Testing at High Currents in Motion

[Meatball]

I don't know who this is, but they are testing one of these diodes at 1.5A!

He claims that his projector was running the diodes at about 1.4A at lower duty cycle in economy mode. He claims that AVERAGE power in the projector was about 800mw per diode, and then claims to say that the ON period of the cycle has them run at 2.25W.

I'm going to be checking back there to see what happens. He is running the thing at 1.5A until it dies.

445nm laser diode

EDIT: I found that he can be contacted at 4hv.org. Username: ...

What do you guys think? Time to turn up the power?

 

[oic0]

A guy on here tested one to see what it could handle and I believe he burned one out around 1.8? or was it 2.2... would have to find the post. Had some good info. Was the heuristicscience screen name or something like that.

 

[ossumguywill]

Yeah, he said that the SAFE max power level was 1.84 watts, by taking the COD wattage and multiplying it by .707.

 

[pullbangdead]

Yeah, he said that the SAFE max power level was 1.84 watts, by taking the COD wattage and multiplying it by .707.

Which I don't believe is a valid method.

 

[ossumguywill]

Why not? He seemed pretty sure you multiply the death power by the RMS ratio of a sine wave.

 

[Meatball]

He said that it was over 2W before it popped. I don't know where that it on the current scale.

What does the RMS sine wave ratio have to do with the max current allowed before COD? Any documentation on this?

 

[pullbangdead]

I don't quite get exactly what it was he was trying to say, but my interpretation is that he's applying a statistical method to a sample size of 1...a sample size which is not statistically significant, to put it mildly.

 

[ossumguywill]

He said that it was over 2W before it popped. I don't know where that it on the current scale.

What does the RMS sine wave ratio have to do with the max current allowed before COD? Any documentation on this?

No idea... but heuursciences or whatever (I can't remember lol) said it was an appropriate method.

 

[Meatball]

Hmm.. I just know that EVERY diode is different.

And if this is just another GaN diode, then does that mean they will act similarly as 405s when we ramp up the current?

I don't know about Chris sometimes... I don't know were he gets some of his stuff.

 

[pullbangdead]

And if this is just another GaN diode, then does that mean they will act similarly as 405s when we ramp up the current?

There will be slight differences because of multi- vs single-mode, but in essence, most all the laser diodes we see here run on the same physics. The L-I-V curves will look very similar.

 

[heruursciences]

We need some other people to test one to destruction for the cause, I am sure the .707 works for shorter wave IR and red diodes, but of the new nitride based blue ones I am still a bit unsure.

I do know for sure they are run at about 800mw average power output in the lowest setting of the projector, meaning they are being driven over a watt of power during the ON time on the lowest brightness setting.

FWIW The graph does appear that there are two types of diodes though

 

[Meatball]

Ok, that's good to know. We shouldn't see much of a knee, or kink once more should we?

I am convinced that setting one to 1.5A should yield a reasonable lifetime if a duty cycle is observed.

I have three diodes to work with, one will be set at least that high.

I'll ask Chris about how long it took at what current to pop one.

EDIT: Oh hey Chris! So how did it happen for you?

So the RMS ratio was good for reds and IRs, but not necessarily GaNs.. Ok good to know.

How did you come across "Average" power? The guy who wrote the linked web page claim it was 2.25W!

 

[heruursciences]

The beam in the projector is pulsed. The .707 thing was a discovery from years of playing with laser diodes .707 of the COD value gives the absolute theoretical operating power that can be safely sustained.

COD is the minimum value of drive current that causes permanent damage to the laser. The output immediately drops at a given current level signaling immediate catastrophic failure. In short a part of the LD cavity reflector melts.

 

[ossumguywill]

The fact that it shares the sine wave RMS number is very interesting to me. Any idea why?

 

[Spoz]

The fact that it shares the sine wave RMS number is very interesting to me. Any idea why?

It's completely arbitrary. It corresponds to half power (The square root of 1/2). This number comes up frequently because it is easier to decide on a "safety factor" to use in cases where there is no real correct answer for the "safe" value when given a "failure" value. Engineers started using sqrt 1/2 and it stuck.

 

[daguin]

bump

Peace,
dave