hi everyone,

i found an LTspice model for TIP41 on Linear Technology's site,

.MODEL Qtip41c npn
+IS=7.55826e-11 BF=260.542 NF=1.11221 VAF=100
+IKF=0.526814 ISE=1e-08 NE=2.18072 BR=26.0542
+NR=1.5 VAR=1000 IKR=3.54059 ISC=1e-08
+NC=1.63849 RB=4.56157 IRB=0.1 RBM=0.1
+RE=0.0162111 RC=0.0810556 XTB=0.1 XTI=1
+EG=1.206 CJE=1.93296e-10 VJE=0.4 MJE=0.259503
+TF=1e-08 XTF=4.06972 VTF=7.1157 ITF=0.001
+CJC=1.09657e-10 VJC=0.730921 MJC=0.23 XCJC=0.803085
+FC=0.8 CJS=0 VJS=0.75 MJS=0.5
+TR=9.01013e-08 PTF=0 KF=0 AF=1
+ mfg=onsemi
* Model generated on Dec 27, 2003
* Model format: PSpice

questions:-

1) is BF in the first model line the beta number? my TIP41 tested beta=134, not 260, on my multimeter, and i'd like to make the model match my transistor that's actually being used. should i change this BF value to 134 and expect my LTspice runs to match the real word transistor being used pretty closely? the catch is that i don't have any necessary equipment to measure the real circuit built, guess i'm forced to rely on closely matched LTspice simulations then, thus the question.

2) i can't find LTspice models for most of junk grade bjt's i happen to have now, so i'm wondering how i could write them myself. how do i find out names of parameters and parameters accepted by LTspice? what do i do if spec sheets are too simple, without details like the TIP41 one from linear technology above?

3) can Spice and Pspice models be used with LTspice as well

thank you for all the help

 

1) Yes, the BF parameter is Beta Forward, which is the normal Beta value. You can change it to match the transistor you have, if desired.

2) BJTs don't vary a lot, so just select a Spice model that's close to the basic parameters of the transistors you have, which should be good for most simulations, other than perhaps high frequency switching or RF . It requires complex measurements to generate the specific BJT spice parameters otherwise.

3) Spice and Pspice models should work fine in LTspice. They all use the same Spice parameters.

 

thank you crustschow, great help!