High Current Test Load Question

[x101xtreme]

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?

 

[Bionic-Badger]

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.

 

[SHIN]

Hi. x101xtreme.

I hope this may be helpful..

http://laserpointerforums.com/f51/dummy-load-high-current-2a-test-load-3a-52372.html

 

[Benm]

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.

 

[x101xtreme]

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?

 

[Toaster]

Or you could just get this resistor here

And these diodes here

Works like a charm

 

[SHIN]

The circuit diagram was originally from HIMNL9 at this thread:

http://laserpointerforums.com/f38/test-load-44348.html

Thank you. HIMNL9.

SHIN

 

[Benm]

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