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High Current Test Load Question

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x101xtreme

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Hi, I wanted to ask someone for help on how to build a high current test load. It seems like many of the test loads we have for red and bluray tend to get hot when running above 1 amp. Is it possible to build a test load capable of handling up to a couple amps continuously without overheating? Do I just replace the diodes and resistors with higher current ones?
 





I use some 1N540x diodes (3A capability) and a resistor capable of withstanding that kind of power (linked resistor is expensive for a resistor, but is 1 ohm, 3W, 0.5% tolerance). You can buy a lower ohm valued resistor and adjust your calculations as necessary. So if you have a 0.5 ohm resistor and it's a 2W variety it'll stand up to 4A of current.
 
I would suggest using a resistor smaller than 1 ohm though. Lets say you wanted to test with 3 amps: at that point the resistor will drop 3 volts, and dissipate 9 watts. Such resistors are available, and with bit of tolerance not that expensive either. But they do not represent the behaviour of a laser diode that can handle such currents well.

0.5 or 0.33 ohm would be a better choice, but the disadvantage is that you need to multiply the voltage across it by 2 or 3.
 
Hey SHIN, do you happen to have a circuit diagram for the test load you constructed? I know that you used these parts:

7 of 1N5404 (3A, 0.7V voltage drop)
4 of 2W 1ohm resister(=1 of 4W 1ohm resister)
1 of 2W 2.7Kohm resister

but I just wanted to make sure how to connect them. Is everything in series? Or are there parts of the circuit which are wired in parallel?
 
Do as you see fit, but 1 ohm of dynamic resistane doent fit wth real life diode current vs voltage graphs. Those constructions were a good match for what the lower powered bluray and red diodes do, but with the 445s its a bit out of line.

Not that it matters much to a good current source though - that'd output the same current regardless of the load, even if that lot is a monkey wrench with croc clips attached ;)
 
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