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power supply suitable for testing diodes

rustynuts

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I am looking for advise, I'm thinking of using only my HP E3614a power supply to power a 445nm 1w diode for first light.
I thought that I should use the HP because it has a ten turn current adj pot.
Is this suitable to slowly up the current and not spike the diode? Or do you guys think that I need to add a extra current regulator circuit in series like the lm338 or lm317 for safty for the diode? Are dedicated drivers any safer for ramping up these diodes?
 



Immo1282

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What a laser diode wants in terms of power is current-regulated clean power (low noise) without a really significant current spike at the start. If your HP unit can operate in constant current mode, I see no reason why you'd need a separate current regulator. Is the HP supply a linear supply? This can be fine - but a large output capacitance isn't always ideal as it can pull a huge spike of current at poweron to charge the output cap if it's designed clumsily.

If you want to verify this - build (or buy, but building it could well be quicker depending what parts you have lying around) a test load using a handful of diodes and a shunt resistor and characterise the transient spike when your HP unit powers on. I've attached a "schematic" for one that I have used for setting and measuring small drivers. Not sure who made it but I found it on the forum a couple of months ago...
 

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rustynuts

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Thanks
I only use linear power supplies for my lab, I have over 20 different supplies I think it is a addiction and cant help myself I just cant stop buying broken american made ones and fixing them. Yea, HP has designed some lemons. So I need to test the supplies overshoot, I will and also look it up in the service manual and see if it is still in spec.
 

paul1598419

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You might also want to look at the pot's noise level. A noisy pot can cause current spikes as you increase the current while the diode is lasing.
 

rustynuts

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Because all of my power supplies are used, 70s-2000s
You read my mind,
what would be the best way to clean them?
Is there any good way to? If not I Am willing to replace the pots with better ones if they are any out there. any suggestions?
 

paul1598419

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I would suggest you clean the pot, but since many multi-turn pots are sealed that might not be easy to do. I have always used an aerosol cleaning solution on pots. There are many different types, but ones that leave a slight lubricant seem to work best.
 

rustynuts

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I will clean the pots one way or the other.
This power supply has the option to be externally controlled with a 0-10v source.
For now I am in no hurry, The fun part is learning how anyway.

ok, guys has anyone done this: use optical rotary encoders to control a digital to alalog source, maybe then use that to externally control the big power supply. This may give me more control and no noise compared to the mechanical pots. also maybe add a de bounce circuit too,
and as a added bonus it meaning the control panel, can remain in place and i can choose the correct supply for the diodes needs
If you all think this a wild goose chase then ,
I may not try it.
 

Immo1282

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Seems a little over complicated perhaps - but I see no reason it wouldn't work if you set it up properly. Probably at the point of diminishing returns for what you're trying to do.

Probably the best thing to do would be to hook up a scope and verify to see if you even need to worry about the pot - Could be that after a clean everything's perfectly suitable as it is?
 




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