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12-05-2016, 07:28 PM #1
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Running Multiple Lser Diodes. (NUBM08)

Hello everyone, I welcome myself to this great forum and hope you guys can help me with my current situation

I’m going to categorize this into A) B) C)

Recently just bought a 08 Laser Array and need to know how to get this boy working! I will run you through my maths and hopefully you will see where I am at with this project; So lets jump right into it.

A)

So for this Spec (working operation in Series)
Operating Voltage = Mid 34V & Max 38V
Operating Current = 3.5A

So how exactly do I get this working!? If you haven’t already watched; Styropyro has done this, Titled 40W Laser Shotgun on YouTube. So clearly it is possible. From the amount of cable I saw I believe he wired his in parallel.

*So as we know in Series, Voltage splits and Current stays the same
so from our Values above the wiring configuration would equal:

Series = 34V / 8 = 4.25V Mid
Series = 38V / 8 = 4.75V Max
Series = 3.5A in each LD

So now we know this, what do I do next!?

B) Series.

So with LD I am quite familiar that these boys love to suck current, so we need to limit this so they down melt on me.

Using an LM317 current Regulator Formula
Resistor Required (Ohms) = 1.25V / Nominal LD Current (3.5A) = 0.357 Ohms.(I got this formula from the internet, so please tell me if it is correct or not)

However I read that LM317’s lose there Efficiency after 0.2A or 200mA and I know they don’t work over 1.5A, therefore 3.5A / 0.2A = 17.5 LM317. so 18 LM317 are needed to make this run as efficiently as possible. I also know LM317's are okay up to 38V so we're good there.

So now that we know this I will need 18 LM317's and run this in parallel so that the current is split. So now LM317 current limiter equation 1.25V / 0.2 = 6.25 Ohms wired to the LM317. (Adjust to Vout)

So 18 LM317's ran in parallel with 6.25 Ohms wired across Adjust to Vout. is all correct so far?

C)

So now that’s all done and I hope you understand and follow with me. How do I select the Power supply!?

What if the Volts are too high, will I need to make an adjustable Voltage regulator? and if I do, will this need to be in parallel because the amps are not efficient after 200mA if you remember

And if the current is too high say 100A and I need 3.5A will I need to use a higher resistor?

If you guys can help me out here I will be very grateful, thank you.

Thanks,

Bowler

Last edited by Bowler; 12-08-2016 at 11:59 AM. Reason: Typo error

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12-05-2016, 07:46 PM #2
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Re: Running Multiple Lser Diodes. (NUBM08)

Styro I believe used 3 x LM317's for each diode, 8 sets of 3 and the 3 being in parallel I do believe.

PLEASE do not spell out the name of the diode bank manufacturer, spell it as N1ch1x, we will know what it is because it causes the search engines to pull our threads and it's a problem, Thanks.
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12-05-2016, 07:47 PM #3
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Re: Running Multiple Lser Diodes. (NUBM08)

Have you built any lasers before? Any experience with lasers at all?
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12-05-2016, 08:10 PM #4
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Re: Running Multiple Lser Diodes. (NUBM08)

Quote:
 Originally Posted by RedCowboy Styro I believe used 3 x LM317's for each diode, 8 sets of 3 and the 3 being in parallel I do believe. PLEASE do not spell out the name of the diode bank manufacturer, spell it as N1ch1x, we will know what it is because it causes the search engines to pull our threads and it's a problem, Thanks.

So THAT'S why we don't spell out the name

I've been wondering for quite a while now!
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12-06-2016, 09:13 AM #5
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Re: Running Multiple Lser Diodes. (NUBM08)

Hi all,
Yes I've had a few lasers made before, just something like the one is a bit different. If you could answer my questions within the thread that would be good. And if you do, can you explain why please. Going to be making this project this weekend. I've done all the maths now and understand what to do. Just my confidence is probably an issue. But laser mostly revolve around ohms law, a few driver formulas and then just making the maths fit.

So please let me know what you think

12-06-2016, 09:15 AM #6
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Re: Running Multiple Lser Diodes. (NUBM08)

Hi red.
Did he wire to the LD's in series or parallel?
From the maths in my thread I know that they will be parallel. It just depends on how many lm317s you have due to the power supply output

12-06-2016, 02:57 PM #7
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Re: Running Multiple Lser Diodes. (NUBM08)

If you are using 7.4v cells you could use a LM 338 for each laser diode, or a LM 1084 is a low dropout that will handle 5 amps, but I would stay 4.5a or less with the NUBM08's, there will be a lot of waste heat.
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Last edited by RedCowboy; 12-08-2016 at 11:54 AM.

