# Next report - BJT polarization

#### ericgibbs

Joined Jan 29, 2010
9,386
But shouldn't this kind of polarization parameter change proof??? Wasn't it supposed to respond the same way when parameters change?
This circuit configuration does compensate for changes, but you are forcing a Base current of 38uA.! Do not mix divider Base biasing and a fixed current source.

The biasing resistor divider and the emitter resistor are normally used in this type of circuit, no fixed current source.

Try your sims without the current source.

#### PsySc0rpi0n

Joined Mar 4, 2014
1,446
hi,
The Base current on the last circuit is set to 36.63uA and the other two circuits its only 14.66uA, they will be very different.

The resistor divider chain on the Base has NO effect on the Base current.

You could just connect the left side of the Ib current source to Common/0V.!
Hum, my mistake in the uploaded files!
Going to upload them again in the other post!

#### PsySc0rpi0n

Joined Mar 4, 2014
1,446
I think files are ok now... By the names you can figure out which one is normal, beta = 100 and temp = 100.

The normal and beta = 100 produces similar Ic(Vce) curves but the temp = 100ºC is a bit more faraway from the 2 first simulations.

You said that because of Ib change, the plot would also change, but the 2 first sims has different Ibs and they are very similar.
I was hoping to get the same from the temp = 100 plot!

#### ericgibbs

Joined Jan 29, 2010
9,386
This is what I get.

Use .param temp 100

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#### PsySc0rpi0n

Joined Mar 4, 2014
1,446
This is what I get.

Use .param temp 100
So the directive I have is wrong?

I did like:

Rich (BB code):
.temp 100

#### ericgibbs

Joined Jan 29, 2010
9,386
So the directive I have is wrong?

I did like:

Rich (BB code):
.temp 100

I am getting an unexpected result, little puzzling,will check it out.

EDIT:

Ran the Temp from 20 to 100C is 10C steps as a check of .temp 100
The top plot is at 100C
Its what I would expect for the way the Base current has been fixed.

You should decide which transistor parameter you want to plot and the method used to provide the Base current.
Its getting a little confused in the way your circuits are configured.

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Last edited:

#### PsySc0rpi0n

Joined Mar 4, 2014
1,446
The method has been always the same.

Simulate the circuit as it is, then change β to 100 and simulate and last is to change temp to 100ºC and simulate again.

When I change the β to 100, I recalculate Ib for that β and run the simulation.
Then I just change temp to 100ºC and sun simulation. So i have 3 curves.

Then I have to overlay those 3 curves and draw the Load Line.

#### PsySc0rpi0n

Joined Mar 4, 2014
1,446
Well, I have finished the report... Now I'm going for the lab part of the work!

#### ericgibbs

Joined Jan 29, 2010
9,386
Well, I have finished the report... Now I'm going for the lab part of the work!
Hi,
I hope the report goes well.
E

#### PsySc0rpi0n

Joined Mar 4, 2014
1,446
Hi,
I hope the report goes well.
E
I can send it to you if you want to take a sneak peak at least to see the screens and calculations!

#### ericgibbs

Joined Jan 29, 2010
9,386
I can send it to you if you want to take a sneak peak at least to see the screens and calculations!
Hi,
I am sure many fellow students would find reading your Report useful.
E

#### PsySc0rpi0n

Joined Mar 4, 2014
1,446
Hi,
I am sure many fellow students would find reading your Report useful.
E
I was just telling that i can send it to you just to look for the screens and calculations as it is written in portuguese, so maybe not of big interest sending it here to forum.

#### JoeJester

Joined Apr 26, 2005
4,134
If you use the ideal transistor with all the default parameters, changing just the bf will produce the desired results.