lazerlover
Newly Enlightened
- Joined
- Jul 6, 2007
- Messages
- 35
Was wondering if any of you guys knew of a compact LED that could be powered by 0.5V, and 600mA.
Many Thanks
Many Thanks
ultra low voltage LED?
- Thread starter lazerlover
- Start date
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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.
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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.
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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 
TigerhawkT3
Flashlight Enthusiast
You could try adding a Joule Thief (works down to a third of a volt, apparently).
Jarl
Flashlight Enthusiast
yeah, but the efficiency is horrible for that
DM51
Flashaholic
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.
Black Rose
Flashlight Enthusiast
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.
All of the posts in the other thread are from folks that didn't post in this thread.
Black Rose
Flashlight Enthusiast
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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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.
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.
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.
DIWdiver
Flashlight Enthusiast
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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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.
mattheww50
Flashlight Enthusiast
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.
LEDAdd1ct
Flashlight Enthusiast
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
?
Who is going to be the first to post
?
DIWdiver
Flashlight Enthusiast
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!
Steve K
Flashlight Enthusiast
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.
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.
