Wrong - Theory,LED or Mains

[gmphadte]

I am surprised to see some constructive comments as I was biased for the worst.

The pictures will be posted later but these r some more things I tried yesterday and today first thing in the morning.

I was not lucky as I powered 10 LEDs of 4 types. One is an IR.

Mr. PJP wrote

Why don't you connect two LEDs in series, in reverse ? If they both light up, that will prove that the LED is in reverse breakdown.

Anyway, I don't understand what you are trying to prove. What you are doing is definitely unsafe and unwise. Just because you did it and got away with it doesn't mean everyone should start doing it.

This was a very sarcastic, I am Mr. RIGHT comment.
This is a big volley returning to u

Yes, I thought of it and said what if the reverse leakage current drives the forward biased LED.

It does and both the LEDs r lighting.
Your sarcasm led to a new and innovative schematic in which the LEDs will last much longer.

ENJOY

 

[pjp]

I was trying to be helpful.

 

[gmphadte]

Out of curiosity, I looked into the issue.

A book I have a plot showing the leakage current starts around 5V for a red GaP LED. The current increases exponential to the voltage and the increase is slower than true Zener diodes. The voltage varies a lot within a lot by samples so picking an LED to substitute a Zener isn't a good idea.

The destruction of LED comes from the over current not from the over voltage, as others stated already, and ~2 mA seems fine for your LEDs.

What happens is that the brightness of LED degrade down faster, compared to normal usage. There are many papers on this issue but recent example is:

Defect generation in InGaN/GaN light-emitting diodes
under forward and reverse electrical stresses
X.A. Cao *, P.M. Sandvik, S.F. LeBoeuf, S.D. Arthur
Microelectronics Reliability 43 (2003) 1987–1991

which demonstrates slow degradation of the LED but mainly in the low current region. The authors suggest that the reverse voltage causes some physical change which leads to final defect eventually. There were almost no noticeable difference in the current-brightness plot at higher current region with reverse bias stress.

Dear Gajanan, do you have a reference to the description of the "theory" you disproved? I couldn't find a reference saying that a red ~ yellow LED would fail immediately if a reverse current of 2 mA was applied.

Please let me know for mistakes I made here. All the criticisms are welcome!

Best regards,
Satoru

Thanks for your explanation. I didn't refer to anything.
Your explanation brings out a newer overview, long ignored by few/many.

EDIT:Now, there is no surprise that a 100K also is good enough.

 

[Bonsai]

Good. Now we know for certain that good engineering demands we protect the LED (any LED) from reverse bias.

 

[ostripper]

Anyway, I don't understand what you are trying to prove. What you are doing is definitely unsafe and unwise. Just because you did it and got away with it doesn't mean everyone should start doing it.

The corporations do this for LED Xmas lights ... a fuse then a single diode , then 25-50 cheap forward biased LED's. all running off of 120vAC. At least a little
engineering was involved.

Ones below have been on for 2 years on my front porch (smoking room).
OS

 

[CBS240]

Same old song! How people is afraid around the world!

I think the point from Bonsai was more tuned to the fact that that we do not discuss non-isolated mains circuits on this WW public forum because generally not everybody reading understands that if mains gets a hold of you, the voltage will not drop, but rather the current can potentially flow through your body to earth ground and kill you. Most equipment cases are at earth gnd. A transformer isolates the live current from earth ground so you (and anyone else that contacts your circuit) does not get electrocuted, especially where mains is 240V. Threads around here pertaining to people 'playing' with non-isolated mains circuitry usually end up closed, and for good reason.

 

[ostripper]

Same old song! How people is afraid around the world!

I have been "Bit" by both 120 and 240 mains and if it was not for my very quick reflexes , I would not be here.

It really is irresponsible to suggest "playing" with the mains. My amp at 155v rail potential would KILL me instantly (deadly DC) reflexes would be damned.

I am not afraid , just want to live to build more amps. 😀
OS

 

[gmphadte]

If u say little engineering was involved, I would say too good engineering was involved in the neutron atom combo.

And by the way, diode in series has nothing to do with safety.

And as Satoru pointed out, the LED would not mind the high reverse voltage.
Only our prejudices get hurt.

Gajanan Phadte

 

[DF96]

I thought Saturo pointed out that, as I and others suspected, the reverse current will shorten the life of the LED?

This thread started silly, then got worse. I am bowing out.

 

[smartx21]

Problem with links

There are many papers on this issue but recent example is:

Defect generation in InGaN/GaN light-emitting diodes
under forward and reverse electrical stresses
X.A. Cao *, P.M. Sandvik, S.F. LeBoeuf, S.D. Arthur
Microelectronics Reliability 43 (2003) 1987–1991

Hi, Satoru,
There is some problem in the way you attached those links.
Could you redo that, please? Thanks.
Max.

 

[satoru]

Hi, Satoru,
There is some problem in the way you attached those links.
Could you redo that, please? Thanks.
Max.

Hi,

I didn't attach the paper itself. Only the title, author and journal. Please drop me a PM if you want a copy!

The reverse bias used in the paper was -20V. Of course, too high reverse voltage will kill an LED if there is no current limit.
By the way, I found descriptions stating that a "reverse biased LED with current limiter can be a good noise source". I tried to find the reference but couldn't within limited time I spent but there was a news group thread on the issue in which the poster seeking an advice since his circuit wasn't working. A reply from Win Hill (the author of "The Art of Electronics" who is quite active on electronics news groups) was to crank up the current higher than 2 mA or even try with 20 mA! So, certainly, some type of LED can survive and serve peculiar purposes with 2~4 mA reverse current.

Yes, reverse current/voltage will shorten the life of LED but it looks like that the mechanism of it is not fully understood yet.

I stayed away from the issue of the mains in the original post. Simply because I don't have enough experience with mains (I'm a low power guy and all my amps are battery operated 🙂 and people already made points on the safety in that regard.

Best regards,
Satoru