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FrozenGate by Avery

Problems with diode, What i did wrong?

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eyeballpaul

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Oct 13, 2009
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Well, before i got my heatsink for aixiz module, i decided to make a quick test for the xj-A140 diode. Due to lack of the portable driver yet, i made a circuit with an incandescence lamp and an stabilized DC power supply. The power supply has a voltage amplitude of 0-15V and constant current of 1A (but i measured 1.25A coming out of it). The Incandescence lamp i used to reduce the circuit current (stupid way, but had no fitting resistors near at hand and it was late to go buy them, i had a very strong desire to see the blue light). This made a current of ~0.3A. I set voltage to 5, and connected a diode (in aixiz module) for a few seconds. It worked, but light was too dim. So i added a second lamp in parralel. Current increased to ~0.55A. Another few 2-second tests, diode shines bright at first split of a second, then becomes dim. And so some times. I thought that lamps was the reason, taking current from diode. Dreaming of a bright blue beam i decided to make a direct drive to a power supply (1.25A, 5v to xj-A140). For a few seconds of course, to not to overheat the diode. Few quick tests. Light was very bright. Aixiz module was pretty warm, i waited till it cool down and turn on again - again dim light. After 2 minutes of waiting, new test, it makes a bright second and dim again. Now it is dim after a day. Have i destroyed a diode? Why? What i did wrong? Is it really possible to fry a diode only at 2 seconds without a heatsinking? Aixiz module was fully assembled and i read that A-140 can easily be driven up to 1.5A. Please, tell me, what i was wrong at.
 





eyeballpaul said:
Have i destroyed a diode?
Yes.

Why?
Basically, you fried it!

What i did wrong?
Maybe not using a driver.

Is it really possible to fry a diode only at 2 seconds without a heatsinking?
You did it! Heatsink is for preventing overheat, overcurrent will kill the diode, no matter how well heatsinked they are

Aixiz module was fully assembled and i read that A-140 can easily be driven up to 1.5A. Please, tell me, what i was wrong at.
Click to expand...

Probably your PSU gives a lot more than 1.5A even if it is rated to only 1A.
 
Thats an example of what not to do. First you dont clarify what kind of power supply you are using, but maybe it have some caps in the output that could have send a spike to the diode, or accidentally you could have short the diode even without noticing it... was the power supply connected when you plugged the diode?

You also don't even talk about electrostatic discharges. But seen you were on a hurry I guess you forgot it. An electrostatic discharge could easily blowed your diode. Use always a electrostatic wrist strap handling these devices.

Not all bad news. Wait for your driver, test it with care, and try again the diode. starting at low currents.

Remember, it is better to wait the right moment to do things than cry before its time.
Lasers + hurries equals accidents.

Good luck :)
 
Rafa said:
Probably your PSU gives a lot more than 1.5A even if it is rated to only 1A.
Click to expand...
It measured 1.25A in the circuit.
magonegro said:
was the power supply connected when you plugged the diode?
Click to expand...
Yes, it was turned on, i shorted the circuit by simply sticking wires together for short time.
magonegro said:
An electrostatic discharge could easily blowed your diode.
Click to expand...
Hm, that's an idea, may the reason be in touching the wires with bare hands, while shorting circuit?
 
4.2V not 5V. This may be your problem.

ESD could be a cause but usually a diode will be stone dead not LEDed.

A couple of seconds in the Aixiz shouldn't be too detrimental but at that current it may have been. You mention it was a stabilised PSU. Stabilised how? Constant Current or Constant Voltage? If constant Voltage your diode could have suffered from thermal runaway which would suck more and more current causing degradation and eventual failure. Others may comment in more detail on this.

Bright one second, dim the next, bright again though? Could be runaway as this does happen but there are too many variables to nail a cause I think.

Next time, I would sort yourself out with a proper Current regulated source at less than 5V to start.

Even the 445s are not indestructable! Although there aren't many that have gone poof so congratulations are in order. They're tough beasties to kill!!!

We've all suffered the loss you are feeling so don't let it get you down. Get a driver, another diode and start all over again... ;)

M
:)
 
Kevlar said:
According to IgorT's diode plot here: http://laserpointerforums.com/f65/3x-445nm-ld-piv-plot-53927.html
Click to expand...
No thread (

Morgan said:
Stabilised how? Constant Current or Constant Voltage?
Click to expand...
PSU is not new, from late 80's but I honestly don't know which way it's stabilized. It just says "Stabilized" on it's case:confused:
Morgan said:
Next time, I would sort yourself out with a proper Current regulated source at less than 5V to start.
Click to expand...
Morgan said:
We've all suffered the loss you are feeling so don't let it get you down. Get a driver, another diode and start all over again... ;)
Click to expand...
Thanks for support I'll definitely try:yh:
Could it be a such small voltage overdrive:undecided:
 
If it's a constant 5V driver, then the current depends on the load. Your test load may have only been pulling x amount of current at a constant 5V, but if it was truly feeding the full 5V into the diode then the current through the diode was a lot more.
 
Not sure why the link won't work, I hope IgorT doesn't mind me re-posting his graph here.

Don't know what happened.
28592d1281030853-3x-445nm-ld-piv-plot-445nm-3x-piv-plot.png
 
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If you really want to run diodes off a bench supply, you really need one that has adjustable current limiting. IMHO messing with resistors, etc, is just asking for trouble. Constant current is the safest way. Either with a real LD driver, or a power supply that supports it.

IMG_0008.jpg
 
I paid $35 used for the one I pictured above. It needed some work but nothing major. But the point is they aren't that expensive or uncommon.
 
Using a resistor for test purposes isn't that bad. Practically all bench power supplies are designed as constant voltage sources and have filter capacitor that can empty before the current regulations kicks in. Using a linear voltage to current converter (also known als resistor) is inefficient but does work fine for testing because the voltage regulation on bench psu's is quite good in general.
 
Most likely you diode was killed by transient current.

eyeballpaul said:
The Incandescence lamp i used to reduce the circuit current (stupid way, but had no fitting resistors near at hand and it was late to go buy them, i had a very strong desire to see the blue light). .
Click to expand...
 
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