Old 01-22-2011, 02:06 AM #1
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Default A new member to the laser community having some issues... please assist

Hi all

firstly let me apologize for my poor English..

anyways here's the deal:

I bought this from ebay: 250mW 405nm Blu-ray Blue-Violet Laser Diode Module DIY - eBay (item 230575773675 end time Feb-18-11 03:27:49 PST)

1. Could i measure the diode power like this:


I know that laser power is usually measured in head generated or something like that. There's device and you point at it and you will see how much power.

As much as i know about physics i know that power = voltage*current as in P=UI

now i have measure regular lightbulbs in this way with the multimeter by placing the multimeter inbetween the + and lightsource. by reading the multimeter and multiplying it by the amount of voltage there is on the + and - on the lightsource i get the power in watts. If i was using a 1.5V battery and the current was 3A then the power would be about 5W.

Could i apply the same principle when measuring this laser diode? As i could see from the pictures the driver had a potentiometer so i could theoretically adjust the impendance and thereby the power on the diode. my problem was how to monitor the changes.

Also any information on this ebay item would be greatly appreciated.

2. second question is about batteries. as you can see the diode on that particular set is powered by 4 AA batteries. Now i bought a 9led mini flashlight for the host and it had a housing for 3 AAA batteries. Since i read somewhere that 4.5V is the minimum that a blue laser requires i was stuck.
I thought that maybe using 3 10440 AAA 3.6 each and 10.8V total would be better. Is there a possibility that i will overburn my diode by using so much more voltage because as the voltage increases so should the power according to above.

Hope i could make myself clear and you understand my problem.

feel free to ask if you couldn't understand my point

thank you in advance!

Gustav


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Old 01-22-2011, 02:21 AM #2
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Default Re: A new member to the laser community having some issues... please assist

Welcome to LPF. If You place a DMM as indicated in your drawing you could check how many ma the diode is getting. That could be used as a rough estimate of how many mW's the diode is producing, but depending on how efficient the diode is will effect output. Connecting a meter this way could cause the diode to fail unless you have a rock solid connection. You need to know the drivers input limit to select alternate batteries. It appears to be a linear driver, so it will eat up some of your voltage say maybe ~2v so you need at least 6.5v to cover this loss. also you will need to short the drivers output before you hook up your meter or diode
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Old 01-22-2011, 02:35 AM #3
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Default Re: A new member to the laser community having some issues... please assist

You need what is commonly referred to as a test load. It is a series of normal diodes to simulate the laser diode along with a 1 ohm resistor. Reading the voltage across the resistor will tell you how much power your driver is pushing. Searching for Blu-ray test load will get you plenty to read on the subject.

I do not suggest reading current in the way you picture there. As Coherent said you run a very likely risk of killing that diode. Also reading current that way will not leave much room for error if you accidentally turn the pot too much, that could be the end to your expensive diode.

Also, search for SF-AW P-I-V graphs. That will help you choose a current that is safe for the diode.

Good luck!
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Old 01-22-2011, 03:06 AM #4
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Default Re: A new member to the laser community having some issues... please assist

okay

thanks first for the quick replies

as i understand the best way for me would be to make a test load. how many diodes do i need? i've see some with 10+. why so many?

also could i refer to this: http://laserpointerforums.com/f38/sf...ead-44858.html when measuring with multimeter?

as i see from that graph that i could use normal 1.5V AAA x 3 not 3x10440 with the diode right? or is it better if i go with the 10.8V version i spoke about in my first post?

even if i used 3 normal AAA's with 4.5V total and i took the reading on the multimeter at 0.05A i would be getting about 250mW yes?

Also i would like to know how can i find out the min and max voltage my driver can take?


thank you again!

Last edited by contrast; 01-22-2011 at 03:14 AM.
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Old 01-22-2011, 04:47 AM #5
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Default Re: A new member to the laser community having some issues... please assist

You won't have enough voltage to run your diode with 3 AAA's. The Diode needs ~4.5v, but you must take into account how much you lose to the driver. The driver looks to eat up around 1.5v to 2v.
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