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Old 06-23-2011, 08:27 PM #1
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Default Laser not emitting light

Hey All,
I have built a DDL driver with a 5 ohm (2x10 in parallel: measured value=5.4) resistor and hooked it to my 405nm diode (New 250mW+ 405nm 6X High Power Blue-Violet Laser Diode - eBay (item 270750778133 end time May-31-11 19:19:53 PDT)), however no light comes out. My battery is a 9-volt, and it measures 9.48-9.50 without being attached to the circuit, but it measures 9.33-9.34 when it is attached, leading me to believe current is going through the circuit. Is my diode broken? If not, what is wrong with it?

Thanks to everyone in advance.


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Old 06-23-2011, 08:39 PM #2
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Default Re: Laser not emitting light

Did you discharge the caps in your DDL driver? If you didn't the diode may have fried.

If you haven't I'd build a test load and check the current coming from the driver. 250ma is pushing it for a 6x diode IMO. I have mine running on 170ma.
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405nm: 170mw 6x SF-AW 210 Guidesman host (thread)
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Old 06-23-2011, 08:43 PM #3
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Default Re: Laser not emitting light

I would assume the cap wasn't charged at all when it came from radio shack, but maybe it was.... :c

I didn't see any sparks or anything, and since it is 100 mfd does that make it unsafe to discharge across my tongue?

Can I try running it with 10 ohm instead? The listing also said that its minimum recommended current is 190 ma

Thanks for your help...
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Old 06-23-2011, 10:38 PM #4
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Default Re: Laser not emitting light

It wouldn't have been charged when you bought it but if you power the driver before attaching the diode you need to discharge it. It won't always kill the diode if you forget but it quite often does. They will self discharge eventually but the fastest way is to just touch the leads to the diode together. 250 is about the top end of the range for 6x diodes IIRC. 125 would be fine. I guess I was a little conservative with my build since it was my first build but it's still going strong 8 months later. I also used the SF-AW210 diode which is a little less tolerant than the GGw 6x at higher currents.

I'd still build a test load and test your driver. You'll probably have to either get the 1 Ohm 1W resistor somewhere other than radio shack (since they don't have them) or go up to a 10 ohm and use Ohm's law to figure out how much current is flowing across it. I *think* if you multiply the measured current by 10 you should get the right result but I'm not sure if that'd work. If I have time tonight or tomorrow I can make a quick DDL driver and test load on my bread board with a 10 ohm resistor and compare it to a 1ohm.
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405nm: 87mw PHT-803T in hotlights (thread)
405nm: 170mw 6x SF-AW 210 Guidesman host (thread)
445nm: 710mw Guidesman host
635nm: 4mw pen host (thread)
660: 190mw LPC-815 Guidesman host
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Old 06-25-2011, 12:46 AM #5
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Default Re: Laser not emitting light

Just an update for anyone who read my previous post. I did a test on my breadboard using an LM317 based driver and 6 1N4001 diodes as a test loadto simulate a 405/445 diode. The driver was set up with 3 10 ohm resistors in series which gave ideally would have given me 41.6ma. It was powered by my bench supply set to 9.5v.

With the test load connected to the driver and my DMM set to measure mA I measured 43mA at the LD+ and - connection well within the tolerance of the resistors. If you use something other than a 1ohm resistor you'll have to divide the results you get by the resistor value in ohms to get the correct result. Remember 1 mV across a 1 ohm resistor is equal to 1mA.

resistor mV across mA

1 Ohm 43.4 43.4
5.1 Ohm 217 42.5
10 Ohm 418ma 41.8

The results are almost identical and and well within the 5% tolerance of the resistors. The 10ohm gave almost the exact theoretical value of 41.6 mA.
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My builds:

405nm: 87mw PHT-803T in hotlights (thread)
405nm: 170mw 6x SF-AW 210 Guidesman host (thread)
445nm: 710mw Guidesman host
635nm: 4mw pen host (thread)
660: 190mw LPC-815 Guidesman host
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