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10-25-2010, 11:22 PM #1
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LiquidLife
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Question- Simple circuit to test diode

Hey all,

I was wondering if I use the information provided in the datasheet below for a 250mW laser diode, if I could just create a simple circuit insuring that the voltage and current was appropriate, just to test it out...

(Simple circuit includes 4x AA batteries in series with - + leads, 2x 51ohm resistors in parallel to = 25.5ohms total resistance, 1x 250mW diode)

This configuration should give the laser diode an estimated 2.685V, 130mA. What I don't understand though is that 2.685V x 0.130A = 0.349W

Can someone chime in and make corrections where needed?

Also can someone explain what threshold current is, and all those other little symbols and stuff?

Last edited by LiquidLife; 10-26-2010 at 06:17 AM.

10-26-2010, 06:04 AM #2
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LiquidLife
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Re: Question- Simple circuit to test diode

Okay, so I looked up threshold current, and it's what I thought it was; minimum current, basically.

What I'm confused about, is why the Operating current AND operating voltage = 325mW

10-26-2010, 06:08 AM #3
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Toke
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Re: Question- Simple circuit to test diode

Laser diodes are rated by output power, as efficiency vary (50-20%) the input power will be significantly higher.

(I have not checked your calculations, but the 6V from your batteries should be distributed between resistors and diode.)
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Last edited by Toke; 10-26-2010 at 06:10 AM.

10-26-2010, 06:13 AM #4
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LiquidLife
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Re: Question- Simple circuit to test diode

I see, thanks that helps.

So as far as testing the diode safely, this simple circuit should work?

Quote:
 Originally Posted by Toke Laser diodes are rated by output power, as efficiency vary 50-20% the input power will be significantly higher.

10-26-2010, 06:14 AM #5
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LiquidLife
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Re: Question- Simple circuit to test diode

I'll write out my calculations

10-26-2010, 06:28 AM #6
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LiquidLife
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Re: Question- Simple circuit to test diode

As you can see the resistor should be about 27 ohms for 2.5V and .130A for the laser diode.

10-26-2010, 08:56 AM #7
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Toke
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Re: Question- Simple circuit to test diode

It looks workable to me, at least for testing.

Your two 1/4W resistors should be able to handle the effect, the diode will get hot, so you better put it in a heatsink or just run it for a sek at a time.

The diode voltage drop is not completely static, but rises a bit with current and drop with temperature. Guess you know that as you are calling this a test setup.
__________________
100mW Odicforce kit.
App. 300mw MiniMag
App 120mW labby
Fan cooled 400mA 12X 405nm flashlight

532nm 150mW Labby.
532nm 50mW in flashlight

1.2W 445nm Yobresal
Basic laser building guide.

10-26-2010, 07:48 PM #8
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LiquidLife
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Re: Question- Simple circuit to test diode

Thanks!

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