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Old 01-06-2017, 07:11 PM #1
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Default Adjustable Test Load

So I've dabbled with adjustable test loads before, using discrete components. However due to the method of operation the actual V-drop would take some time to actually go into effect, preventing it from reproducing the actual way laser diodes function... Aka, It'd be super high resistance for a split second, and then it would come down to the actual drop you desire.


So, as an alternative...

http://tinyurl.com/gplg4f6

What looks an awful lot like this circuit diagram you might ask?

An LM337 negative voltage regulator.


Since it uses a PNP transistor as its pass element it more accurately represents the way laser diode drops work, at least, in theory.

If anyone has a switching driver, an oscilloscope, the parts, and some extra time I'd be super appreciative if someone could test out my theory! I don't have any switching drivers on hand currently otherwise I'd try it out myself.

If anyone wants to comment, on whether they think this would work or is complete sillyness then please do!


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Old 01-08-2017, 05:43 PM #2
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Default Re: Adjustable Test Load

I can't tell if you're making a lot of newb mistakes, or I'm just misunderstanding your diagram based on lack of labeling.

Either way, it appears as though you're trying to make an active load. A few people have tried this, and the problem is getting the response times down to the level of a silicon diode, as well as stabilizing the design enough to prevent oscillations under all conditions.

It works on paper, but when you build them, they tend to oscillate. I'm sure with enough patience and expertise you could stabilize it, but a row of silicon diodes is just SO much easier, and a guaranteed approximation from the start.
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Old 01-08-2017, 07:54 PM #3
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Default Re: Adjustable Test Load

Yeah, I figured that was what the issue is. I keep wrestling with whether or not it's worth it, and I keep coming back to, no, it's really not. And the circuit diagram isn't really well labeled, but it's basically an approximation of what's inside most linear voltage regulator IC's.

I thought maybe using a 3 terminal voltage regulator would solve some issues, making it easier to use (and maybe solve the oscillation problems?) but eh, yeah, silicon diodes are probably the best solution. After all, "KISS" right? :P

Basically I was just thinking outloud.
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