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?

 

Hello,

Have a look at the pages 31 and 32 of the following PDF:
LED's

This is a PDF from the following page of the EDUCYPEDIA:
http://educypedia.karadimov.info/electronics/composemiconductorsled.htm

Bertus

 

why does an LED I-V curve look exponential?

because it's a diode?

 

because it's a diode?

So that's what the D stands for in LED. Who knew?

 

because it's a diode?

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.

 

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.

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

 

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.

 

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. The have a non-linear resistance.

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

 

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

I think you meant "decreases".

 

I think you meant "decreases".

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

Claude

 

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

 

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

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

 

But they sure took a lot of current to achieve a reasonable light output.

 

But they sure took a lot of current to achieve a reasonable light output.

It was brief, but spectacular.