Post by analog9080 on Apr 17^th, 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

thanks