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PLTB450B puts out only a flash

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Hello! I recently disassembled my PLTB450B laser to use it on a CNC project of my course, I already got the machine up and running, but I stuggled with the laser part.

I bought this driver to use with the laser, it claims that have TTL, needed for my project.



I did the soldering of numerous diodes in series, then inserted my multimeter as an ampmeter to read the current, I adjusted to 0,7A, the voltage with nothing on the output I set to 7,5V, then I turned everything off, discharged the output capacitor then connected the LD, when I powered up, it worked as expected, even burned a dot on the cardboard bellow it.
After 2~3 seconds it went dim, like it has LEDed. :undecided: . I checked everything again and set the current to 1,2A (was the default of my later build), same thing happened, but it only stayed bright for less than 1 second.

I removed the chinese driver and connected the old LM338 driver set to 1,2A, same thing, It cames up at full brightness and then goes dim, every time I turn it on this happens.

Tried removing the DC-DC stepdown module and connecting the driver straight to the power supply and tried with another power supply, no joy. :yabbem: .

I have a little bit of hope that the LD wasn't damaged, but contesting with my test, this is a pretty little chance.

So I ask, does this kind of thing happens? I think when a LD dies its internal cavity becomes broken, so it will never be able to lase again, but when this LD flashes, the light it puts out is laser. :confused:
 

Alaskan

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I am not sure I understand what you did, you set the output to 7.5 VDC without anything attached and also set the current to 700 milliamps? How did you do that without having a load on the output? If you simply shorted the output and set the current limit to 700 mA, that could work, using a power resistor or just shorting the output with a multimeter has worked for me in the past but is not the best way, a lot of members use laser diode test loads to set the current with that first, then insert the laser diode.

See: http://www.instructables.com/id/How-to-build-a-laser-general-guide

Example only:



I have also turned the current potentiometer all of the way down to start, and with the diode attached to the driver, slowly moved the current up with a ammeter inserted, but the leads must either be heavy low loss copper, or very short, otherwise there might be too much resistance in the leads to properly set the current. However that isn't the recommended way of adjusting as spikes could occur damaging your diode, a way better is to power off the driver, make a small adjustment, then turn it back on and see where the current is at.

Powering on and off the driver should only be done if the power supply feeding it is not turned on and off, many cheap power supplies we use put out a momentary short duration voltage spike when first turned on, or perhaps, when turned off that could happen too and spike your driver too high.
 
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Yeah, that's what I did, think of a test load, usually you have diodes and a resistor, I just removed the resistor and connected my multimeter as a ampmeter, then I set the driver to 0.7A.
Then, I disconnected everything and put the multimeter in voltmeter mode and measured the voltage across the "laser" terminals, and set the little trim pot until the voltage was 7.5V. That voltage will drop to whatever is needed to supply 0.7A.

I was looking at this site when doing this:
3dpBurner: Wiring and Tuning
 

Alaskan

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You can set the voltage to 10 VDC and it won't matter if the current limit is set to 700 mA, it will automatically keep the voltage at the needed amount to power the diode properly.
 

paul1598419

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I have lost diodes in the past like what you are describing here. It would come up to what looked like full power then get dim. Eventually, it would only come on dim. That was how I lost my first S06J 405nm diode. We, and by we I mean you, are still overdriving this diode at 700 mA. Now, I can't say that the Chinese driver didn't have a hand in it happening now, because it could have.
 
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pltb450b can handle up to 1.8A current so overdriving isn't the case here.

I have lost diodes in the past like what you are describing here. It would come up to what looked like full power then get dim. Eventually, it would only come on dim. That was how I lost my first S06J 405nm diode. We, and by we I mean you, are still overdriving this diode at 700 mA. Now, I can't say that the Chinese driver didn't have a hand in it happening now, because it could have.



do you have a good heatsinking on your diode?it could happened if you powered a bare diode or only with the housing.
 
