# ultra low voltage LED?



## lazerlover

Was wondering if any of you guys knew of a compact LED that could be powered by 0.5V, and 600mA.

Many Thanks


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## space

Today (at least to my knowledge) there is no led that will produce visible (to the human eye) light at such low voltage. One could probably make a led that will work on that voltage, but the emitted light will have a wavelength far bigger than what we can see. "Normal" IR-LEDs start conducting at about 1.0V. 
What you probably could do is convert the 0.8V and 600mA to 3V and 15mA. Then you need a ultra low voltage step-up converter. Not the easiest job.


space


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## Cmd_Bash

i feel i should inform you that an LED (which is an acronym for light emitting diode) is baisically a modifed version of a regular diode, and regular silicon diodes require a minimum forward voltage of approximitly 0.7V. and on a second note, the voltage required to produce light in a LED is largly based on the wavelength (or color) that it is designed to produce. so if you want a low voltage LED you might be able to find LEDs that glow red for somwehere between 1.2V-1.6V but you'll be hard pressed to find an LED that cast of light at less voltage then that. if there's a particular use that you want to this light for, such as an indicator light or somthing, just let us know and we'll try to help you out


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## Cmd_Bash

deleted


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## TigerhawkT3

You could try adding a Joule Thief (works down to a third of a volt, apparently).


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## Jarl

yeah, but the efficiency is horrible for that


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## DM51

I have closed your other (identical) thread in the Batteries section. Please do not cross-post again - it is against the rules and it just causes confusion.


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## Black Rose

How about a merge of the threads?

All of the posts in the other thread are from folks that didn't post in this thread.


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## Black Rose

Cmd_Bash said:


> so if you want a low voltage LED you might be able to find LEDs that glow red for somwehere between 1.2V-1.6V


I received some 1000-1500 MCD 5mm Red LED Emitters from DX yesterday and they would not light up with a 1.5V button cell.

I had to use a 3V CR2016 to get them to light up, so those ones won't meet the original posters needs (if he wanted red LEDs).


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## TMorita

Black Rose said:


> I received some 1000-1500 MCD 5mm Red LED Emitters from DX yesterday and they would not light up with a 1.5V button cell.
> 
> I had to use a 3V CR2016 to get them to light up, so those ones won't meet the original posters needs (if he wanted red LEDs).


 
The forward voltage of a red LED is around 1.7 - 1.8 volts, so of course it will not light on 1.5 volts.

If you have a ten foot wall and you have a pole vaulter that can pole vault nine foot walls, he will not be able to pole vault over the ten foot wall. It's not like he will be able to pole vault over the wall only nine-tenths of the time, or maybe only nine-tenths of him goes over the wall. No, he smacks into the wall every single time, and doesn't get across.

Toshi


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## Oznog

Yeah, well, there still ain't no LED that can operate off 0.5v. 

And even though a red LED might light at 1.8v, ~2v is needed to actually run it at rated power.

The Joule Thief is not necessarily "inefficient". May not matter if he has a 600mA supply. There are other DC/DC converter ideas too. In fact a PIC can be used to build a supply IF there's a backup battery like a coin cell to bootstrap the Vdd line, then it can run a converter from there on a 0.5v source to not only power the load but its own Vdd current. 

But this may or may not make sense... a coin cell alone could power a small red indicator LED for a long time thus little reason to introduce this complexity.

What is this project? Where do you get only 0.5v? Seebek Effect thermoelectric generator? Solar cell? This project makes little sense so far.


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## kostanza

Hi 
Can you please detail more on other light element for indication that require less power and less than 1.2V
Thanks


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## ronbo

lazerlover said:


> Was wondering if any of you guys knew of a compact LED that could be powered by 0.5V, and 600mA. Many Thanks


 Silicon transistor-based Joule Thief will work down to 0.5v, but only barely. Germanium transistor usage will take that down to 0.25v pretty easily.


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## DIWdiver

TMorita said:


> The forward voltage of a red LED is around 1.7 - 1.8 volts, so of course it will not light on 1.5 volts.
> 
> If you have a ten foot wall and you have a pole vaulter that can pole vault nine foot walls, he will not be able to pole vault over the ten foot wall. It's not like he will be able to pole vault over the wall only nine-tenths of the time, or maybe only nine-tenths of him goes over the wall. No, he smacks into the wall every single time, and doesn't get across.
> 
> Toshi



Yes, but the forward voltage of an LED is not exactly a 'wall' with a specific height which you either clear or don't. At least not one that's specified in the data sheet or discussed in the community.

As you reduce the current in an LED well below the rated current, the voltage drops well below the rated voltage. It definitely doesn't head toward zero, or even closer to zero than to the rated voltage. I have seen in an array of white LEDs operating at very low current that some are emitting and others are not. It has to be pretty dark to tell the difference. This definitely suggests a 'wall' you need to clear to get light, but its height varies between supposedly identical LEDs, and is much lower than the rated voltage of the LEDs. Also, the light intensity at this operating point is normally so low that it's not even useful.

