Comments on: Which Resistor to Use with this LED?

By: Seeran Kunendran

Seeran Kunendran — Sun, 13 Mar 2016 17:41:27 +0000

Can someone help me to explain why at 20 to 30mA the line starts to curve for the luminous intensity Vs Forward current.

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By: Albert van Bemmelen

Albert van Bemmelen — Sun, 25 Oct 2015 06:58:52 +0000

Yes Robert, I noticed that too.
I previously also made my sentences shorter.
But I probably already wrote too much lenghtly sentences. Haha.

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By: Robert Calk

Robert Calk — Fri, 23 Oct 2015 14:16:17 +0000

P.S. For some reason this article is clipping the comments
short. That is why I'm making the sentences shorter.

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By: Robert Calk

Robert Calk — Fri, 23 Oct 2015 14:14:15 +0000

The Zen50 takes 3 measurements to find the slope resistance.
You can read the user manual at their website. I would
imagine that a LED operating with much higher Rslope will
burnout faster than one with a lower Rslope. I guess I will
build 2 circuits on a breadboard with the same LED's that are
also from the same batch. Then operate one at a current with
high Rslope(about 20ohms), and the other LED at a current that
has real low Rslope(about 1ohm), 24 hours a day. Then I'll see
which one burns out first. If a LED having high Rslope really
matters, there should be a big difference in their longevity.

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By: Albert van Bemmelen

Albert van Bemmelen — Fri, 23 Oct 2015 12:44:47 +0000

In reply to Robert Calk.

Hi Robert, I'm no expert either but from the Link you gave about the slope resistance information website I understood that it all depends how you take the information from the current / voltage curve of your component. And because the diode curve isn't lineair its steepness or vertical slope increases non-lineair with an increasing momentary Forward voltage value. If you only measure on one momentary point on that curve you measure the DC or Static Resistance. At a certain forward I value and V value. Suppose I is 1mA.
And if you instead of one point use a triangle to measure its steepness over a larger area of the rising curve, beginning in the exact same momentary point you are able to detect the average rising value given out delta I and delta V. Whereas both deltas represent the amount in which I and V have changed from beginning point to the last point on the curve. And that they call that the Dynamic Resistance. And there is another way of measuring and also by using a triangle. So it all depends how many values you take on that curve.

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By: Robert Calk

Robert Calk — Thu, 22 Oct 2015 14:36:34 +0000

Hi Albert,
I'm not sure - I'm learning myself. But what we do know
is that resistance = heat. So it seems to me that a diode,
especially a LED, that has a higher slope resistance will
also have higher internal heat. How much that really matters,
I'm not sure. I was hoping that someone who has formal
training in these matters would educate us.
I'm not a Zen50 salesman, but until I bought one, I had
never even heard of slope resistance, which is also called
dynamic or differential resistance. That's another problem:
slope resistance is called by so many different names that
it is hard to find information about it. But of course, an
LED would be more susceptible to internal heat than a zener
or normal diode would be.

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By: Albert van Bemmelen

Albert van Bemmelen — Thu, 22 Oct 2015 08:09:03 +0000

In reply to Albert van Bemmelen.

If I understand it correctly does your Zen50 tester give the DC or Static Resistance. Which is a momentary Resistance measured at a certain DC forward current value at a certain corresponding DC Voltage over a diode, led or an avalanche breakthrough conducting zenerdiode. But given that no component is ideal and even one peticular component produced in large quantities has a deviation often catagorized in Datasheet values between Max, Typical and Min values, they all do work. And it only is important to know what limits are given in order to keep your component healthy. And knowing the Static Resistance doesn't really help you in any way, I think.

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By: Albert van Bemmelen

Albert van Bemmelen — Thu, 22 Oct 2015 07:34:29 +0000

In reply to Robert Calk.

Thanks Robert, I will have a look. And see if it does make me decide to also buy a Zen50.

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By: Robert Calk

Robert Calk — Wed, 21 Oct 2015 19:24:35 +0000

To Albert and anyone that is interested, I found this
on a website that gives some insight into slope resistance,
(or dynamic/ differential resistance).
http://electronics.stackexchange.com/questions/97883/
resistance-of-a-semiconductor-diode

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By: Robert Calk

Robert Calk — Wed, 21 Oct 2015 01:00:28 +0000

Thanks Albert. Those look like good meters.
I have the M6013 myself. Maybe some viewers
can benefit from your list of meters.

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