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09-16-2009, 06:54 PM #1
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CRXDelSol
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Need help with current and resistance

Hello,

Recently I bought this laser kit on Ebay:

300mW+ 650nm Red High Power burn Laser Diode Module Kit - eBay (item 280393602910 end time Sep-11-09 21:27:47 PDT)

It came well shipped, all parts were in the package.
Now I have soldered everything on the circuit-board, and now I am trying to find an adaptor which I can use for testing.

However, I don't want to kill the diode, so I wanted to ask for some advice...
I don't know much about resistors and currents.

On the example page which includes the schematic, it shows an example current of 417mA with 3ohm resistance (adjustable @ pot).

I = 1.25 / R

I = current, R = resistance

I can use 6 to 20 Volts.

My questions:

1. How much difference does it make when I use 6 or 20 Volts?
2. In what kind of way will this have influence on the input mA + ohm's?
3. Can I use a 12V - 350mA adaptor? I guess I then have to set the pot to 3.57 ohm. [ 1.25 / 0.350 = 3.57 ].

Just for extra information, the title on the schematic shows:

"Max 463mA Constant Current LD Driver Kit
Input Voltage 6 - 20V"

Thank you.

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09-16-2009, 07:07 PM #2
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ElektroFreak
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Re: Need help with current and resistance

Quote:
 Originally Posted by CRXDelSol On the example page which includes the schematic, it shows an example current of 417mA with 3ohm resistance (adjustable @ pot). I = 1.25 / R I = current, R = resistance I can use 6 to 20 Volts. My questions: 1. How much difference does it make when I use 6 or 20 Volts? None as far as output. The regulator in the circuit (little black box with three pins and a metal tab) will convert any excess voltage to heat, so the higher the input voltage, the more heatsinking the regulator will require. 2. In what kind of way will this have influence on the input mA + ohm's? No influence. As long as you have built the circuit correctly, the output should remain the same at any input voltage between 6 and 20V. 3. Can I use a 12V - 350mA adaptor? I guess I then have to set the pot to 3.57 ohm. [ 1.25 / 0.350 = 3.57 ]. I would find an adaptor that provides more than 350mA, 500mA-1A (1000mA) would be best. The kind of diode in your kit will last longest if you set the driver's output at 325-375mA Please help me out, I am not realy into currents and Voltages etc. Just for extra information, the title on the schematic shows: "Max 463mA Constant Current LD Driver Kit Input Voltage 6 - 20V" Thank you.
blah blah max characters blah
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09-16-2009, 07:12 PM #3
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CRXDelSol
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Re: Need help with current and resistance

I do have an adaptor with more mA output, 600 for example.
But I don't know what the output mA will be then.
That depends on the pot right?
So if I put 600 mA directly on the driver, what will be the best value for the pot then?

(Again, sorry for my low level of knowledge about electricity...)

09-16-2009, 07:14 PM #4
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ElektroFreak
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Re: Need help with current and resistance

You'll need to build and use a test load to set the driver. You hook the load up to the driver first instead of the laser diode, then you set your current, and then disconnect the test load and connect the laser diode.

Also, this thread has TONS of info to help out a new person such as yourself: Meta Topic : Pinout & Performance of actual LD
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Laser Resources (for n00bs and veterans alike!)

Sam's Laser FAQ (The Laser Bible)

http://www.repairfaq.org/sam/laserfaq.htm

RP Photonics Encyclopedia of Laser Physics and Technology

http://www.rp-photonics.com/encyclopedia.html

ULTIMATE DIY PROJECTOR REFERENCE

http://nqlasers.com/scannerreference...itle=Main_Page

SUCCESS is the best revenge.

Last edited by ElektroFreak; 09-16-2009 at 07:17 PM.

09-16-2009, 08:22 PM #5
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CRXDelSol
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Re: Need help with current and resistance

I have found that I need the following parts for a test/dummy load:

4 1N400X diodes and a 1 Ohm resistor

Then I have to find those 4 diodes first.
I will go look for it.

09-16-2009, 11:17 PM #6
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ElektroFreak
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Re: Need help with current and resistance

1N4001 will do fine. You can get them very cheaply from Radio Shack (or any electronics supplier)
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Laser Resources (for n00bs and veterans alike!)

Sam's Laser FAQ (The Laser Bible)

http://www.repairfaq.org/sam/laserfaq.htm

RP Photonics Encyclopedia of Laser Physics and Technology

http://www.rp-photonics.com/encyclopedia.html

ULTIMATE DIY PROJECTOR REFERENCE

http://nqlasers.com/scannerreference...itle=Main_Page

SUCCESS is the best revenge.

09-17-2009, 12:50 AM #7
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lasersbee
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Re: Need help with current and resistance

Don't forget....
you can get 10pc FREE 1 Ohm 1/2 Watt resistors here on the Forum...

http://laserpointerforums.com/f39/fr...ors-42409.html

Jerry
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