# Homework Help: Turn-on voltage from I-V graph

1. May 5, 2012

### harryexe

How do we determine the turn-on voltage from a given I-V graph?

2. I have attached the picture. The graph which i need to obtain the turn-on voltage from is on the right.

3. I have searched the web and the closest answer I can find is from this website (link can't be posted due to lack of post) It says that "One method to consider begins with plotting the I–V data on a semi-log graph. Your
data should approximate a straight line, indicative of the exponential nature of the current
voltage relationship. An operational deﬁnition of the threshold voltage could be that value
of the bias voltage when the current reaches 0.01 mA. Extrapolate your I–V curves to where
they cross 0.01 mA current and use that as the working value of V0." However, during the briefing prior to doing the experiment and obtaining my data, the professor told find a gradient at one point of the curve and find the point where it intercept the x-axis (the voltage) which will give me the turn on voltage. No semi-log graph is needed here. But which point from the graph do i find the get the gradient to extrapolate? Thank you!!!!

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2. May 7, 2012

### Staff: Mentor

Hi harryexe. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]
Are we to assume this is for a diode?

I don't believe your 1.8MB attachment conveys any more information than would something of more reasonable size, such as 300KB. As a courtesy to readers, would you make sure that future attachments are of a less extravagent size? Most paint/photo programs allow you to save to a smaller size.
Turn-on voltage has no one universal definition. I'm afraid you are going to have to abide by the instructions you have been given, if you wish to satisfy the requirements of that person who will be marking your work. Turn-on voltage is not usually regarded as a precise parameter.

Last edited by a moderator: May 6, 2017
3. May 9, 2012

### harryexe

Thank you for your reply =] In addition, what exactly are the factors affecting the turn-on voltage?

4. May 12, 2012

### Staff: Mentor

Look up the "diode equation".