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LPC-815 Led

larry

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Sep 27, 2010
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My LPC-815 just went led. It have been working fine for the past 1 week. My driver was base on LM317 DDL circuit(I just add additional LM317 in front to lower voltage). My driver is powered by a switching mode power supply 12v 1.7A. Using 2 LM317 for my driver. The first LM317 lower the voltage to 7.5V and the next LM317 to lower the current to 380mA(I wonder is it to high for LPC-815). I mount the aixiz module to a OdicForce Alloy Laser Module Holder / Heatsink with 120mm fan at the side to keep cool. I wish to know what cause my diode to led.

1. switching mode power supply?
2. 380mA too high?
3. driver build wrongly?
4. others?
 





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If you dropped 12V to 7.5V with the first LM317, how hot did it get? Did you have it heatsinked?
 

larry

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Both my LM317 is equipped with a decent heatsink with a dimension of 35mm x 25mm x 10mm (WxHxD). I trying connect it to a test load and see how hot the heatsink can go with a 120mm fan cooling it down. After leaving it on for 5min, it is just warm.
 
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Oh ok, that's a big heatsink and sounds good for this voltage drop. Hmm, did you have a pot in the circuit? What about capacitors? Both can cause problems, I killed 2 LOC's using a pot, then switched to just a 3 Ohm resistor. Post some pics and draw your circuit, this will help a lot.
 

larry

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I do not really trust pot as it might fail and bye bye diode so I prefer to set it at a fix current. =D This is my circuit and thanks for the speedy reply. =D

LM317components01.jpg
 

Morgan

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Feb 5, 2009
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Bare in mind that they sometimes do just die. LOC diodes are particularly vulnerable during the extraction process and can be damaged easily without knowing it at the time. They are also susceptible to back reflection. What lens are you using? If it's an uncoated one then this could help towards failure as it's pretty close to maximum output at 380mA, (~420mA is considered max).

Your driver setup does sound unconventional but without knowing exactly how you've got it setup it would be hard to comment. Usually you would use a lower voltage supply but it seems you've thought of that and the diode was running fine before LED. How have you set your current? What LM317 circuit did you use? [EDIT: Circuit posted as I was writing] Do you have any pictures of the setup?

M
:)
 

larry

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I am using a Glass Collimating Optics lens so I guess it is an uncoated lens. So I am better off for a AR coated glass lens for laser focusing modules(red/635-670nm) from Modwerx?
 

Morgan

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You are always better off with an AR coating at the higher powers. To tell if yours is coated you can look at the reflection of natural, (or normal household lighting), and see if the reflection shows a certain colour. Usually AR coatings for red will appear blueish. They are not expensive either. Aixiz or similar should cost around $10.

For the electronics part of your build you will have to wait for more expert opinion as it's not my forte.

M
:)
 

larry

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What a surprise, my glass lens appear to be blueish compare to the acrylic which appear to be clear white. So if my glass lens is coated for red then this will not be the factor that cause me own a led diode. =D
 

Morgan

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If you're seeing the blueish reflection then it certainly sounds to be AR coated and therefore a back reflection can likely be ruled out as the cause, yes.

One thing down, a few others to try... But, again, it could just have died. 380mA CW, although not what we might consider maximum, is still a fair way above the manufacturer's stated safe rating. The LD may have passed their QC but not stand up to the frankly unfair working conditions and bad treatment we subject them to, (there must be a LD union somewhere?). If no-one can find fault with your driver, (As I said, I'm no expert, but I would still advise going to a lower voltage power supply and lose one of the LM317s ;) ), and all else is found to be fine then just accept it as part of the hobby and install a new one.

Before blithely replacing your diode however, you should check all your connections and solder joints. If, for example, one of the diode pin connections were to go open circuit for an instant and then reconnect; this will mean almost certain death for your diode as the protection capacitor charges fully during the disconnect and dumps everything through your LD when reconnected. This won't help your deceased diode but may prevent the next suffering the same fate.

M
:)
 

larry

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Anyone can tell me if my circuit is good as a driver? Am I better off with a non regualted power supply and regulated it with LM317? This is the lowest power source(12v 1.7A) I can find. I do not intend to drive using battery because I am trying to refrain from bring my laser out for show as any laser >5mW is ....... at my side.
 




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