So with a ten foot (LED) wall and a nine foot vaulter, you actually ARE likely to score some points, though you aren't going to win a medal.


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## SemiMan

DIWdiver said:


> Yes, but the forward voltage of an LED is not exactly a 'wall' with a specific height which you either clear or don't. At least not one that's specified in the data sheet or discussed in the community.
> 
> As you reduce the current in an LED well below the rated current, the voltage drops well below the rated voltage. It definitely doesn't head toward zero, or even closer to zero than to the rated voltage. I have seen in an array of white LEDs operating at very low current that some are emitting and others are not. It has to be pretty dark to tell the difference. This definitely suggests a 'wall' you need to clear to get light, but its height varies between supposedly identical LEDs, and is much lower than the rated voltage of the LEDs. Also, the light intensity at this operating point is normally so low that it's not even useful.
> 
> So with a ten foot (LED) wall and a nine foot vaulter, you actually ARE likely to score some points, though you aren't going to win a medal.



This is a necrothread  ....

.. It is a wall, but it's a fuzzy wall. The "band-gap" is defined, but it's not a hard yes/no. It's a statistical process whether the electron will "jump" the gap. At lower than the band-gap, only a small portion will jump and emit light. Much higher than the band-gap, and they all do. You can add in resistive effects once you have significant current.


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## mattheww50

There is something called perpetual motion that people keep trying to achieve. The absolute minimum Vf for an LED is whatever the energy of the photon that is produced. Visible light starts right around 1 electron volt, so it stands to reason that the minimum Vf for a visible light LED is going to be on the order of 1 volt. If you could produce 1 eV photos directly from .6 V, you would have the long desired, perpetual motion machine and create energy, since each .6 eV electron coming in would produce a 1 eV photon out.


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## LEDAdd1ct

I've got a perpetual motion machine _and_ a bridge for sale, first come first serve, includes great views of the city!

Who is going to be the first to post ?


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## DIWdiver

Oops. Hadn't realized it was a necrothread. Wouldn't have posted if I had. Still, I learned something from it, so it's not a total loss!


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## Steve K

as long as this thread is running, let me ask a quick question about bandgaps, Vf, and LED color....

in the old days, as it were, the generic red LED had a Vf of 1.4V. Modern red LEDs have a Vf closer to 1.8V or more. 
What exactly changed? I assume that the chemistry has changed and gotten more efficient, but my hazy memory says that the Vf is related to the bandgap which is related to the spectrum of the photons released. 

thanks.


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## SemiMan

I am not aware of red LEDs @ 1.4 volt. That sounds more like 900 950 nanometer infrared.


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## Steve K

I looked through my parts box, looking for an old red 5mm LED. All I could dig up was a 7 segment display. With my trusty Fluke 77 (also dating back to the mid 80's), I measured 1.45V. Obviously, this is at a low current, so it's going to be greater at higher current. It's still lower than my more modern red LEDs....


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## SemiMan

Can you measure it at the typical operating current?

I assume you are just starting to light it up at 1.45V? That makes sense. It's not a hard wall for current flow. Should flatten out about 2V.


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## Steve K

at low current... 1.49V at 0.68mA






at medium current ... 1.57V at 4.78mA





at max current.... 1.63V at 19.41mA





fyi, the 7 segment display appears to be a product of HP (later known as Avago? I've lost track of all of the names), with a part number of 5082-7740, with a 023-D on the next line.
I'm betting these will never be as trendy as Nixie tubes.


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## SemiMan

-----


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## Steve K

this 7 segment display dates back to my college days... I really need to clean out my part box! 
That puts it somewhere around 1983 or so.

out of curiosity, what does "indirect band-gap" mean?


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## CkWeb

Steve, I am looking at your comparison tests and I wanted to run a LED problem by you I've been wanting to solve recently: I'm aware that red LEDs can operate well at lower values than white ones. I've been researching a hack of my swiss tools with 3mm red LEDs to see what tiny boost circuitry can be added (modded) to make them work. I have working examples of some white LEDs that run off a 1.5 volt CR1025 button cell:
http://i.imgur.com/EtffiZo.jpg

- the board on the right runs off a higher voltage LR1130 (AG10) button cell battery
- the board in the middle runs the white LED with a lower voltage CR1025 button cell battery
- the board to the right runs a red led with the same lower voltage CR1025 button cell battery

I want to mod the red LED board to do what the white LED board in the middle is doing. I don't have enough room to fit a LR1130 battery to use the LED board on the right, plus those cost a pretty penny! I've also looked at some circuits out there that look small enough to make something work:
http://www.linear.com/product/LT3466-1

There's even the LR926 (AG7) button cell battery that although has lower storage capacity it might give a white LED more power. Unfortunately I'm not electrically-competent enough to make much sense of what's actually possible to do with these little red LED boards. I wish I could just find the manufacturer of the middle boards and just get some of those, you know? I'm wide open for any help to get some white LEDs working on these little tools!

