Hello:

Not sure if this is the right place to ask a question about Spice but
here goes. What is the parameter name for AC Gain for a BJT model.
DC Gain = bf.

Thanks,

RS

 

Of course you know that negative feedback and a load impedance reduce the voltage gain of a BJT.
Also, I showed that a BJT with a high AC gain has a low amount of negative feedback then at fairly high output levels the distortion is extreme.

 

What is the parameter name for AC Gain for a BJT model.
DC Gain = bf.

There is no paramFor AC gain of a BJT,
LTspice calculates the collector operating current in the circuit, and then uses the DC gain at the collector current for the AC gain (in effect linearizing the gain, making it independent of the signal amplitude).

 

See

 

See
View attachment 302812

Thanks all!

 

hi RRRR,
Have you run that LTSpice simulation on your PC, if yes, please post your asc file.
E

 

I think you want to know voltage gain but the beta gain shown is current gain, not voltage gain.
Unless you change the specs of the transistor model, the transistor you use might have minimum or maximum specs which produce different results than the "typical" specs of the model.

 

I think you want to know voltage gain but the beta gain shown is current gain, not voltage gain.
Unless you change the specs of the transistor model, the transistor you use might have minimum or maximum specs which produce different results than the "typical" specs of the model.

I tried to run the sim but I can't get it to work.
I've done something wrong. When I try to run it the dialog box pops up.

 

Hi RR,
Have got the .dc dec set as a Comment?
E

 

The BF parameter of Spice is not the actual current gain. The proper name is "Beta Factor", and the description from the help page is "Ideal maximum forward beta". The implication is that the actual value of beta in a given circuit configuration has multiple inputs and parameter BF is only one of many. For more information you can Google:

"Gummel-Poon BJT model" and the number 1 hit will be the following Wikipedia article:

Gummel–Poon model - Wikipedia

 

Hi RR,
Have got the .dc dec set as a Comment?
E
View attachment 302836

Thanks EG. I need more coffee. Plot not right somehow.

 

The BF parameter of Spice is not the actual current gain. The proper name is "Beta Factor", and the description from the help page is "Ideal maximum forward beta". The implication is that the actual value of beta has multiple inpuf and parameter BF is only one of many. For more information you can Google:

"Gummel-Poon BJT model" an the number 1 hit will be the following wikipedia article:

Gummel–Poon model - Wikipedia

Thanks PB

 

Hi RRR,
Please post LTS asc file.
E

 

Hi RRR,
Please post LTS asc file.
E

Hi E
Here is the file.
RS

 

Hi RRR
This is what I see with a 2N2222A

E

 

Hi RRR
This is what I see with a 2N2222A

EView attachment 302853

Why does my plot differ? Could you pls attach your .asc file.

 

Why does my plot differ? Could you pls attach your .asc file. I don't have an "A"

 

hi RRR,
Look at this sim stepping BF
E

 

After calculation, the base current dependence ib(Q1) is obtained. Replace the axis with ic(Q1).

 

Hi RRR,
Open standard.bjt and insert the attached text.
You will have to close LTS and restart to get the My2N2222A active.
E