Everyone lights up LEDs in their own way.

Which of these is better for lighting LEDs?

  • Conventional methods like CC, resistor, etc.

    Votes: 0 0.0%
  • It depends. How likely is someone to sue you for getting shocked?

    Votes: 0 0.0%

  • Total voters
    4

Thread Starter

-live wire-

Joined Dec 22, 2017
912
You know, everyone lights up LEDs in their own way. Here are some of the conventional ways. Some people use CC for accurate control that can adjust for temperature changes. Others just use a resistor and a constant voltage, which is simpler and is best suited for certain applications, especially with minimal power. But I am a little unique. I like to do this. It might not be too good for component life, but it is simple and it lights up pretty bright. And you can have very loose connections and it will arc to the LED. Extremely convenient!
https://photos.google.com/share/AF1QipPP0AG7qMdCGajA_CCGo5dTPWmUry5DGMcEzMbLfwV-0PiZarMeF7Vxtm0csHdAIw?key=SDN5aGE0ckNGajVVeFFMUTJ4MG15bzNOaG0tNkhR
It uses inductive spiking from a small rewound step up transformer. It is powered by a PS that goes into CC when there is overcurrent. It shocked me a few times, but it was not too much worse than bad static. I would take many more precautions if it was continuous or could supply more power. I will design a proper circuit for it soon.

Seriously though, could someone explain why this is happening, and why they actually work?
 

Papabravo

Joined Feb 24, 2006
14,237
Why what is happening? An LED is basically a current operated device. It responds to the instantaneous value of the current, and has a persistence effect which allows some level of luminous intensity after the instantaneous current decays. If you compute the integral of the instantaneous current over time you get some insight into what is happening. Is that what you were asking?

By the way, most normal folks light LEDs in the same simple way because doing it in exotic ways doesn't buy you very much.
 

Thread Starter

-live wire-

Joined Dec 22, 2017
912
Google the phrase "inductive kickback".
I understand how the HV is generated, and why it only happened when it was disconnected. I was asking about how the LED functions normally despite the huge momentary power through it. Especially when other semiconductor devices fail miserably under momentary overvoltages.
Why what is happening? An LED is basically a current operated device. It responds to the instantaneous value of the current, and has a persistence effect which allows some level of luminous intensity after the instantaneous current decays. If you compute the integral of the instantaneous current over time you get some insight into what is happening. Is that what you were asking?
Ok. I tested a one or two afterwards. What I noticed, at least in a few of them, is that the fV dropped substantially and it behaved like a resistor in the 10s of ohms afterwards. I actually just remembered that the ones I used had built in resistors. I guess the LED failed short but the resistor survived. So I am just wondering how it gets damaged so much, but then still emits a substantial amount of light. While some of them died, some seemed to continue to work under the HV. And in both polarities. But while they worked with the HV, they still failed to emit light in a usual setup with a resistor. This just seems pretty strange.
 

OBW0549

Joined Mar 2, 2015
3,506
I guess the LED failed short but the resistor survived. So I am just wondering how it gets damaged so much, but then still emits a substantial amount of light. While some of them died, some seemed to continue to work under the HV. And in both polarities. But while they worked with the HV, they still failed to emit light in a usual setup with a resistor. This just seems pretty strange.
You've left electronics behind, and are now playing around in the Voodoo Zone.

You zapped your LEDs. End of story.
 

Thread Starter

-live wire-

Joined Dec 22, 2017
912
You've left electronics behind, and are now playing around in the Voodoo Zone.

You zapped your LEDs. End of story.
You seriously abused the LED junction :eek:, so it's anyone's guess what happened to them.
Wow. I did not know this was so much of a taboo/mystery, zapping LEDs. But wait. I was zapped by it and I still work fine. While the LEDs frequently failed. So logically we should use people instead of LEDs as lights. :)
 

OBW0549

Joined Mar 2, 2015
3,506
Wow. I did not know this was so much of a taboo/mystery, zapping LEDs.
LEDs typically have very low reverse breakdown voltages compared to most silicon diodes and rectifiers; a Vr(max) specification of only 5 volts is common. Also, they tend to be very intolerant of reverse current and are sensitive to ESD (especially the blue and white ones). If you want them to last a long time, treat them with care and observe data sheet voltage/current limits.

If you don't care whether they last a long time, of course, just carry on.
 

Thread Starter

-live wire-

Joined Dec 22, 2017
912
Some more fun with HV. I made a fast charging port. Only works with the "lightning" charger though. :D
https://photos.google.com/share/AF1QipNjU59bWpSVPXkWqxDkvc7YNY8-yEr21uJZmlBZPWn9RK6td2KKXoebblXNuzbK-g?key=cGp0VlFjUWViUnFDdW00em9Jc2NUN3dRM1k2bW9n
I made a basic oscilator with a EM relay. Voltage rises, relay on and overcurrent, voltage collapses, relay turns off, normal voltage, relay closes again, and this repeats. The contacts got welded to each other many times. Percussion maintenance fixed that though. I could probably use a solid state relay or fet/IGBT but they do not seem to be as tolerant of overvoltages and overcurrents. I will build a real oscilator but I just needed something quick.

I actually created a dimmer with another one by varying the arc distance to the LED. It worked surprisingly well. Why would anyone consider PWM when you can just do that? ;)
 

RichardO

Joined May 4, 2013
2,271
I made a basic oscilator with a EM relay. Voltage rises, relay on and overcurrent, voltage collapses, relay turns off, normal voltage, relay closes again, and this repeats. The contacts got welded to each other many times. Percussion maintenance fixed that though.
For precision dithering, you need a calibrated hammer. :D
upload_2018-5-13_20-18-57.png
 
they tend to be very intolerant of reverse current and are sensitive to ESD (especially the blue and white ones)
It never even occurred to me! As far as i know i have never destroyed one with ESD, BUT that isnt a big surprise seeing as i generally try and take reasonable ESD steps in my workshop anyway, and i spent a fortune on the table ESD mat! (why does that stuff cost so much!).
I will however bare it in mind in the future! I tend to use tiny smd leds these days so ESD tweezers are pretty standard as i got sick and tired of soldering my finger tips
 

Thread Starter

-live wire-

Joined Dec 22, 2017
912
Esd stuff is just conductive materials to provide a better discharge path not through sensitive stuff, right? Or is it something else?
 

OBW0549

Joined Mar 2, 2015
3,506
Esd stuff is just conductive materials to provide a better discharge path not through sensitive stuff, right? Or is it something else?
Yup. ESD mats, wrist straps, etc. provide a path to ground, usually through a fairly high resistance like a megohm or more, to bleed off any static charge without causing a spark.
 
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