Rachit,
Any idea on when those links were created?
Fairchilds 2001 datasheet has the 2N3904's spice model as ...
NPN (Is=6.734f Xti=3 Eg=1.11 Vaf=74.03 Bf=416.4 Ne=1.259 Ise=6.734 Ikf=66.78m Xtb=1.5 Br=.7371 Nc=2
Isc=0 Ikr=0 Rc=1 Cjc=3.638p Mjc=.3085 Vjc=.75 Fc=.5 Cje=4.493p Mje=.2593 Vje=.75 Tr=239.5n Tf=301.2p
Itf=.4 Vtf=4 Xtf=2 Rb=10)
It's like anything else in life, you use those models at your own discretion.
How does it replicate against the test circuit shown on the datasheet?
No, that solution is not easy. If I have to modify the model, then what will I end up with? A 2N3904, or something that does not exist? I would not live long enough to test it for every condition. How does marketing, selling, and guaranteeing anything define what kind of transistor I want to evaluate?
The dc model is defined by the parameters IS, BF, NF, ISE, IKF, and NE which determine the forward
current gain characteristics, IS, BR, NR, ISC, IKR, and NC which determine the reverse current gain
characteristics, and VAF and VAR which determine the output conductance for forward and reverse
regions. Three ohmic resistances RB, RC, and RE are included, where RB can be high current dependent.
Base charge storage is modeled by forward and reverse transit times, TF and TR, the forward transit time
TF being bias dependent if desired, and nonlinear depletion layer capacitances which are determined by
CJE, VJE, and MJE for the B-E junction , CJC, VJC, and MJC for the B-C junction and CJS, VJS, and
MJS for the C-S (Collector-Substrate) junction. The temperature dependence of the saturation current, IS,
is determined by the energy-gap, EG, and the saturation current temperature exponent, XTI. Additionally
base current temperature dependence is modeled by the beta temperature exponent XTB in the new model.
The values specified are assumed to have been measured at the temperature TNOM, which can be specified
on the .OPTIONS control line or overridden by a specification on the .MODEL line.
What good does it do to even have models in simulation programs if they are not correct?
No, I assumed their hand calculations were correct.
I can expect to get differences if the component parameters are different. I have not yet tested what would happen if I used the same model for each simulator.
Joe Jester,
"Spice programs use the Gummel-Pool analysis for transistors. Spice f3 uses Gummel-Pool. When some parameters are absent, the analysis reverts to Ebers-Moll."
Yes, those are good analysis models. But, I am not remarking about the way simulation programs do what they do. I am observing that the component models they use vary widely.
"I take everything I read on the internet with a large grain of salt and smaller grains for all other readings, although at another forum, there have been multiple mistakes from a college text, which could be either the author, the editor, or the typist. Who do you think will get the blame in that scenario?"
Of course. The author is responsible for proof reading with respect to mistakes in content.
"The webpage that you recommended reading suggested the same thing ... modifying the 2N3904 to something that does not exist. Some may use empirical data and modify the model for agreement. In those cases, it is useful, as long as another user of that model knows it's either created or modified by someone, like some of the models you'll find for LTspice at the user's group. Of course, the reputation of an author is at stake at the group. The marketing, selling, and guaranteeing is for you to profit from your hard work of modifying, if you wanted to pursue it."
I believe only the manufacturer should be changing the component model parameters. If the user does it, the results might be correct, but they are still bogus. One can get the correct results for the wrong reason. The manufacturers should put out a standard model, and be shamed into revising it if it can be shown to be nonsense.
"Using both models as seen on that page did not make a difference in that circuit when compared to the Fairchild model. Do you know the author of that webpage? Have you done the calculations as displayed on that webpage? I wouldn't consider an error of 20.8 percent as a good agreement."
They knew that component model was bogus, but they should not have tried to "fix" it. I have no idea who posted that page. No, I assumed their hand calculations were correct.
"From the Spice f3 manual concerning bjt's ..."
All those parameter explanations are interesting, but it does not negate the premise that they should be standardized for each semiconductor type.
"Did you create a design, simulate it, and build it, only to find large discrepancies between the simulation and actual? If you didn't design it, where did you get the schematic?
The last simulation I built was in good agreement with the breadboarded circuit. What simulation software do you use? "
I said in my first post that those differences were not large. As for those other questions, what difference does it make? I can expect to get differences if the component parameters are different. I have not yet tested what would happen if I used the same model for each simulator.
Ratch
from: IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 47, NO. 2, FEBRUARY 2000
A new bipolar transistor model called VBIC has recently been developed and is likely to replace the Gummel–Poon model as the new industry standard bipolar transistor model. This paper focuses on the comparison of the VBIC and Gummel–Poon models under the dc operations. The extraction and optimization procedure coded in S+ statistical language and required for VBIC simulation is also developed and presented.
Hi Ratch,I still advocate for standardization of semiconductor models.
New models are welcome, but will it play with LTSpice and other simulators?
Anyway, the future is just a promise, but we have to live with what we have today.
from **broken link removed**
A SPICE simulation program however is not a "magic box", is not enough to copy an electronic sheet to obtain automatically the right result. Vendor's model libraries are very reliable but often the designer have to model by himself some device, like a transformer, or have to model electronic phenomena that are not related to physical devices but anyways have a big deal with the global circuit. In addition, SPICE is a finite difference numerical method, so there are simulator parameters that is important to learn about to improve the simulation results and avoid convergence problems. This is why professionalism and experience of designers are so important as the reliability of the libraries models.
I would also agree, standardisation of simulation models is essential if we are to have a high degree of confidence when running LTSpice simulations.
Don't you think the parameters listed in the Spice f3 manual constitutes a "standardizing" of a model even if all the parameters are not used? LTSpice isn't the only spice out there. It is a custom written Spice that may run other spice models. It doesn't run all models equally well. It may satisfy your needs and yet not satisfy others.
If your are considering in isolation the LTS models then of course its pretty obvious they are standardised within LTSpice, but thats not the point thats being made.
Simulation with the supplied models is fully supported
All bug reports are appreciated and will be resolved
Only in a utopia would every spice produce precisely the same results to the "atto" accuracy. But then, in a utopia, we all be using the same Spice and this discussion wouldn't exist.
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