Thanks Steve.. and of course anyone else who'd like to help out or pitch-in; it's for a good cause! :twothumbs

Ps. Here are a few more images of these LED boards:
- white newer led board back : http://i.imgur.com/QKjHZlS.jpg
- white newer led board front: http://i.imgur.com/dJghSGn.jpg
- white older led board front: http://i.imgur.com/qOGvZM2.jpg
- brightness comaprison of white led boards: http://i.imgur.com/eAFzGGy.jpg


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## mattheww50

CkWeb said:


> Steve, I am looking at your comparison tests and I wanted to run a LED problem by you I've been wanting to solve recently: I'm aware that red LEDs can operate well at lower values than white ones. I've been researching a hack of my swiss tools with 3mm red LEDs to see what tiny boost circuitry can be added (modded) to make them work. I have working examples of some white LEDs that run off a 1.5 volt CR1025 button cell:




CR/BR cells are lithium primary, and are 3.0 volts, not 1.5 volts. There are no white LED's that will run off 1.5 volts. Minimum Vf for a Blue LED (which is what is underneath a 'white' LED) is on the order of 2.5 volts.


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## CkWeb

mattheww50 said:


> CR/BR cells are lithium primary, and are 3.0 volts, not 1.5 volts. There are no white LED's that will run off 1.5 volts. Minimum Vf for a Blue LED (which is what is underneath a 'white' LED) is on the order of 2.5 volts.



Still learning! 

So if they're all 3.0 volts, then these boards are using their little circuits to regulate the battery's power to the LED in some way?

Here is the older white LED board that uses the CR1025; the red LED board does not use any of these circuits:






The red LED board is on the left; it appears to feed the battery power straight to the red LED:


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## Steve K

A white LED can generate some light when supplied with less than 3V, but it is a very small amount. At 1.5V, you won't get enough to even see.

One option is to use a charge pump circuit to double the battery voltage from 1.5V to 3V. One example is the LTC1044S8. It is just a 8 pin IC and a few small capacitors. http://www.linear.com/product/LTC1044S8
My guess is that this is the sort of circuit that is shown on two of your circuit boards.


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## CkWeb

Steve K said:


> A white LED can generate some light when supplied with less than 3V, but it is a very small amount. At 1.5V, you won't get enough to even see.



The spec sheet of the batteries (LR1130) the high powered LEDs use says they're 1.55v: http://watchbatterycrossreference.com/pdfs/R389.pdf. So those boards definitely have something to boost the battery's 1.55 voltage to 3.0 because they're really bright! Here are the two side-by-side:









Steve K said:


> One option is to use a charge pump circuit to double the battery voltage from 1.5V to 3V. One example is the LTC1044S8. It is just a 8 pin IC and a few small capacitors. http://www.linear.com/product/LTC1044S8 My guess is that this is the sort of circuit that is shown on two of your circuit boards.



The space available inside these little tools is a *1cm by 1cm square space, but the height of the space is only between 1mm and 1.75mm*. The enclosures have tiny ridges inside. 

I could also try using the brighter 5mm white LED boards with a smaller 1.55v battery (SR927W). It's smaller than the CR1025: http://watchbatterycrossreference.com/pdfs/R399.pdf. If that works the LEDs would be brighter inside those tools. I'll have to squeeze the 5mm LED where the older 3mm LEDs go and getting tools w/brighter LEDs cost more!


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## rikgray

0.5 volts will be in the infra-red.

You need a dc dc voltage converter to get up to higher voltage to over come the band gap required for visible LEDs

http://ocw.mit.edu/courses/material...13/lecture-notes/MIT3_024S13_2012lec19-20.pdf


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## CuriousOne

First generation red leds were actually infrared leds, which used frequency doubling to achieve red color. Theoretically, it can be doubled even more, to get blue color and excite white phosphor. Of course, efficiency will be too low....


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## cjmessmer

The white LED in a cheap solar has 1.15 volts across it and lights up just fine.
Does anyone know where I can buy some or how to describe one so I can find them via a google search?
Thank you
John


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## ssanasisredna

cjmessmer said:


> The white LED in a cheap solar has 1.15 volts across it and lights up just fine.
> Does anyone know where I can buy some or how to describe one so I can find them via a google search?
> Thank you
> John



They do not light on 1.15V they have electronics to boost voltage.


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## brickbat

CuriousOne said:


> First generation red leds were actually infrared leds, which used frequency doubling to achieve red color....



Interesting. Got a link so we can learn more about this?


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## HarryN

brickbat said:


> Interesting. Got a link so we can learn more about this?



Here is an example of frequency doubling:

https://www.rp-photonics.com/frequency_doubling.html

The concept is widely used in laser optics, in fact nearly all of the original green and blue laser pointers used this concept.

In the NIF system, they actually use frequency tripling:

https://en.wikipedia.org/wiki/National_Ignition_Facility#LMF_and_Nova_Upgrade


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