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[SOLVED] how to change parameter for transistor in ltspice

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Full Member level 3
Oct 31, 2010
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Trying to understand spice models to make a new model for ltspice. Not
understand so looked at existiing ones. Spice model to Fairchild
datasheet for 2N3904 is

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)

Spice model to ltspice for same transistor is

NPN(IS=1E-14 VAF=100 Bf=300 IKF=0.4 XTB=1.5 BR=4 CJC=4E-12 CJE=8E-12
RB=20 RC=0.1 RE=0.1 TR=250E-9 TF=350E-12 ITF=1 VTF=2 XTF=3 Vceo=40
Icrating=200m mfg=Philips)

Some parameters are not in both. Even ones that are in both are
different in each one. Not understand what any mean but anyway eg
Ise=6.734 in Fairchild yet Ise not exist in ltspice model. Is=6.734f
in Fairchild yet Is=1E-14 in ltspice.

If I get model to data sheet how to make into ltspice model?

Spice model for MPSA42 from Fairchild is this

NPN (Is=34.9f Xti=3 Eg=1.11 Vaf=100 Bf=2.65K Ne=1.708 Ise=16.32p
Ikf=23.79m Xtb=1.5 Br=9.769 Nc=2 Isc=0 Ikr=0 Rc=7 Cjc=14.23p Mjc=.5489
Vjc=.75 Fc=.5 Cje=49.62p Mje=.4136 Vje=.75 Tr=934.3p Tf=1.69n Itf=5
Vtf=20 Xtf=150 Rb=10)

How to make into ltspice model?

How it works?


LTSpice basically understands Spice syntax. Write a model statement before the parameter list and use one of these options:
- place it into a Spice directive in your schematic design
- write it to a file and include it in your design
- add it to the standard BJT library. It will be available, when browsing transistors. But if you update your LTSpice installation, it's overwritten, so make a backup.

Some additional hints can be found here LTwiki

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