High Brightness LED Zener Like Curve

[avincenty]

How do i do that? With a variable ccs?

 

[indianajo]

The only advantage I can think of in using this zener, instead of a real one, is that you need a 7 V zener, and you don't want to pay $6 freight to get one. I've been known to stack salvage 1n4148's on top of the 4 values of zeners I keep to make some other voltage.

 

[avincenty]

Can you test to see if the avalanche knee voltage is more current dependent than a regular zener?

Is this what you meant? The knee of the led in zener mode is not sharp, the true zener is very sharp. The graph below has been manipulated to match the terminal Zener voltage on the top right side of the curves, LED aprox 7.3 volts and Zener 6.2 volts. Current (Y) is at 100mv/ma

 

[sofaspud]

Looks like a pretty lame LED zener, perhaps due to the combination of reverse currents through the two PN junctions.

 

[danielwritesbac]

Is this what you meant? The knee of the led in zener mode is not sharp, the true zener is very sharp. The graph below has been manipulated to match the terminal Zener voltage on the top right side of the curves, LED aprox 7.3 volts and Zener 6.2 volts. Current (Y) is at 100mv/ma

Yes, excellent work there. But, that led probably shouldn't be run long term in reverse. There's no zener in there.

Other use:
The top of one of those leds can be sanded/filed flat, clear glued to a CDS and that thing painted black, and presto! handmade optocoupler. That can be used for my clipnipper or a really similar project from Rod Elliot. The settings can be different depending on which CDS is selected, but it is easily doable with parts from Radio Shack.

And, as a detector, the LED does not suddenly switch on and therefore I like the LED better for transparent compressors. Suddenly switch on with zener isn't transparent. But, after enough led's have been strung together for "gentle cushion" (approximately 3 for clipnipper), a zener can be added to the chain as needed to re-scale for more powerful amplifiers.

 

[avincenty]

Yes, excellent work there. But, that led probably shouldn't be run long term in reverse. There's no zener in there

Thanks.

This is where I am confused, isnt the built in ESD diode a zener?

I don't quite grasp how the non sharp knee is useful. Do you say running the device within the knee currents? On a regular scale the device looks like a regular zener like in my first post.

 

[sofaspud]

What does "regular scale" mean? What is your explanation for the difference in screenshots between post#1 and post#23?
The non-sharp knee may just mean that the LED zener is doped simply for LED protection, not for any sharp knee regulation-type function.

 

[avincenty]

In post 1 you see the full swing from a 6vrms ac drive, where you can see forward and reverse regions. Post 23 is only a zoom of the zener knee portion, see the grid scales,20mv on the x and 100mv/ma on the y.

 

[sofaspud]

Thanks, that's what I thought but wanted to be sure.

 

[avincenty]

This may be clearer

Left one is the LED connected in reverse.

 

[danielwritesbac]

Are both of those photos the led connected reverse?

 

[sofaspud]

That's my understanding. The left pic is the LED alone, the right pic zoomed into the reverse knee of the LED zener and regular zener.

 

[AndrewT]

post30:

are the voltage scales swapped between the two plots?
One goes -ve to +ve left to right
the other +ve to -ve left to right?

 

[avincenty]

No, same scales. The zoomed portion is the knee on the right hand side, current going up from zero.