Hi, i am a first year student and i got an assignment : to make 2 I/V graphs and compare between them,
one of silicon diode 1N4003 and the other one schottky diode SR5200, with Tj=25 C. by using their datasheet.
can someone help me? where in the datasheet should i look and how to i use the Tj = 25C.

 

Have you looked at the data sheet for either one?

 

yes i looked at the datasheet and i saw some charts for Tj = 25C, but i dont understand what should i take from them to calculate V/I .

 

yes i looked at the datasheet and i saw some charts for Tj = 25C, but i dont understand what should i take from them to calculate V/I .

Did you see a chart that gives the forward current on one axis and the forward voltage on the other?

 

for the diode 1N4003 i saw 2 graphs one forward and one reverse, in the datasheet of the schottky not exactly current and voltage/

 

this is the graphs that i see.

 

Do you know what an I/V graph is?
It's voltage vs. current, and I see one graph in each of your attachments showing that.

If you want to compare then, you could plot the difference in voltage between them vs. current.

 

yes i know but i was asked to make my own graph and not copy the one from the datasheet.

 

yes i know but i was asked to make my own graph and not copy the one from the datasheet.

I think you misunderstood.
Since you already have that information in graphs I know of no way to generate them independently, since that's the only information in the data sheet that quantifies that.
It makes no sense to try to generate the graphs some other way.

I think the appropriate way to compare them is to plot their difference in voltage versus current.
I think that's the point your instructor was trying to make.

 

but there should be some equation that consist the (Tj,Vd,Id) , that you can calculate (put different V and find what I youll get) or am i wrong?
he asked to make the graphs in excel so i dont think he wanted me to copy the graphs.

 

i am a first year student and i got an assignment : to make 2 I/V graphs and compare between them,
one of silicon diode 1N4003 and the other one schottky diode SR5200, with Tj=25 C. by using their datasheet.

i dont think he wanted me to copy the graphs

From your original post, my first impression was that you were being asked to create the IV graphs as a lab exercise, i.e. experimentally.

Unless you have a way to cool the device and maintain a constant temperature, you can't control the junction temperature. A datasheet will tell you thermal resistances are so you can convert Ta to Tj.

 

Since you are specifically told to use the data sheets for specific, real diodes, you should use the data for those diodes contained in those datasheets.

Take the data from the I-V curves in the data sheet for a number of points and enter those into your Excel spreadsheet. Plot both curves on the same set of axes. Making another plot showing the voltage difference as a function of current would probably also provide a useful graphic for your comparison.

You might also try to curve fit the diode equation to your data as best you can. You will probably see that it deviates significantly for higher currents. You might try to speculate on why that might be the case.

Remember, the heart of the assignment isn't the graph -- its the discussion comparing the two diodes. The plots are just to help you see what comparisons are worth making and to help you communicate them to your audience.

 

okay, i would try to take points from the graphs and get them in excel as close as possible. thank you for your help.

 

Hello,

What is strange is that you say that you are to use the data sheet but then you say that you have to create your own curves. This could lead to several different scenarios.

First would be that maybe you just have to plot the same two curves in ONE graph so that the comparison is more obvious.

Second would be you find one point on the data sheet written numerically (not a graph) and use that point to calculate the curve using the diode equation.

Third, you might extract the main three parameters from the curves and thus create your own curves using the diode equation with those extracted parameters.

If you had some example it would tell us which way they want you to do it. Since you mentioned an "equation" i thought that maybe they want you to find parameters and the use that equation to plot two curves.

If you have more information you can mention that now.

 

Hello,

What is strange is that you say that you are to use the data sheet but then you say that you have to create your own curves. This could lead to several different scenarios.

First would be that maybe you just have to plot the same two curves in ONE graph so that the comparison is more obvious.

Second would be you find one point on the data sheet written numerically (not a graph) and use that point to calculate the curve using the diode equation.

Third, you might extract the main three parameters from the curves and thus create your own curves using the diode equation with those extracted parameters.

If you had some example it would tell us which way they want you to do it. Since you mentioned an "equation" i thought that maybe they want you to find parameters and the use that equation to plot two curves.

If you have more information you can mention that now.

i thought to use the equation (from wikipedia) and build graphs of my own.

I is the diode current,
IS is the reverse bias saturation current (or scale current),
VD is the voltage across the diode,
VT is the thermal voltage kT/q (Boltzmann constant times temperature divided by electron charge), and
n is the ideality factor, also known as the quality factor or sometimes emission coefficient.

I and V are the ones ill choose by myself , VT i think i have to use the Tj that was given. now about the n , n=1 because i need a silicon diode and Is(I saturation maybe?) i thought i have to get it from the datasheet because they should be different in each diode, but i cant find Is in the datasheet maybe it has other name or symbol that i dont know.

 

Hi again,

kT/q is often taken to just be 0.026, but you can calculate it out if you want to and use 25 deg C (converted into Kelvin first) as the junction temperature if that's what you want.

Your best bet is to look up a spice model for each diode and just take N,Is,Rs, from there. That would be easier. BTW you need Rs too if you want to get close to real.

 

i thought to use the equation (from wikipedia) and build graphs of my own.

Why? Is that part of the assignment?

If not, consider that you are asked to compare the I-V curves for two, specific, real, physical diodes using the data sheets, each of which contains the typical I-V curves for that diode.

If you asked me to compare the acceleration rates for two specific car models and you provided me with plots of the actual acceleration rates for each, would you want me to come up with an idealized approximation to those curves and compare those, or would you want me to do what you asked me to do and that is to compare the acceleration rates for those two specific models of car.