How to determine voltage needed.

I have seen lots of laser projects with 2.5 volts used and even 9 volts...

For instance my 120mW green uses 2 AAA or about 3+ volts.

But what dictates this?

I had some red diodes from a nice lightscribe burner, threw 2.8 volts into them and bam, dead in 2 seconds, were pretty bright though while it lasted.

I know current killed it, but how do you know what voltage to use on any given diode?

I am assuming there are several types of diodes that require different voltages? but then again, how would you know by just looking at one?


Thanks all........

Well, you read about everything, then you'll know these things. Wait for photonaholic to post and you should have a ton of information to read about.

Also, read as much ad you can about drivers and "green diodes".

Solar --

Some posts here don't provide much help. Using the search feature is almost a required start here .... BUT...

Each diode type, chemistry, color etc has a diode junction opperating voltage range. 808, 635, 650 ...... 405 nM are all different and usually increase as the wavelength decreases. The required supply voltage is determined by the diode and the driver configuration.
Read and learn.

HMike

Zaery -- If you read about everything, you will be able to provide extra help. Sometimes, info like above triggers someone to look for more specific data.

I was under the assumption that the typical red diode needs 3 volts, which is what many simple pointers require...

I have torn so many laser diodes out of low and high end equipment, and by high end, I mean laser copiers and other photo devices, but I thought they all were 3 volt requirements...

Few were dead to begin with, but I killed a few on my own...

I also tested for IR since that could have been an IR diode for burning images, and I used a method I designed myself that works pretty well for testing green lasers as well for IR filters..
I shared this once on the WL site, but I have been banned for 2 years now for no appearant reason...

Solar ---
You really need to use search. Red diodes from disk players, printers etc are not burners. Yes ~ 3 volts will be about right for red but IR diodes will be more around 2.7 volts and high powered reds about 3.2 volts. These voltages will vary somewhat but in your reading here, you will see that the voltage spec is only a range. That's why you will see repeated many times that we use a current source as a driver. Don't use a battery direct.
Please read the stickied info here.

HMike

ok, The voltage requirements of the diodes vary as has been stated before. But also you need to account for how much voltage the driver requires as well. there are boost drivers, and linear drivers. you can buy a rkcstr driver which is linear, or a flexdrive boost driver fairly easily, or make a driver yourself. Take a boost driver, hook it up to a LOC 16x red diode, and a linear driver and hook it up to a LOC 16x driver. set both diodes to 400mA. you end up with two diodes, at the SAME current level, but the flexdrive will run nice and happy off of 3 volts, where as the rkcstr driver will need around 5 volts. The flexdrive would power a blu-ray laser as well with only 3 volts. however the rkcstr driver would need 7.2 or more volts. again, same diodes same power, different voltage required by the different drivers. As a side note, you could feed the rkcstr driver 12 volts instead of 7.2 and it would be just fine. and 3 volts simply wouldn't be enough to make the diode start to lase.

Also, if you read through a couple diode testing threads such as this one
http://laserpointerforums.com/f50/flat-red-laser-diode-testing-2nd-phase-47044.html

you will see that a red diode needed 1.72 volts at 26mA, however the current was increased to 516ma and the voltage required went up to 3.14 volts. This is in the same diode. A LOC diode at the same power level needed 3.45 volts. so two different RED diodes, same current and two different required voltages...... You might get the idea it's not just a simple answer as the voltage required seems to vary considerably....

Also keep in mind a battery doesn't give an exact voltage either. I power my LOC with 2 3.7v lithium cells. (aaa sized) however fully charged they are putting out 4.2 volts. the voltage will considerably below 3.7 volts before they run out as well. (2.something)

Remember, the current in mA is more important then the voltage going to the diode. I doubt you will be running 20 or more volts through a diode anytime soon just powering it with regular batteries. So basically too few volts will not be enough to turn it on, and shouldn't hurt anything. where as you need more then a couple extra volts to hurt it. But the current in mA of course is a different story entirely. What killed your diode was way too much current. To decide how much voltage to power one, first select and purchase a driver, then look at how much voltage the driver will need...

As far as killing your red diode, what did you power it with? you did use a driver right? and what did you set the current to?

this thread has a lot of useful data. you can see a lot of info on specific diodes. Just keep in mind things like how much voltage is required DOES vary. and you don't need exact voltages.

http://laserpointerforums.com/f51/diodes-compilation-all-diodes-data-one-thread-45042.html

Thank you..

The only reason I asked this question was because,

1. the drivers you listed above were the very thing I read since I am building my own driver for a project, and i saw the different voltages in them and was a little confused..

2. been out of the laser tinkering hobby for a few years.


On a side note, the diodes I had were a mix of IR, Burning, and reading...
Hemlock, no disrepect, but you sound bothered by my question.

The laser copier I got one out of was an IR laser, quite capable of burning but I knew not much about it at the time, and killed it with a DC power supply of 6volts.
It came in it's own focusing housing with a focus range of less than 1 mm...in and out of focus..
This I found out by using a red diode in it, unless the IR and Red spectrums focus differently in comparison.




I do search forums, and read reviews, reports, results,,,,,,,,LOTS...
I'm an astrophotographer
Amateur scientist.
and inventor...
Not a dummy.

My question really was how can you tell what the requirements of a diode are beyond, just building a circuit...and throwing voltage at it..
For diodes that aren't labled or known..
BUt I guess it doesn't matter too much..


Stridast, you answered it easily thanks...

Yes it does matter. First, you don't apply voltage to a diode. We apply current. That is how we test diodes. The voltage will fall into a range depending on the diode. You will see that we plot Po vs mA in most of our graphs. We are looking for threshold, slope and "kinks" or a knee in the graph to indicate that the limit is being reached and then we back off or push it to distruction.
That's how we run a basic test on an new or unknown diode.

HMike

Thanks Mike.
That sums up a lot.

I will choose my words more carefully when it
comes to voltage or current.

Usually my diode tests just used a few
LED's in parallel as a dummy load to drop current.
Since I had 800mA I figured a few would do it
Now I want to do it right.