How Do We Find Turn-On Voltage from an I-V Graph?

[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!

 

[NascentOxygen]

Hi harryexe. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

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

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.

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!

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.

 

[harryexe]

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

 

[gneill]

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

Look up the "diode equation".

 

[DeeNos]

I would say that there are multiple methods to determine the turn-on voltage from a given I-V graph, and the most appropriate method may depend on the specific nature of the data and the desired level of accuracy. One method, as mentioned in the website you found, is to plot the data on a semi-log graph and extrapolate the curve to where it intersects with a certain current value, such as 0.01 mA. This can give a good estimate of the turn-on voltage.

However, your professor's method of finding the gradient at a specific point and extrapolating to the x-axis is also a valid approach. The specific point at which to find the gradient may depend on the shape of the curve and the desired level of accuracy. It is important to note that both methods rely on extrapolation, which means that the calculated turn-on voltage may not be entirely accurate. Therefore, it is always important to consider the limitations of the data and the chosen method when determining the turn-on voltage from an I-V graph.