BJT transistor

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PsySc0rpi0n

Joined Mar 4, 2014
1,755
I included the picture that shows what I mean.
Ok, i have deleted the message because I need to try to understand better what you said before making that question, but now you answered so, I'll try ti understand what you said!


PS: And how can I calculate the Early Voltage with calculations?
 

shteii01

Joined Feb 19, 2010
4,644
Ok, i have deleted the message because I need to try to understand better what you said before making that question, but now you answered so, I'll try ti understand what you said!


PS: And how can I calculate the Early Voltage with calculations?
You have five plots. Each plot starts up then curves to the right and then continues to the right in a straight line. Get the two points on the straight line, using them find the equation of the line in the form of y=mx+b:
y is Ic
m is slope of the straight line
x is Vce
b is the point where straight line intercept Ic axis

Once you have equation of the straight line, set y=0 and solve for x. You will get some negative value. Drop the negative sign, keep the value, this value is the Early voltage. Just like my picture shows and explains in the text.

Just to double check. Do that for each plot. You have 5 plots, so you should have 5 calculations. They all should result in the same Early voltage value.
 
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ericgibbs

Joined Jan 29, 2010
18,766
Why do you choose 2N2222A? What is the interest of those points where you measured currents?
No particular reason for using a 2N2222A, I just edited an older sim.

What transistor parameter do you think measuring Collector current divided by the Base current will show.??
 

ericgibbs

Joined Jan 29, 2010
18,766
How can i use ".MEASURE" directive to check values of Y axis for at least 2 point on the X axis?
I would use the 'box' that appears on the plot window when you press and hold down the left mouse key.

Place the mouse cursor on the LEFT end of Ic, Ib plotted line that you want to measure.
[choose a point on the plot line that is crossed by a vertical Xaxis line, say 8V.]

Press and hold the left mouse key and expand the 'box' drawn by the cursor by dragging the Top Right corner onto the RIGHT end of the Ic, Ib plotted line.
[choose a point on the plot line that is crossed by a vertical Xaxis line, say 18V.]

EDIT: more detail
The 'box' that you expand will have its bottom left corner at say 8V on the plot line and the 'box' will have its top right corner at say 18V on the same plot line.

When you release the mouse button the plot will be magnified, to reset the plot click the 'anti clockwise' symbol shown in this image

Read the values on lower left Status bar, the data includes the slope of the line, OK.?
 

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Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
No particular reason for using a 2N2222A, I just edited an older sim.

What transistor parameter do you think measuring Collector current divided by the Base current will show.??
Will it be the Early Voltage?

I would use the 'box' that appears on the plot window when you press and hold down the left mouse key.

Place the mouse cursor on the LEFT end of Ic, Ib plotted line that you want to measure.
[choose a point on the plot line that is crossed by a vertical Xaxis line, say 8V.]

Press and hold the left mouse key and expand the 'box' drawn by the cursor by dragging the Top Right corner onto the RIGHT end of the Ic, Ib plotted line.
[choose a point on the plot line that is crossed by a vertical Xaxis line, say 18V.]

Read the values on lower left Status bar, the data includes the slope of the line, OK.?
If I understood, you're saying me to use the mouse to read values on the lower left corner of the status bar? That method can be a little inaccurate!

I would like to have accurate readings.
The method of clicking in the plot label and use the small window that shows up could be better, but it also depends on the precise spot LTSpice lets me stop the mouse.

Can't i use :MEASURE directive to give me accurate readings?

I have calculated the straight lines equations and the X value for Y=0 but they didn't were very close to each other.

I have calculated for 3 of the curves.

For the first curve next to 6 mA I used:
X1 = 4V and X2 = 16V
Y1 = 6.09mA and Y2 = 6.788mA

I got Ve = -100.636V

For the curve next to 18mA I used:

X1 = 4V and X2 = 16V
Y1 = 17.596mA and Y2 = 19.633mA

I got the Ve = -99.658V

For the last curve next to 27mA up to 33mA I used:

X1 = 4V and X2 = 16V
Y1 = 28.368mA and Y2 = 31.682mA

I got the Ve = -98.782V
 

ericgibbs

Joined Jan 29, 2010
18,766
Will it be the Early Voltage?
Not Early Voltage, think about current GAIN.:) Ib In, Ic Out

I will look at a .measure option, post back later.

EDIT:
This is a another example of .MEAS, its simple modification of the demo I posted earlier, you really should have been able to modify the .MEAS statement yourself..

Re-post your updated Early Voltage calculations.
 

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PsySc0rpi0n

Joined Mar 4, 2014
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What means the 3rd argument of .MEASURE, "tmp1" and "tmp2"???

PS: Is it just a label to what we are measuring?
 
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ericgibbs

Joined Jan 29, 2010
18,766
Ok, I have recalculated everything again and I got 3 V Early:

1 - -99.2981V
2 - -99.2703V
3 - -99.2572V
Were did you get the 3V from.??

[ dont forget ignore the minis sign]

Look at the LTS plots and visualise were all the plot lines will meet at the same point on the X axis... Its not 3V..:)

EDIT:
Look at this edited plot image. At what voltage do the lines meet at a point on the Xaxis.???
 

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PsySc0rpi0n

Joined Mar 4, 2014
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Sorry, i didn't explain myself well...

I have calculated only 3 Early Voltages... Not 3V...

And the 3 Early Voltages were those 3 values around [-]99V!!
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
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Now i have to reun a simulation with constant Vce of 10V and plot Ib(Vbe). Can you give a help on how to plot this correctly?

PS:

Would it be the attached file and image?
 

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Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
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That is is already done...

What you mean if I have a typo?

Now I have just done the first steps to the 2N3055.

Used a logaritmic scale to highlight the curve at the very beggining of the simulation!

There it goes...
 

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