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Heat control of diode vs driver?

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ajhalls

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I am building a laser maze and have ordered a variety of lasers from 5mW to 20mW on ebay. I want to standardize them but am trying to find the most economical one that keeps a good quality beam after a few mirror bounces.

I have ordered a few where the driver is a circuit that hangs out the back quite a bit, like this one:

INDUSTRIAL/LAB 532nm 10mW 5VDC Green Laser DOT Diode Module | eBay

That one worked great till it got hot while I was setting it up ~10 minutes continuous use. Now it is pretty dim, and gets dimmer over time. I am not sure if I damaged the diode, or the driver.

I have a metal lathe and can make some heat sink housings for the laser, but it seemed like most of the heat was from the driver, so maybe I should focus on that instead, but I am not sure why they would have put heat shrink tubing over the driver if it needed so much heat dissipation.

I am using a raspberry pi with a 16 relay setup to turn the lasers on and off and considered using a single driver before the relay and just getting a bunch of bare diodes without drivers and building my own housings with heat sinks, but if the major heat is generated by the driver, then I wouldn't have to worry about cooling the diode as much as cooling the one driver back at the control center.

I do realize that if I setup 8 lasers in parallel and start turning them off one by one it would raise the power sent to the rest, so maybe I could adjust the driver output using the raspberry pi using something like this: 0- 2100mA Adjustable Constant Current Laser Diode Driver 12V input | eBay and control it with the raspberry pi.

So I guess the big questions I have are:
  1. in the 5-20mW range, which needs cooling most, diode or driver?
  2. Which is most likely to fail first?
  3. Ok to group the lasers on one driver?
  4. Which is most likely to fail first?


I also picked up this 50 pack: 50PCS 650nm 5mW Laser Red Dot Module red laser sight laser diode laser pointer | eBay

I found the failure rate to be acceptable where about 20% of them have horrible focus, and they seem to be able to be left on for hours without any problems, but they aren't as bright as I would like, and I would love to switch to green from a visibility standpoint, but from a cost perspective, until I get all this worked out and find how to reduce my failures I will stick to the reds :)
 





1) Diode
2) Depends on the manufacturer, and how hard the device is driven. Both will last for well over 10,000 hours ideally.
3) No. Not without complex additional circuitry.

You can adjust the focus on those cheap red modules. The lens assembly is secured with glue, but it is very weak glue. Twist the front to adjust the focus.

For low power like you're using, a resistive dropper is the best way to drive these. It is simple, will never fail, and is ultra cheap.

DPSS greens (532nm) are cheaper, but often far less reliable than direct injection (515/520nm) greens. They're also far less efficient.

As with most things in life, you have to choose between good quality and low price. You cannot have both.
 
Thank you so much guys, I had no idea that I could adjust the focus on those cheap red ones, looking at it I thought it was just a solid piece of brass.

I have done some work on my setup and the wall mounts should now be able to support the weight of a setup like RedCowboy's link, before they were just neodymium magnets holding on to the screws in the wall :)

When buying drivers / collimating lenses, I see the guys on ebay specifying the nm range it is supposed to be for. My first reaction is that they are doing that for marketing purposes to make sure it shows up in search results, but that there isn't any difference in driving a green vs red laser, or focusing it for that matter. Am I wrong?
405-G-2 Glass Collimating Lens w/Holder for 405nm 445nm 515nm Laser Diodes | eBay
Adjustable 515nm 520nm 530nm green Laser Diode Driver Power for 30 ~ 120mW laser | eBay
 
ajhalls said:
Thank you so much guys, I had no idea that I could adjust the focus on those cheap red ones, looking at it I thought it was just a solid piece of brass.

I have done some work on my setup and the wall mounts should now be able to support the weight of a setup like RedCowboy's link, before they were just neodymium magnets holding on to the screws in the wall :)

When buying drivers / collimating lenses, I see the guys on ebay specifying the nm range it is supposed to be for. My first reaction is that they are doing that for marketing purposes to make sure it shows up in search results, but that there isn't any difference in driving a green vs red laser, or focusing it for that matter. Am I wrong?
405-G-2 Glass Collimating Lens w/Holder for 405nm 445nm 515nm Laser Diodes | eBay
Adjustable 515nm 520nm 530nm green Laser Diode Driver Power for 30 ~ 120mW laser | eBay
Click to expand...


There often is a difference when wavelength is specified. For example, when a lens specifies a specific wavelength it usually means that it has AR (anti-reflection) coatings for that wavelength. Those coatings will only work well near that wavelength and may reduce efficiency at other wavelengths. Focusing and such will still work mostly the same, other than the somewhat shorter focal length you'll see with shorter wavelengths and losses incurred by any incorrect AR coatings.

As for drivers, different wavelength LDs have different input voltages (different semiconductors/compositions required for different wavelengths, much like LEDs), so your choice of driver is important there too. The driver you linked to for example would be no use for a 532nm DPSS laser as the diode's forward voltage is ~1.8V for those, not the ~7.5V from this dirver. It is however fine for a ~515nm diode, as the forward voltage for those is ~7.5V. Keep in mind laser diode drivers are constant current, so the driver will try to adjust the voltage output to maintain the correct (set) current for the load, but if the required voltage is too far outside of the drivers range then it'll either damage the load, or the driver or just not work.

So diode, driver type (i.e. buck/boost, available output/current range) and power supply choice all matter when picking a driver.
 
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Thank you for answering what must seem like some simple questions, you have saved me from making a lot of mistakes :)
 
As for the temperature sensitivity: DPSS lasers (532 nm green, 473 nm blue) are often very sensitive to operating temperature, and can dim when they get warm. Often this does not actually damage the system, and it will work at full brightness again once cooled down completely. Others need to warm up a bit before achieving full output, and this can even vary between the same lasers coming from the same supplier.

Direct lasers like the red ones, and 510/515/520 nm green ones, are less sensitive to temperature. Overheating them can certainly do damage, often irreversible, but they don't really do that thing dpss lasers do where they go dimmer and brighter with temperature without lasting effect/damage.

As far as those 10 mW red units go: if they last the first hour they'll probably last forever, there is little strain on anything in these unless they used the cheapest of crappy diodes and 10 mW is still overdriving them. At such low power level the driver should last foreve really, it just doesnt get warm.
 
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