# LED I-V Characteristics

Discussion in 'General Electronics Chat' started by Hurt_it_Circuit, Oct 26, 2012.

1. ### Hurt_it_Circuit Thread Starter Member

Oct 2, 2012
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why does an LED I-V curve look exponential? What causes this? How would one compare a measured graph to a theoretical LED I-V curve?

Apr 5, 2008
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3. ### bountyhunter Well-Known Member

Sep 7, 2009
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because it's a diode?

4. ### spinnaker AAC Fanatic!

Oct 29, 2009
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So that's what the D stands for in LED. Who knew?

5. ### Austin Clark Active Member

Dec 28, 2011
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Precisely. Many components don't have a straight, or linear, I-V characteristic. Physically, as the voltage across a PN junction (a diode) increases, the "depletion region" between the PN junction shrinks, leading to, effectively, lower resistance overall. I like to look at it as though resistance decreases with voltage, so the current increases exponentially with voltage. I'll probably be yelled at for saying that, but it works for me.

6. ### cabraham Active Member

Oct 29, 2011
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Well, incrementally, I would agree that small signal ac resistance increases as the diode is biased upward on the I-V curve. But re "resistance" in the general sense, I don't think I agree with you.

Claude

7. ### crutschow Expert

Mar 14, 2008
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LEDs and diodes are classified as non-ohmic or non-linear, but they still have resistance to a DC current flow and dissipate power as determined by V * I at their operating point. They have a non-linear resistance.

Last edited: Nov 1, 2012
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8. ### cabraham Active Member

Oct 29, 2011
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Of course, I was just saying that you cannot regard diode "resistance" the same as in the general Ohmic sense. It is non-linear, & varies with I-V operating point, as well as temperature. An equation or graph is needed to understand the device fully, as the simple R = V/I relation does not hold.

Claude

9. ### Ron H AAC Fanatic!

Apr 14, 2005
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I think you meant "decreases".

10. ### cabraham Active Member

Oct 29, 2011
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Yes I did mean to say decrease. Sorry if I led anybody astray. As dc bias I-V point increases, incremental resistance decreases.

Claude

11. ### ramancini8 Member

Jul 18, 2012
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Of course none of this applies to the DED released by Fairchild Semi about 40 years ago around April 1.

12. ### Ron H AAC Fanatic!

Apr 14, 2005
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They also developed a version called the DEAD. The yield on both of these was said to be fantastic.

13. ### crutschow Expert

Mar 14, 2008
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But they sure took a lot of current to achieve a reasonable light output.

14. ### Ron H AAC Fanatic!

Apr 14, 2005
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It was brief, but spectacular.