BJT SPICE Models, reality-check

[keantoken]

And here is the accompanying 5771 model.

.model 2N5771 PNP(Is=1.2f Xti=3 Eg=1.16 Vaf=100 Bf=125 Rb=45
+ Ikf=100m Ise=62f Ne=1.7 Xtb=1.7 Br=1.365 Nc=2 Isc=0 Ikr=0 Rc=3.75
+ Cjc=2.77p Mjc=.1416 Vjc=.75 Fc=.5 Cje=2.65p Mje=.3083 Vje=.75 Tr=4.033n
+ Tf=118.5p Itf=.5 Vtf=3 Xtf=6 Rb=10 Vceo=15 Icrating=200m mfg=Fairchild)

The Babylonian Method takes patience at first but it gets SOOOO much easier after you figure out the pattern. I've attached a virtual test fixture you can verify the models with.

The only thing I don't know how to fix for this model is the Hfe behavior at 125C.

I think my old models can be used as "worst case" models, since the Hfe is so low...

- keantoken

[janneman]

/Hat off
Pretty good job, keantoken!
/Hat on.

jd

[keantoken]

Thanks!

- keantoken

[keantoken]

The BJT default in ISSPICE4 gives first order, Ebers-Moll, DC
parameters; but it does not provide parameters for Transient or
AC analysis. The following default can be used when minimal
data sheet specifications are available by using the PARAM
program to evaluate the equations in curly braces. This model
will create a good transistor model from virtually any data sheet.
The parameters you must specify are:

IMAX Maximum collector current
COB Collector-base capacitance
FT Gain bandwidth product in Hz
TS Storage time

The equation-based model is shown below:
.MODEL NBJT NPN (CJC={2.2*COB} TF={.16/FT} TR={1.7*TS}
+CJE={7*COB} RC={.5/IMAX} VAF=100 IKF={.7*IMAX}
+ IS={2E-15*MAX} )

This subcircuit-based macro model makes use of the default
model parameters so that it is not permissible to change default
values without reevaluating the parameters which are given
here.

I was page-flipping randomly through that PDF and found this.

I suspected at first there was a correlation between Icmax and IKF, but looking through the LTSpice library convinced me otherwise. Not sure about Is.

It would be great if I could figure out some way to shove Ise in there...

More page-flipping will follow.

I would still rather babylize it than figure out all that math (my grandma always said that lazy people work 3 times harder...).

- keantoken

[keantoken]

Okay, I think those models are good enough. Here is my current attempt at the BC547C, using this datsheet:

http://www.onsemi.com/pub_link/Collateral/BC546-D.PDF

.model BC547C NPN(Is=32f Xti=3 Eg=1.11 Vaf=100 Bf=720
+ Xtb=1.5 Br=6.313 Isc=138f Nc=2.053 Rb=1.3k
+ Ikf=500m Ise=230f Ne=1.583 Nk=1.05
+ Ikr=.187 Rc=.4216 Cjc=5.25p Mjc=.3147 Vjc=.5697 Fc=.5 Cje=11.5p
+ Mje=.3333 Vje=.5 Tr=10n Tf=410.7p Itf=2.204 Xtf=66.65 Vtf=10)

One question... Isn't Rb a little large?

- keantoken

[klewis]

keantoken,

Do you have a model for the 2SC3503? Fairchild doesn't seem to have it on it's site... I found the complimentary other half of the pair 2SA1381 on their site. Funny...

Thanks,

Ken

[klewis]

Originally Posted by klewis

keantoken,

Do you have a model for the 2SC3503? Fairchild doesn't seem to have it on it's site... I found the complimentary other half of the pair 2SA1381 on their site. Funny...

Thanks,

Ken

Keantoken,

I found them...

So, I know this is off topic, but, was wondering if you could help. I'm using a LME49811 for the front end of my amp - first and second stage - and was looking for a simple way to simulate the third stage including the bais scheme. I found this image from Bob Cordell, but don't know how to get it to work. I've also attached a zip of my model. Any thoughts? I would like to model the bais along with the output stage. I've been able to get the bais model to work by its self and the third stage as well...

Ken

[keantoken]

That was interesting. In the VAS, you are applying positive feedback instead of negative feedback (your image is wrong it seems). Try this.

I used different models, so you'll have to change them back.

- keantoken

[klewis]

Originally Posted by keantoken

That was interesting. In the VAS, you are applying positive feedback instead of negative feedback (your image is wrong it seems). Try this.

I used different models, so you'll have to change them back.

- keantoken

I'll give it a go later this afternoon. Interesting, the image was from Bob Cordell... maybe wanted to throw neophites like me for a loop.

By the by, one of the things I want to try is driving the allison configuration with the LME49811, do you think it will work?

Thanks again.

Ken

[keantoken]

I think it would be great for driving the Allison! You should get great distortion specs... Although the best way to drive the Allison is between the emitters of the bias transistors, you might get lower distortion specs that way.

One thing I should say about the Allison is that there are a billion different ways you can use it, all of which it would take time to document. Feel free to consult me about the Allison, maybe I should draw up all the different schematics and forms I've seen it take and compile into one huge PDF. I wouldn't worry about the sonic qualities of it, the best sound I have ever heard was played with an LTP frontend through an Allison, out of a 3" speaker...

- keantoken