Why Are My Diode IV Characteristics Readings Different?

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Discussion Overview

The discussion revolves around the discrepancies observed in the IV characteristics readings of a diode during an experimental setup. Participants explore potential reasons for the differences in voltage readings corresponding to diode current when varying the resistor in the circuit.

Discussion Character

  • Experimental/applied

Main Points Raised

  • One participant notes that the expectation is for the readings to be consistent but questions whether the measurements were accurately compared, suggesting a possible mix-up in current readings.
  • Another participant challenges the assumption of zero resistance for the ammeter and infinite resistance for the voltmeter, indicating that real-world meters have finite resistances that could affect the measurements.
  • A further suggestion is made to provide additional details about the components used in the experiment, including the type of diode, meters, voltage supply, and the range of currents tested, to better diagnose the issue.
  • One participant raises a concern about the correctness of circuit connections, proposing that the voltage might be measured across the resistor instead of the diode.

Areas of Agreement / Disagreement

Participants express differing views on the accuracy of the measurements and the assumptions about the meter resistances. There is no consensus on the cause of the discrepancies, and multiple potential explanations are presented.

Contextual Notes

Limitations include the lack of specific details about the experimental setup, such as the values of the resistors used and the characteristics of the measuring instruments, which may be crucial for understanding the observed differences.

user20161768
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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.
 
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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.
 
user20161768 said:
... 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!
 
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I wonder if your circuit connections are correct. It sounds as if you are measuring voltage across the resistor rather than across the diode.
 

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