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How did i Kill my Diode

justinjja

justinjja

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Mar 2, 2011
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Its an LPC-826
I put it in an axiz module,
got 2 D-cell alkiline cells in series (~200mOhm internal resistance)
in series with my multimeter (another 100mOhms)
in series with my diode.
was using a 650 G2

Current reading was just over 300mA


It was not in a heat sink, just the axiz module, but i only turned it on for a couple seconds before turning it off, and the axiz did not get warm.

I turned it on and off a few times, then it got really dim,
but my meter still read 300mA

Not a big problem, i bought 2 diodes for this very reason,
I just dont want to kill the other one...
 
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NEVER direct drive a diode. You can't rely on the internal resistance of batteries to set the current, even super short duration spikes can kill a diode.

Honestly if you're going to spend money on a G2 lens, why skimp on a good driver? A LM317 driver circuit is maybe $6.
 
well i was measuring the current to be about 1/2 of what the diode should be able to handle.

it seems strange that that would kill it?
 
justinjja said:
well i was measuring the current to be about 1/2 of what the diode should be able to handle.

it seems strange that that would kill it?
Click to expand...

Unfortunately that's not how it really goes down. Like Sigurthr said, you need a driver. No two ways about it. Laser diodes heat up which makes them try to get more current supplied to them. So eventually that set up would fail. But seriously, why spend all the money and not invest in a quality driver?
 
Fretwrecker94 said:
Unfortunately that's not how it really goes down. Like Sigurthr said, you need a driver. No two ways about it. Laser diodes heat up which makes them try to get more current supplied to them. So eventually that set up would fail. But seriously, why spend all the money and not invest in a quality driver?
Click to expand...

Ive built a 635 laser that ran straight off of 2 D cells and it has ran fine for hundereds of power cycles and hours of use.

but anyway that would not be my final setup, i plan to adventually build a driver, however i am convinced that somthing else killed this diode, and i dont want it to happen to my other diode.

I know that a ld will pass more current as it heats up, but i didnt allow it to heat up, and it failed while pulling 300mA.
 
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justinjja said:
Ive built a 635 laser that ran straight off of 2 D cells and it has ran fine for hundereds of power cycles and hours of use.

but anyway that would not be my final setup, i plan to adventually build a driver, however i am convinced that somthing else killed this diode, and i dont want it to happen to my other diode.

I know that a ld will pass more current as it heats up, but i didnt allow it to heat up, and it failed while pulling 300mA.
Click to expand...


I'm assuming that 635 diode has survived because they can handle a lot of current. But LPC-826's aren't as tough. Power spikes can kill them pretty quickly which is probably what happened.
 
justinjja said:
can you get power spikes when direct driving with batteries?
Click to expand...

Absolutely! Aside from limiting the current, that's what a driver protects against. It's like when you turn something on even though it has dead batteries, it turns on for a split second but then can't power it anymore. But this happens with fresh batteries as well, they give off too much voltage for the diode and it gets fried.
 
Interesting,
never the less it was running at 300mAh so im still not convinced that current is what killed it.
 
justinjja said:
Interesting,
never the less it was running at 300mAh so im still not convinced that current is what killed it.
Click to expand...

Voltage and current are different from each other. Imagine Voltage as a truck. The current is how hard the truck hits you. The higher the current, the higher the "hit". So a truck hitting you at 1 mph moves you a lot less than a truck hitting you at 100mph. Likewise 3V @ 30mA drives a diode far less than 3V @ 600mA

A power spike is when more voltage than a cell is rated for passes but stabilizes very quickly. the excess voltage is higher than the diode can handle. The tolerance on diodes is not enough to save it from this. Diodes are VERY sensitive.

Also mAh is milliamp hours. Aka it can last at 300ma being drained for 1 hour. If you ran something at 600mA, itd only last 30 minutes.

I think you meant to say 300mA. But current fluctuates when direct driving. Nothing is "perfect" in electronics. If this were true, nobody would need drivers.
 
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The current is definitely what killed it. Fresh D cell batteries are able to provide over 12 AMPS. Your DMM is not fast enough to capture the current spike when you turn it on. You need an oscilloscope to see that properly.

If you are going to direct drive a laser diode, at the VERY least, use a resistor!
 
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Things said:
The current is definitely what killed it. Fresh D cell batteries are able to provide over 12 AMPS. Your DMM is not fast enough to capture the current spike when you turn it on. You need an oscilloscope to see that properly.

If you are going to direct drive a laser diode, at the VERY least, use a resistor!
Click to expand...

Thats just it, it didnt die when i first turned it on, it died when it had been on for a second or 2, and the multi meter was clearly showing ~300mA

I guess it is possible that there was a spike that dammaged the diode, but didn't completely kill it, then durning the following seconds the diode died.
 
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Of course, the initial spike damaged the cavity mirrors, which burnt themselves out during those few seconds.
 
the fail is strong in this thread .............

look man you cant direct drive a diode. diodes are current devices so they are like greedy a$$holes they never get enough current. so you have to limit the current they get. especially if you are using D batteries that can give multiple amps to a diode that you should drive in the 400-500ma range.
 
have to disagree with you, ultimatley you can build direct drive lasers, given the right circumstances
as i mentioned earlier I have done it before, and so have others,
just not with these specific circumstances.
 
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justinjja said:
have to disagree with you, ultimatley you can build direct drive lasers.
Click to expand...

Yes, and no. They dont always work. As good practice its always better to use a driver so you dont run the risks of frying the diode, and red diodes are the only diodes I've seen that can work with direct connection.

But, just because one of yours worked doesnt mean it will work all the time.
 
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