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How best to "Simulate" a Laser Diode

LarryQ

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Lets keep this simple and as an example use the GB 16X diodes.

As people roll their own circuits, the ability to fine tune their results will require a good safe way to simulate the properties of the Laser Diode, using something more robust, and cheap.

Something that we can place in the circuit...meter out voltage, and current, and "Proof" our work BEFORE we wire in our hard to come by Laser Diodes!

Obviously, a regular LED comes to mind....but what one (or more) will best simulate out Laser Diodes???

When we think about the New and more expensive Blu-Ray diodes...the ability to "Proof" out circuitry becomes even more important!!!!

Thanks

Larry
 



Daedal

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I answered it in the other thread... I guess I'll just copy it to make sure it's saved here then :)

--DDL
 

Daedal

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Larry, to (as close as possible) simulate a laser diode, use 4 X 1N4001 rectifier diodes in series instead of the LD. At .7V drop each, you have a 2.8V drop across them, which is the most common voltage drop I see on LD's like this. A laser diodes, or any diode for this matter, is a current drain. It simply drops the voltage going through it by some amount and then passes all the current across. If it manages to get too much current (which is loves) it gets too hot and then dies! With the diodes wired in series you get a perfect idea of what a LD will do when hooked up... except the whole coherent light thing ;)

If you want to go one step further, you can use regular LED's. They are the same thing, but they will have a higher V-drop. I would use 3 or 4 of them to make a nice big V-drop and then test to make sure that the voltage, across the whole bunch, is what it needs to be. If the voltage across all that many diodes is too high, then your supply voltage is too high, if it's low, then it'll simply be low. Using a single LED with, say, 2.6V drop would only simulate the circuit up to 2.6V. If you then add another one in series you should notice that he voltage drop is a maximum of 5.2V, but if you get more than 3.5-4V then you should try cutting it down. The current will always be the same regardless of what diode you use, it's the voltage + current that make the difference. They have to be just right :)

Current still gets the higher precedence of the two though :p

--DDL
 

naplam

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Yellow and green leds have about 2.5V drop, so they're the most similar. But they'll burn unless the current is quite low (they usually glow red first, that's a first warning you're going to break it), so you'd have to use several in parallel to test high currents.
 

Benm

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I use a 1W red led (like a luxeon star) to test current sources and such. Electrical characteristics are similar to that of a laser diode (voltage drop is a bit lower), and it gives nice optical feedback. These leds can handle up to 350 mA by design, so no worries there.
 

LarryQ

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I thought this info should be out here on it's own.
THis will be very valuable info to those who are wiring their GB LD's for the first time!!!

Thanks for understanding!!!

Larry
 

Kenom

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Benm said:
I use a 1W red led (like a luxeon star) to test current sources and such. Electrical characteristics are similar to that of a laser diode (voltage drop is a bit lower), and it gives nice optical feedback. These leds can handle up to 350 mA by design, so no worries there.
Most luxeon LED's I've seen can take up to 1500ma before they start reaching dangerous levels for the diode. 350ma is like it's minimum. For example the luxeon 1 was designed to run at 750ma. These do make perfect LD dummies in new circuits.
 

LarryQ

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I tried a Luxeon star (that is the stock LED that comes in most LED flashlights)....

Using that I saw 3.1 volts and only 140 Ma....

I am going to require more than 140 Ma in my current project.

Using a LM317 in TO-220 size, 6 volts input (2 cr123 e2 lithiums) and a single 1/2 watt 5.1 Ohm resistor across the LM317 for feedback to the Adj leg.

Larry
 

Benm

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Make sure to get a RED power led.. the white ones run at higher voltages for a given current, usually in the order of 3.5 volts or so.

Most luxeon LED's I've seen can take up to 1500ma before they start reaching dangerous levels for the diode. 350ma is like it's minimum. For example the luxeon 1 was designed to run at 750ma. These do make perfect LD dummies in new circuits.
Depends on the luxeon really. The luxeon-1 was designed for 1 watt of electrical power, that's around 350 mA at 3 volts. They will survive a lot more when cooled properly though.

Most white star-mounted leds offered now are built for more power, 3 to 5 watts usually. You can use all of them as dummy lasers, but the require a bit higher voltages than LD's do. No problem for a constant-current source.
 

a_pyro_is

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I also use 4 x 1N400x as a dummy load. But my favorite dummy load is a high power LED like a luxeon in series with one Si diode so that the V drop is just a bit higher than a red LD.
 

Daedal

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naplam said:
Yellow and green leds have about 2.5V drop, so they're the most similar. But they'll burn unless the current is quite low (they usually glow red first, that's a first warning you're going to break it), so you'd have to use several in parallel to test high currents.
If you put 10 LED in series... they are all sharing the voltage, but they all get the same current ;) I think you meant parallel? But that defeats the purpose of making the voltage drop higher.

I like using the ones I salvage out of DX flashlights. Using a couple in series really is one of the best solutions. Although, specifically chasing after them could be quite expensive :-? Cheaper than an LD though ;D

--DDL
 

naplam

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yeah, i said parallel, read it again lol ;)

There's something i really recommend for simulating circuits. Much easier than solving equations:
www.ni.com/multisim
 

Daedal

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Yeppe... you got me... ;D I read it and didn't look again...

Sorry :-[

Well... I did use Multisim before, I probably have the CD somewhere around here..

--DDL
 




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