Why Are My Diode IV Characteristics Readings Different?

[user20161768]

I was doing an experiment to plot the IV characteristics of a diode. I connected a resistor, diode and milli ammeter in series. I connected a voltmeter across the diode. I measured the diode voltage and diode current. When i changed the resistor, I got a different set of diode voltage readings for the corresponding diode current. Why are the readings different?

Before I changed the resistor, i waited for 15 mins to allow the diode to cool back to normal temperature. The ammeter resistance is 0 and voltmeter resistance is infinite.

 

[Averagesupernova]

Interesting. I would think they would be the same. Are you sure you weren't comparing 50 mA to 500 mA or something? Could be easy to do depending on your meter.

 

[Merlin3189]

... The ammeter resistance is 0 and voltmeter resistance is infinite.

Well there's one factor, because your ammeter will not be zero resistance and your voltmeter will not be infinite. You'd like them to be, but they can't be perfect. *
Typically an electronic voltmeter is about 10MΩ and your milliammeter maybe 1Ω.

Without knowing the details of what size resistors and what meters you were using, it's hard to say whether this was the cause of your error. Perhaps you could give details? What diode, what meters, what voltage supply, what range of currents you tested and which test gave you the problematic results.

Edit: * Unless you mean you are using simulation software, rather than doing a real experiment!

 

[tech99]

I wonder if your circuit connections are correct. It sounds as if you are measuring voltage across the resistor rather than across the diode.