12-06-2016, 03:14 PM #8
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Re: Running Multiple Lser Diodes. (NUBM08)

Just remember if you run the LM regulator in CC mode with a resistor you need to add 1.25V to the total dropput voltage .
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Last edited by DashApple; 12-06-2016 at 03:20 PM.

12-06-2016, 05:58 PM #9
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Re: Running Multiple Lser Diodes. (NUBM08)

Hi red, I'm from England, so sorry if the meanings are different. What do you mean by 7.4V cells? Is that a 7.4V battery? if so, could you explain why I need a 7.4V battery when the LD works below.
Series = 34V / 8 = 4.25V Mid

And thanks for the different LM's I will look into them and see which one would be best suited.

12-06-2016, 06:01 PM #10
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Re: Running Multiple Lser Diodes. (NUBM08)

Hi DashApple,

I'm aware of the drop out voltage. But what do you mean in CC mode ? If I had 4 LM317's would this be 1.25V x 4 to cover all 4 dropout voltage.

12-06-2016, 06:09 PM #11
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Re: Running Multiple Lser Diodes. (NUBM08)

Quote:
 Originally Posted by Bowler Hi red, I'm from England, so sorry if the meanings are different. What do you mean by 7.4V cells? Is that a 7.4V battery? if so, could you explain why I need a 7.4V battery when the LD works below. Series = 34V / 8 = 4.25V Mid And thanks for the different LM's I will look into them and see which one would be best suited.
Need 7.4V when taking into account the dropout voltage, which is 2.5V in CC I believe due to the series resistor?

Quote:
 Originally Posted by Bowler Hi DashApple, I'm aware of the drop out voltage. But what do you mean in CC mode ? If I had 4 LM317's would this be 1.25V x 4 to cover all 4 dropout voltage.

CC mode = Constant Currant mode. Laser Diodes need a current regulated supply, not voltage regulated.

No, it'd be 1.25V total, you'd be connected the LM317s to the power supply in parallel.
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Last edited by diachi; 12-06-2016 at 06:11 PM.

12-06-2016, 06:56 PM #12
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Re: Running Multiple Lser Diodes. (NUBM08)

Hi Diachi

So why do I need the 7.4V when you mention its 2.5V. Can you explain this please and with the maths if possible.

And cheers. Iknow they will be connected in parallel, as this is better for the amps

12-06-2016, 07:13 PM #13
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Re: Running Multiple Lser Diodes. (NUBM08)

Running the diodes in parallel may present you with many difficulties. Having the diodes in parallel depends on all the diodes having exactly the same forward voltage drop. This is unlikely and will result in some diodes being overdriven and some barely turning on. Connecting them in series ensures that the same current will be passing through every diode in the array.
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12-06-2016, 07:22 PM #14
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Re: Running Multiple Lser Diodes. (NUBM08)

12-06-2016, 07:36 PM #15
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Re: Running Multiple Lser Diodes. (NUBM08)

Sorry for any misunderstanding but, from your eaarlier post..." Iknow they will be connected in parallel, as this is better for the amps".

From your original post: So now that we know this I will need 18 LM317's and run this in parallel.

Hooking them up in series will be very advantageous as you'll only need one regulator.
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Last edited by WizardG; 12-06-2016 at 07:40 PM. Reason: added content

12-06-2016, 07:37 PM #16
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Re: Running Multiple Lser Diodes. (NUBM08)

Quote:
 Originally Posted by Bowler Hi Diachi So why do I need the 7.4V when you mention its 2.5V. Can you explain this please and with the maths if possible. And cheers. Iknow they will be connected in parallel, as this is better for the amps
The LM317 needs an input voltage at least 1.25V above the output voltage. In your case the output voltage will be ~4.25V for the drop across the diode and another 1.25V for the drop across the series resistor.

So you've got 1.25V+4.25V = 5.5V out. You need an input voltage that's at least 1.25V above that, so 6.75V. Some wiggle room is nice to have.

Those LDs can run higher than 4.25V too I believe, maybe up to 4.5V if you drive them hard enough, although I could be wrong.

Quote:
 Originally Posted by WizardG Running the diodes in parallel may present you with many difficulties. Having the diodes in parallel depends on all the diodes having exactly the same forward voltage drop. This is unlikely and will result in some diodes being overdriven and some barely turning on. Connecting them in series ensures that the same current will be passing through every diode in the array.
You need balance resistors when running in parallel. For the sort of currents used with these diodes you'll need some fairly beefy balance resistors too.

Series is probably the easier way to do it. That or have individual drivers for each diode, perhaps with regulators in parallel ... which still requires balance resistors IIRC.
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Last edited by diachi; 12-06-2016 at 07:38 PM.

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