Does anyone have a spice model for a ‘real’ inductor where you can specify the loss (Q) and self resonate frequency without having to use a separate resistor and capacitor ? I want to use the L_trim symbol on the schematic and specify the L, Q (AC resistance ) and self resonant frequency. I have a footprint and 3D model for the actual part. See below:
Firstly: ask Coilcraft for a spice model.
If they don’t have, you may create your own model. This then would have two steps.
The electrical engineering part (your turn):
You cannot create a ‘real world’ model without extra parasitic elements R and C.
So you should draw a circuit diagram with all L, R, C needed.
Then you should write down the equatiosns which lead to R, L, and C as fuctions
of the inductance L, the quality factor Q and the resonance frequency Wr.
Please post the equations here.
Only then the ngspice part is following:
You need to create a spice syntax model description. This is typically a
subcircuit model with two nodes and L, Q, and Wr as parameters. This model
then may be attached to your symbol, the parameter being visible on
the Eeschema canvas. I may give you some support here.
A quick search:
https://html.duckduckgo.com/html?q=inductor+spice+model
finds lots of related info. For example, the 4 page PDF below, both has some math, and subcircuit examples.
http://www.intusoft.com/articles/inductor.pdf
Thanks for the reply holger. Coilcraft do not have a SPICE model for this particular part. This particular part is a single layer 2 1/2 turn coil tuned with a small carbonyl J slug. Inductance range is 70n-78n; 67n with slug removed. Q is specified as 98 @50MHz & 74n. SRF is specified as 1200MHz with slug removed. DC resistance is specified as 8.6mΩ.
Q=ωL/r, for series L,R so r=ωL/Q. However, this is a function of frequency, which complicates things. Also, need to scale r if using at a different frequency. Using above data, r=(2π*(5010^6)(7410^-9))/98=.237Ω. Calculate r from rDC value assuming only skin depth effect. For 22 AWG Cu wire, Rac/Rdc=17.254 @50MHz. Therefor r=17.2548.6*10^-3=.148Ω<.237Ω. So r calculated from Q could include (i) proximity effect of inductor turns (ii) some core loss (iii) some measurement error.
Perhaps better to just specify value of r and calculate value of r separately.
SRF=1/(2πsqrt(LC)), so C=1/(L(2πSRF)^2). Assumes slug does not effect C as coil is tuned.
Difficult to model core loss of carbonyl J slug as can’t find permeability vs frequency data; also loss will change as coil is tuned and position of slug changes wrt magnetic field.
Use sub-circuit as below for model. Is it possible to enter value of r and SRF along with L as opposed to having r and SRF permanently defined in the model ??