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You can set the voltage to 10 VDC and it won't matter if the current limit is set to 700 mA, it will automatically keep the voltage at the needed amount to power the diode properly.
Agreeded! :beer:

I have lost diodes in the past like what you are describing here. It would come up to what looked like full power then get dim. Eventually, it would only come on dim. That was how I lost my first S06J 405nm diode. We, and by we I mean you, are still overdriving this diode at 700 mA. Now, I can't say that the Chinese driver didn't have a hand in it happening now, because it could have.
That is hard to know, because on my test load it worked at expected, this is sad because lets a little hope that it will work again.

pltb450b can handle up to 1.8A current so overdriving isn't the case here.
On the past I was supplying it with 1,2A, to get maximun longevity, as I didn't knew this driver, I started with 700mA.

Now a thing that came up and may be the culprit, does transporting a laser diode cause damage? I was transporting my CNC from my house to my course and vice-versa through my car with the laser module attached to the head.

For now I'll keep going with the trusty LPC-815 @ 400mA, because I have no time left to wait the shipment of a new blue LD.

Thanks all for the replies. :beer:
 
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Cyparagon

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I set the driver to 0.7A.
Then, I disconnected everything and put the multimeter in voltmeter mode and measured the voltage across the "laser" terminals, and set the little trim pot until the voltage was 7.5V
I don't understand. You set the trimpot to one setting, then you set the trimpot to another setting? Are there two trimpots? What is the current input and output at 7.5V?
 

paul1598419

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There are two pots on this driver. I suspect the multi-turn pot is for current, the other is a cheap open pot on the other side of the board. I don't get the need for a voltage setting either, but this is not the first time I've run into one.
 
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I don't understand. You set the trimpot to one setting, then you set the trimpot to another setting? Are there two trimpots? What is the current input and output at 7.5V?
There are two pots on this driver. I suspect the multi-turn pot is for current, the other is a cheap open pot on the other side of the board. I don't get the need for a voltage setting either, but this is not the first time I've run into one.
Yep, two trimpots, the blue for current and the tiny for voltage, I think the idea was to be able to use it as a buck regulator with current limit.

I assembled another diode, a LPC-815 and set the current to 0,4A, it powered up as usual, very bright red light, then I disabled the driver using the TTL function, the light went down as expected. Then, I enabled it with TTL and .. the laser diode died, it lighted up as a LED.

So the culprit was the driver, this chinese driver screwed up my project, Now I'll try to find a 405nm one that suits my needs.
 

paul1598419

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Yeah, failure is how we learn things around here. Better an LPC-815 than a much more expensive diode. At least now you know. There are many drivers made for engraving. There are plenty of good ones out there. Good luck. :yh:
 

Cyparagon

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Oh, the picture didn't load the first time I viewed this.

I'd venture a guess this is more designed for battery charging. NiZn, all types of lithium, and all lead-acid are best charged with constant voltage with a current limit. The problem is rechargeable cells don't give two shits about noise or spikes, so the manufacturers often omit any attempt to mitigate this. The couple that I have tested have horrendous stats in these areas. Don't power a laser with an unknown driver like this until you can characterize it with an oscilloscope.
 

paul1598419

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That would certainly make sense since it has a voltage set pot. The Chinese are infamous for repurposing circuits for uses other than what they were designed for. I'm sure it was sold as a laser driver, but it likely just isn't.
 
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Thanks for the answers! :thanks:

Yeah, that makes a lot of sense, for a laser driver it has no point to have a voltage set pot at all.

It is being sold as a laser driver, here is the link if anyone is going to buy it.
https://www.aliexpress.com/item/2W-...32819928099.html?spm=a2g0s.9042311.0.0.Kpdj5N

I'm going to buy a 405nm 1,6W laser with the driver included and 6 months warranty, not spending money with those things anymore.

:thanks:
 

paul1598419

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Aha. You can see in the third photo down the "upgraded board" has now got "Laser" on the back side while the original just says "power". I think that photo is the smoking gun as there is no difference between the two boards except for those words. I hate Aliexpress. I never buy laser related items from them. They have no idea what they are doing.
 
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Good news! My board comes with the "laser" label on the back! (ehr, no!)

So this board will get another uses, far far away from my lasers of course. :p
 




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