BJT transistor

ericgibbs

Joined Jan 29, 2010
18,766
When plotting Ic(Vce) for 2N3055, the Early Voltage is 0????


How can that be correct.??


CLUE
: The Ic(Q1) plots converge on the Yaxis Zero line....

Remember the formula for a straight line, y = mx + c , then make y =0
 
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ericgibbs

Joined Jan 29, 2010
18,766
As you can see at my #36 post, the values from directive .MEASURE gives me a slope of zero.

And yes, I'm using Y = mX + b
hi Psy,

Why have we jumped back to post #36 for the 2N3055.???
It gives an apparent slope of zero because the Ib increments are to large.

Ref the 2N2907 look at this sim plot, what do you think the Early Voltage is now.??

EDIT:
Re-Checked the #36 asc, I suspect that the LTS 2N3055 Model has limitations.??
 

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PsySc0rpi0n

Joined Mar 4, 2014
1,755
ericgibbs, we are making a big mess here... lol...

I'm simulating the 2N3055 right now to check it's Early Voltage.

And the curves are like the ones i have in #36 post which gives a slope of 0.

Our teacher asked us to repeat the simulation we did for the first bjt but with a Vce voltage going from 0 up to 30V in 0.1 steps...

I gt those curves...
 
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PsySc0rpi0n

Joined Mar 4, 2014
1,755
hi Psy,

Why have we jumped back to post #36 for the 2N3055.???
It gives an apparent slope of zero because the Ib increments are to large.

Ref the 2N2907 look at this sim plot, what do you think the Early Voltage is now.??

EDIT:
Re-Checked the #36 asc, I suspect that the LTS 2N3055 Model has limitations.??
What you mean "have limitations"???
 

ericgibbs

Joined Jan 29, 2010
18,766
What you mean "have limitations"???
I suspect that the 2N3055 model is not detailed enough to calculate the small changes in Ic for small changes in Ib ie: the resolution of the model is too coarse.?

E

EDIT:

For a test I have used the 2N3055H model, this is better !!

The other 2N3055 model is no good!! IMO

Added .MEAS for x3y3
 

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PsySc0rpi0n

Joined Mar 4, 2014
1,755
Thanks for the help... I'm going to replace my simulations with that one and recalculate Early Voltage!

Can you provide full model for 2N3055H so that i can add it to LTSpice?


Edit;

I got it... Thanks
 
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ericgibbs

Joined Jan 29, 2010
18,766
Thanks for the help... I'm going to replace my simulations with that one and recalculate Early Voltage!

Can you provide full model for 2N3055H so that i can add it to LTSpice?
The 2N3055H should already be part of your transistor library, let me know if you cannot find it.

Here it is, paste it ALL in the standard.bjt in the lib/cmp folder

.MODEL 2N3055H NPN(IS=2.37426e-14 BF=129.119 NF=0.85 VAF=31.1252 IKF=0.990922 ISE=2.47498e-10 NE=1.89002 BR=1.01252 NR=0.924456 VAR=254.624 IKR=2.70227 ISC=2.47498e-10 NC=2.90624 RB=3.66609 IRB=0.1 RBM=0.1 RE=0.000352673 RC=0.0764459 XTB=1.34801 XTI=1.07207 EG=1.206 CJE=9.03089e-08 VJE=0.513954 MJE=0.59999 TF=1e-08 XTF=1.36696 VTF=1.02605 ITF=0.987296 CJC=5e-10 VJC=0.400243 MJC=0.410238 XCJC=0.803124 FC=0.661216 CJS=0 VJS=0.75 MJS=0.5 TR=1e-07 PTF=0 KF=0 AF=1 VCEO=60 ICRATING=15 MFG=Motorola)
 

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PsySc0rpi0n

Joined Mar 4, 2014
1,755
ericgibbs, what can we say about 2N3055H regarding the big difference of Early Volt comparing with 2N2222??? Is it because of different Ic? What makes the Early Volt to change?
 
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Jony130

Joined Feb 17, 2009
5,487
ericgibbs, what can we say about 2N3055H regarding the big difference of Early Volt comparing with 2N2222??? Is it because of different Ic? What makes the Early Volt to change?
Transistors don't have the same Early Volt. So I don't understand your question. 2N3055 is a high power transistor, and this is why it has different properties then 2N2222.
As you can see
.MODEL 2N3055H NPN(IS=2.37426e-14 BF=129.119 NF=0.85 VAF=31.1252 IKF=0.990922 ISE=2.47498e-10 NE=1.89002 BR=1.01252 NR=0.924456 VAR=254.624 IKR=2.70227 ISC=2.47498e-10 NC=2.90624 RB=3.66609 IRB=0.1 RBM=0.1 RE=0.000352673 RC=0.0764459 XTB=1.34801 XTI=1.07207 EG=1.206 CJE=9.03089e-08 VJE=0.513954 MJE=0.59999 TF=1e-08 XTF=1.36696 VTF=1.02605 ITF=0.987296 CJC=5e-10 VJC=0.400243 MJC=0.410238 XCJC=0.803124 FC=0.661216 CJS=0 VJS=0.75 MJS=0.5 TR=1e-07 PTF=0 KF=0 AF=1 VCEO=60 ICRATING=15 MFG=Motorola)
Model specifies Early Volt = VFA = 31.1252V

And for 2N2222 VFA = 100V
 

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PsySc0rpi0n

Joined Mar 4, 2014
1,755
I need to justify the differences...

But I think i sorted it out already... I said that as each bjt has it's own β, and that β depends on Ic and Ib, the Vfa would change when different β were put to the test!
 

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PsySc0rpi0n

Joined Mar 4, 2014
1,755
What can I say about the differences to 2N2907 that as the curves upside down?

Does it has anything to do with different polarization?
Can you help me to explain why does this BJT has it's curves upside down?
 

ericgibbs

Joined Jan 29, 2010
18,766
Can you help me to explain why does this BJT has it's curves upside down?
hi,
The curves are not upside down.:)

The X axis intersects the Y axis when Y =0 for the LTS plots.

Values of Y above the Y=0 axis and to the right of the X=0 are considered positive values of Y.

Values of Y below the Y=0 axis and to the right of the X=0 axis are considered negative values of Y.

Look up the standard 4 quadrant representation for maths and graph plots, for the other two quadrants

As a budding engineer, its very important that you fully understand the 4 quadrant numerical maths polarity definitions.

http://www.studyzone.org/mtestprep/math8/e/fourquadrant6l.cfm

E
 

ericgibbs

Joined Jan 29, 2010
18,766
hi,
If you prefer to show the 2N2907 Ic plot versus negative values of Vce you can force LTS to show it that way.

image02 is plotting Vce * -1 on the X axis, this is the method I prefer, its in the correct quadrant.

image03 has Vce plotted on the left side Y axis and the Ic scale on the right side Y axis, ignore the X axis values.
 

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PsySc0rpi0n

Joined Mar 4, 2014
1,755
But is the plot correct like it is???? Are both power sources correctly placed in the circuit? It's just that I need to know!

I'm going to read the last link you posted!
 

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PsySc0rpi0n

Joined Mar 4, 2014
1,755
ericgibbs, that link teaches how to read values on a grid? Come on... I thought it was something else... I know how to read values on a grid...

But in that plot I have the curves upside down with negative values for Ic. The curves are like mirrored in the X axis comparing with the previous BJT!
 
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