Old 04-25-2012, 11:11 PM #1
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Unhappy So confused.... help please?

Hi everyone! So i was working with a new PHR805-T diode and a custom built LM317 regulator. I tested the regulator for 15 minutes, and there was no current fluctuation. I set the regulator to 110mA, and had 7.5 volts coming in. So i plug the diode in, set it in the heatsink, turn it on, and it's awesome. Not even 10 seconds in, the brightness dimmed. It blew. Can anyone help me figure out why?? I only have one diode left and I can not afford to wait another 2 weeks for another to ship, as i have a project due in 9 days. Thanks in advance for the help.


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Old 04-25-2012, 11:27 PM #2
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Default Re: So confused.... help please?

You're supplying an LM317 with 7.5V? For that PHR try at least 8V try it with your old diode just to be sure that that is the problem
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Old 04-25-2012, 11:31 PM #3
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Default Re: So confused.... help please?

Could be that your diode was inefficient and the current blew it. Try 95mA, IIRC that's the safe current for PHR diodes. Also, if you're using a capacitor in the LM317 driver don't forget to short the leads before connection your diode. Check the wiring on your driver and make sure everything is connected how it should be.

If you're in Canada I can send you a PHR for free in the unfortunate event that both your diodes blow.
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Old 04-26-2012, 12:51 AM #4
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Default Re: So confused.... help please?

ARGLaser, thanks for the offer but i am in the united states. AnthoT, if i need 8 volts and was only using 7.5, why would the diode have flashed like that? And also, i want to at least be able to burn a peice of electrical tape or light a match when i present, so is 95mA going to be enough? Please correct me if i am wrong, but P = IxE, so with those numbers it would output .76 watts... and it should be 100-120 mw..?
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Old 04-26-2012, 12:55 AM #5
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Default Re: So confused.... help please?

Quote:
Originally Posted by craigrose View Post
ARGLaser, thanks for the offer but i am in the united states. AnthoT, if i need 8 volts and was only using 7.5, why would the diode have flashed like that? And also, i want to at least be able to burn a peice of electrical tape or light a match when i present, so is 95mA going to be enough? Please correct me if i am wrong, but P = IxE, so with those numbers it would output .76 watts... and it should be 100-120 mw..?
The batteries voltage could have dropped quickly as it wasn't enough in the first place, so 8V is not a bad place to start, like ArgLaser said you should also try with 95mA
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Old 04-26-2012, 12:56 AM #6
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Default Re: So confused.... help please?

Most of a laser diode's input energy is wasted as heat so you can't multiple input current by input voltage to get output power unless you know the efficiency curve for that exact particular diode.

That being said 95mA will burn almost as well as 110ma, the change would be very small.

One thing you failed to mention was heatsinking. Laser diodes cannot be run outside of a heatsink for more than a second or two. Make sure your diode is pressed in to a module, and even then don't run it for more than 10sec unless the module is in a heatsink and you are using thermal compound.
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Old 04-26-2012, 12:58 AM #7
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Default Re: So confused.... help please?

and also, i'm using an adjustable power source that i built to connect to a wall outlet. does that change anything? The power source is very reliable.
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