Willie TwoFinger

I have a project that I’m working on and need a bit of direction here. I need to power 155 laser diodes rated at 650nm 5mA, 3.2 v. The diodes run at around 30mA each.

I bought this power supply

http://www.trcelectronics.com/Meanwell/pdf/rs35.pdf

Do I just use a triple pronged extension cord, cut off the end, then:

- place the live wire into pin 1 (L, AC) - neutral into pin 2 (N, AC) - ground into pin 3

I have a 6ft extension cord: 13A - 125V - 1625W

Or am I way off here? Any problems I need to be aware of?

Thanks for any help...

Gayan Soyza

Your connection is ok.If anything happens even no problem you get warranty to that power unit.

I'm wondering about that number of Laser diodes.The drawing current depends on how you connect the Laser diodes.

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Gayan
Forum Supporter

Willie TwoFinger

Thanks Gayan,

Those diodes are going to be connected parallel (all positives together/all negatives together?). Here is the thread that explaines how the diode was tested;

http://regrowth.com/hairloss-forums/...fm?f=1&t=20527

Note: a diode was tested at 27mA with a 5.2v adapter. 30mA is just an approximate...

rjvh

what is the voltage of the supply you bought ??

no matter which one you bought they're all sufficient to supply what you need but personaly i would taken a higher voltage and put the LEDs in serie rather than parrallel
if you would have taken 24V you could make 22 strings of 7 LEDs which would consume +/- 0.66 amp totaly

if you conect all LEDs parrallel it needs 4.65 Amp at 3.2 Volt


Robert-Jan

Torben

I agree with Robert-Jan that you would do better to put the diodes in series-parallel (i.e. have several strings of diodes, each string current-limited) instead of just putting them all in parallel, and I have the same question: which of the 6 power supplies listed in that PDF did you buy?

Do the laser diodes include their own current-limiting resistors?


Torben

audioguru

The tests used the resistance of the current meter plus the resistance of its probes to limit the current. Without the meter then pure luck might limit the current.

I wonder how many of the 155 laser diodes will survive without current-limiting resistors? Half of them?

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Uncle $crooge

Willie TwoFinger

rjvh, Torben ...

I bought the 3.3V model.

The diodes, hmmm, not sure about the current-limiting resistors... Here is a better idea of what I have;



Well, they each have a little circuit board on it. Might that indicate current limiting?

audioguru... I definitely do not want to burn out any diodes.

audioguru

Your laser diode circuit must have a manufacturer's name. The manufacturer must have a detailed datasheet for how to use it.

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Uncle $crooge

Willie TwoFinger

audioguru...

Thanks, I just emailed them to find out for sure. I do know of a few people who are using these same diodes (some for around five months now) with no problems. They are using way less than what my gadget has though.

My biggest concern is hooking them up properly, with one good PS, and as safely as possible!

Willie TwoFinger

rjvh, or Torben ...

What are the advantages of putting them in series?

As you can tell, I know little on how this all works!

Thanks!

audioguru

If you tell us the name of the manufacturer and the part number of the laser diode assembly then we can look it up immediately without waiting for e-mails.

www.datasheetarchive.com and Google have never heard of the HLM-8013B.

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Uncle $crooge

Willie TwoFinger

Manufacturer: AixiZ Service & International, LLC

part number: A-H650-5.0-3

ikalogic

I have a very similar lazer diode, and it DOES have a current limiting resistor, i even tried to boost it by providing 12V and it didn't complain a lot!

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Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/

Torben

From the image you posted it looks like it would contain its own current source circuit, but it's impossible to tell for sure. The specs you posted don't list typical diode-type specs (such as forward voltage etc). I suspect this means that it does in fact include a current-limiting resistor BUT I don't know for sure. If you blow them out using this post as a recommendation, it's on your own head.

As for the series/parallel thing: diodes are not perfect devices. If they were perfect then there would be no problem wiring them in parallel but in reality they vary slightly from one diode to the next, even of the same type/colour/rating/etc. So when you put them in parallel they do not get a perfect distribution of the current; some of the devices draw more and the others less. You can get runaway effects where one draws all the current and dies. Then the next one pulls the current and dies, and so on.

You can get around this problem in a few different ways. One would be to leave the LEDs in parallel but put a current-limiting resistor in series with each LED. You can probably quickly see why this is ridiculous for large numbers of LEDs: you have one resistor for each LED. Also, the current drawn is high (Iled * the number of LEDs).

Another solution is to put all the LEDs in series and just use 1 resistor to limit current. Since in a series circuit the current is the same at all points in the circuit, the current over the individual LEDs can't get unbalanced when they're wired in series. The problem with this solution is that while the current drawn stays low, you need a voltage of (Vled * the number of LEDs) volts to drive the series. For 155 3V LEDs that would mean you'd need 465V-plus power supply.

So a common solution is to compromise by arranging the LEDs in several equal strings, with each string having its own resistor, and putting the strings in parallel. Then the voltage needed is (Vled * number of LEDs per string) and the current drawn is (Iled * number of strings)--you can vary the number of LEDs per string and the number of strings to match your power supply.

Hope that made some kind of sense. Disclaimer: I'm no electrical engineer. I'm just some guy with a soldering iron and this is a hobby.

Erm. One more thing. You have a 3.3V power supply and 155 lasers which require at least 3V each, and which draw 50mA (from the spec sheet you posted--I know this disagrees with your first post but design for the worst case scenario). You should be fine putting them all in parallel except your power supply will be over spec (155 * 50mA = 7.75A; the power supply is rated at 7A). You could try running them in groups of 2 to bring the current draw down to around 4A but then you're trying to run 6V per string on a 3.3V supply.

I hate to say it, but unless I'm missing something, I don't think your power supply is up to the task of running all 155 laser modules--at least, not while staying within its rates specs. I hope I'm wrong. If I'm right, I hope you kept the receipt.


Good luck,

Torben

Hero999

It might even have a built-in constant current source meaning that the brightness would stay the same, even if you increased the voltage.

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