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How is this possible? laser emmits light with no power going through.

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bhwollen

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Ok, so I have a labby using a 12v wall power supply. The setup is; Positive goes into lm317 then uses a 0.62 ohm resistor then into the diode. should be a little less then 2A. I have the negative pin bridged with the case pin and the way i power it touching the negative power to the heat sink. All works well, but after i disconnect the negative wire. there is a tiny blue spot comming out of the laser. I dont understand :confused: makes no sense to me? any input? Ill try to upload pics later.
 





Do you have any capacitor in your driver?
It is discharging into the diode, but it's not enough current to make it lase, so it
just glows faintly as it emits spontaneously.
 
Nope. like i said lm317 .62 ohm.
anselm said:
Do you have any capacitor in your driver?
It is discharging into the diode, but it's not enough current to make it lase, so it
just glows faintly as it emits spontaneously.
Click to expand...
 
The wall wart itself has several capacitors. Take both leads off, and the glow should go away.

edit: oh, and your regulator isn't rated for that kind of current. You're pushing your luck by running it that high. Is your wall wart even rated for 2A?
 
It happened to me too, using a bench PSU with only the VCC connected to the diode, when I touch the black wire the diode light up :thinking: dunno but never affected it in anyway.

PS: No caps
 
No, there aren't. Not on the output at least.

And.. the wiring was:
+ bench output : + Diode Input
- bench output (gnd) : not touching anything
My hand : - Diode input (gnd)
 
well, in regards to OP,
Depends really on the wallwart that your using. the older iron core ones usually dont have any capacitors, and output raw fullwave DC.
The newer SMPS style almost always have filter capacitors. (the smaller, lighter solid state wallwarts)

And I did a setup like yours before, Leo.
I was using an old HP lab supply (those old ones with hand drawn PCBs and with filter capacitors) and personally didn't have this happen to me.

I doubt it will be residual charge in the capacitors in my supply would have done it too.
after the bleeder resistor, whatever little charge is left isn't probably enough to even cause the diode to conduct. (or laze for that matter).
So Im not quite too sure why it would glow like that if it werent for those reasons.

EDIT: Here is the PSU I was using. but I didn't note any of this behavior.
Its old yes, but it has a very stable output, and takes anywhere between 200mS - 1S to fully drain its capacitors to a few millivolts after shutoff without a load. (depending on its voltage settings, etc)

PSU.jpg
 
Last edited:
Hmm I recalled that when I touched the ground with my foot it got more strong. :D
:p
 
All I can say about this, I have two capacitors in my 445, one 2200uF 16V on the input
side of the driver and one 1200uF on the output side.
After I turn it off, the LD still glows (not lasing) for about a minute before it turns off completely.
 
Leodahsan said:
Hmm I recalled that when I touched the ground with my foot it got more strong. :D
:p
Click to expand...

I havent tried that, when I was testing it out with the PSU, it was hands off for me.

I did scope the output once, when I touch the chasis the output rings to a couple hundred mV (although very unstable and drops/falls quickly in <5uS periods)

I thought this was just interferance of myself touching stuff.
 
@Cyparagon
I didn't took it apart. I am no electronic master but the guy who selled it, says there are no capacitors on the output. Anyways, I said the diode was lighting up without the " - " connected to the PSU.
 
That doesn't mean there wasn't a ground loop of some sort. And I've never seen a bench supply without caps.
 
Leodahsan said:
Hmmm.. Is it possible to form a ground loop with my body, right?
Click to expand...

indeed it is possible to have a ground loop form with your body. I agree about the capacitors as they can hold a charge for quite some time!
Never done it with this low a voltage.

The PSU may not be fully grounded or is faulty?


You need to be VERY careful to always ground yourself when working around expensive LDs!
 
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