[SI-LIST] Re: Transformer Spice Model
- From: steve weir <weirsp@xxxxxxxxxx>
- To: beneken@xxxxxxxxxxxx,
- Date: Fri, 30 Jan 2004 04:41:00 -0800
Thomas,
The formula for K that I have always known is ( 1 -
Lpri_sec_shorted/Lpri_sec_open )
That would yield a coupling factor of 0.992. High quality transformers can
usually hold Ls/Lp to about 1%.
I have never seen the formula that you used, and it does not make physical
sense to me as it just returns the turns ratio. The formula that you used:
K = ( LP / LS ) ^0.5 = ( LP / ( LP / N^2 ) ) ^0.5 = N
Regards,
Steve.
At 10:28 AM 1/30/2004 +0100, Thomas Beneken wrote:
>Hi John,
>
>this is what I took from the data sheet you provided:
>Primary side open circuit inductance L14 is 1000 uH.
>Stray (or Leakage) inductance Ls is about 8 uH.
>Turn ratio n is 0.9:1.
>
>Calculated:
>Effective primary inductance Lp is L14 minus Ls is 992 uH.
>Secondary side open circuit inductance L68 is Lp div by square of n is 1225
>uH.
>Coupling factor k is square root of Lp div by L68 is 0.996.
>
>SPICE model:
>L_L1 1 0 1000 uH
>L_L2 2 0 1225 uH
>Kn_K1 L_L1 L_L2 0.996
>
>Simulation results for the lower frequency limit:
>f/kHz a/dB
> 1 -11.5
> 10 - 0.59
> 100 - 0.09
>
>Simulation results for the higher frequency limit:
>f/MHz a/dB
> 0.3 - 0.18
> 1 - 1.22
> 2 - 3.55
>
>Remarks/Conclusions:
>DUT attenuation was simulated with a VNA model with 50 Ohm ports.
>But DUT will be used in a 100 Ohms environment.
>DUT bandwidth seems to be suitable for desired applivation.
>By data sheet harmonic distortion is better than 85 dB.
>So the linear model should do.
>
>Regards, Thomas
>
>-----Original Message-----
>From: Thomas Beneken [mailto:beneken@xxxxxxxxxxxx]
>Sent: Thursday, January 29, 2004 1:37 PM
>To: 'si-list@xxxxxxxxxxxxx'
>Subject: Transformer Spice Model
>
>
>Hi John,
>
>you may find this helpful for a start.
>
> >From measurements:
>L1 is the open circuit inductance of the primary coil
>L2 is the open circuit inductance of the secondary coil
>Ls is the stray inductance measured on primary side with secondary coil
>shorted
>
>Calculated:
>Lp is effective primary inductance with Lp equals L1 minus Ls
>n is primary to secondary turn ratio with n equals sqare root (Lp div by L2)
>k is coupling factor with k equals square root (Lp div by L1)
>M is mutual inductance with M equals square root (Lp times L2)
>
>SPICE model for L1, L2, Ls: 45uH, 20uH, 5uH, k results in 0.943
>L_L1 1 0 45u
>L_L2 2 0 20u
>K_K1 L_L1 L_L2 0.943 Kbreak
>
>Tweak the equations as needed (What is in that data sheet?). You can put in
>non-linearity by editing a core model (instead of Kbreak). Model parameters
>are e.g. flux area, flux path length, gap, saturation factor.
>
>Thomas
>
>
> > -----Original Message-----
> > From: si-list@xxxxxxxxxxxxxxx [mailto:si-list@xxxxxxxxxxxxxxx]
> > Sent: Wednesday, January 28, 2004 3:46 AM
> > To: si-list@xxxxxxxxxxxxxxx
> > Subject: [SI-LIST] Digest Number 985
> >
> > Message: 1
> > Date: Tue, 27 Jan 2004 11:40:58 -0600
> > From: Chuong Nguyen <johnnguy@xxxxxxxxx>
> > Subject: Transformer Spice Model
> >
> > Hi,
> >
> > Does any one know how to construct a transformer's spice
> > model from its
> > datasheet?
> >
> > thanks,
> > jcn
>
>
>
>
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