ready to pull my hair out

[gary s]

i have been working on this project for a month. but i keep burning out my diodes.
my project is a photo switch using a 5mw laser as the light source. the photoswitch circuit works great and the laser activates it just fine. But i cant get my lasers to stop dyeing. first i replaced the button batteries with a 4.5 v power supply. as i am sure you all know that doesnt work. so then i researched and found out i needed about 3v. so i built a constant voltage power supply using an adjustable LM317 voltage regulator. that didnt work. more research so i built a constant current supply also using an LM317. well that didnt work. my project also uses a relay in it so i thought i was getting a spike off the coil when the coil is denergized so i put a reverse biased diode across the coil leads. well the diode ran for 24 hours, then i switched the relay on and off a bunch of times and still all was fine. then i left it on for another hour came back and the laser was a very weak glow again anybody have any ideas what i am doing wrong. i am out of things to try

 

[Sigurthr]

Hmm. You definitely need a constant current driver, but did you check what current you are supposed to run the diode at?

What about heatsinking, you didn't mention anything about that either, you can't run diodes bare, not even 5mW ones.

 

[gary s]

well i dont know what the current requirement is but i only turned the adjustment up to where is was not a very bright red so was thinking i was low if anything. i did have it fairly bright for a few seconds at first but it ran fine for 24 hrs after that. it was in a brass module which seemed like a good heat sink.

 

[gary s]

i did find a loose lead going to the LD. think that would do it ????

 

[mattco2]

dude when your diode gets hot the current it wants goes up a cv driver just keeps the voltage constant not the current so they are probably dying from to much current

 

[RA_pierce]

If you're willing to skip making your own driver you can get this for $4: 650nm 5mW 3.2VDC 8x13mm, AixiZ
This laser module comes with a driver. All it needs is 3V.

Otherwise, as others said, you probably need current regulation.

 

[lasersbee]

i have been working on this project for a month. but i keep burning out my diodes.
my project is a photo switch using a 5mw laser as the light source. the photoswitch circuit works great and the laser activates it just fine. But i cant get my lasers to stop dyeing. first i replaced the button batteries with a 4.5 v power supply. as i am sure you all know that doesnt work. so then i researched and found out i needed about 3v. so i built a constant voltage power supply using an adjustable LM317 voltage regulator. that didnt work. more research so i built a constant current supply also using an LM317. well that didnt work. my project also uses a relay in it so i thought i was getting a spike off the coil when the coil is denergized so i put a reverse biased diode across the coil leads. well the diode ran for 24 hours, then i switched the relay on and off a bunch of times and still all was fine. then i left it on for another hour came back and the laser was a very weak glow again anybody have any ideas what i am doing wrong. i am out of things to try

I see that you are using a cheap Dollar Store Red pointer....
They are not intended to run constant ON... Hence the Button
Cells. There is almost always just a current dropping resistor
and no driver on the cheapest of those Toy pointers...

Save yourself some grief and get a bunch of these...
The work off 3.0V (2 AA Batteries)... or a Filtered Voltage
Regulated 3.0V Supply.

1 pcs mini 650nm 5mW 3V Laser Dot Diode Module Head | eBay

OR

http://www.ebay.ca/itm/1-pcs-mini-6...374?pt=LH_DefaultDomain_0&hash=item3f156496be
If they warm up you can easily add a heat sink...

With these you could use a standard 5V Fixed Positive Voltage
Regulator like the LM7805...


Jerry