Old 10-26-2010, 12:22 AM #1
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Default 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 07:17 AM.
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Old 10-26-2010, 07:04 AM #2
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Default 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
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Old 10-26-2010, 07:08 AM #3
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Default 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 07:10 AM.
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Old 10-26-2010, 07:13 AM #4
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Default 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 View Post
Laser diodes are rated by output power, as efficiency vary 50-20% the input power will be significantly higher.
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Old 10-26-2010, 07:14 AM #5
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Default Re: Question- Simple circuit to test diode

I'll write out my calculations
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Old 10-26-2010, 07:28 AM #6
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Default 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.



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Old 10-26-2010, 09:56 AM #7
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Default 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.
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Old 10-26-2010, 08:48 PM #8
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Default Re: Question- Simple circuit to test diode

Thanks!
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