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445nm LD Voltage?

Fiddy

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Hey,

One of my 445nm 1.2W lasers has stopped working and im trying to figure out why.

I measured the voltage across the LD being 7.6VDC isn't it meant to be 4.2~4.5VDC? Would that mean the driver is stuffed?

Also how would i test the LD?

Cheers!
 





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What driver?

A boost driver trying to drive a LD that failed open-circuit would explain your findings.
 

DrSid

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One way to test LD is connect it to directly to battery with 4.5V (or 3xAA, AAA). You must pay attention to static discharge, the diode must be properly heatsinked, and you should short-circuit the battery with fingers for a moment as charge can allegedly buildup inside the battery which could kill the diode. From my experience the diode survives even bad polarity for several seconds without any damage (this is however totally not true with drivers, which will try to pump preset current through the diode).
 

Fiddy

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short circuit the battery with fingers? don't think it will be much of a short cause last time i checked skin was an insulator?

so what your saying is direct drive it with 3 AAA's in series?
 

DrSid

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I get around 20k ohm through your fingers. This will depend on individual, and condition (for example my mom has like 10 times bigger resistance then most people, and swat or moisture can lower the resistance 10 times lower). It's just enough to suck any charge and not to damage the battery in any way. Anything should work, but since fingers are
'at hand' there is really no need for anything else.

Check this thread I made the day I got my first diodes. The risks are discussed there, but many people here did or do drive those diodes directly.

http://laserpointerforums.com/f65/445nm-dilda-direct-drive-just-fun-55343.html

Good think is you can just hold the wires .. no need to soldering. On the other hand, lots of drivers require soldering, as even short time of open output circuit will kill the driver. Also, as I said, most drivers will kill the diode if you use wrong polarity. Static discharge is major risk.
 

Fiddy

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ahh ok, can you tell me why the driver will die if it operates with no load?
 

DrSid

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It's not true for all drivers .. but it is true for example for FlexDrive V5, which is very popular around here. Without load there is no current .. ie the current is too low .. so it increases voltage .. but the current is still zero .. so it increases the voltage over limits. It is the most common case of non-working 445nm laser, diode is usually OK.
 




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