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Old 01-01-2011, 03:21 AM #1
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Default Using a burned-out LD as a test load?

Hey, I'm just wondering if an actual burned-out LD (LED? )would make a more accurate test load than a traditional homemade diode one.

My homemade multiple diode/resistor one is about 20mA off when it comes to the actual current.


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Old 01-01-2011, 12:52 PM #2
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Default Re: Using a burned-out LD as a test load?

I wouldn't help much, diodes behave pretty much like diodes, only the voltage drop can be different. That 20mA error, is it an offset or slope error? 20 mA on a 50mA current is a lot but on a 400mA current it's within the resistor's precision for a 5% resistor.
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Old 01-02-2011, 03:21 AM #3
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Default Re: Using a burned-out LD as a test load?

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I wouldn't help much, diodes behave pretty much like diodes, only the voltage drop can be different. That 20mA error, is it an offset or slope error? 20 mA on a 50mA current is a lot but on a 400mA current it's within the resistor's precision for a 5% resistor.
Yeah, I'm testing it at typical red DVD diode current (~150-350mA).

So a burned out diode would also have this discrepancy at this kind of current?
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Old 01-05-2011, 01:20 AM #4
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Default Re: Using a burned-out LD as a test load?

I've noticed that LED'd laser diodes have slightly lower forward voltages at a give current, but the difference is not very large. As long as you are working with constant current drivers they will make fine dummy loads in most cases.

The downside is that they might not be reliable: diodes that have failed from COD will likely be good dummy loads, but if they failed from anything else they might not be.

As far as dummy loads go there are plenty of options. The typical string of diodes and shunt resistor is extremely reliable, but i have used power LED's (leftover luxeon stars etc) too, since they give a nice visual feedback of what is going on and are more rugged than laser diodes in case of a mistake.
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Old 01-06-2011, 04:17 AM #5
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Default Re: Using a burned-out LD as a test load?

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Originally Posted by Benm View Post
I've noticed that LED'd laser diodes have slightly lower forward voltages at a give current, but the difference is not very large. As long as you are working with constant current drivers they will make fine dummy loads in most cases.

The downside is that they might not be reliable: diodes that have failed from COD will likely be good dummy loads, but if they failed from anything else they might not be.

As far as dummy loads go there are plenty of options. The typical string of diodes and shunt resistor is extremely reliable, but i have used power LED's (leftover luxeon stars etc) too, since they give a nice visual feedback of what is going on and are more rugged than laser diodes in case of a mistake.
Yeah, maybe I'm being a little too demanding with the diodes/resistor dummy load (+-20mA). I'll just stick with that for now.
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