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Redrivering a DX green

tomcat

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project: re driver my dx green with my own creation
its a truedx100 (newwish)

but i need to know the approximate current to put into that 808 diode and the driver board from the dx is shot so no readings

i am looking to get 40-50mw out of this green to stop mode hopping issues

the driver must be quite small and run from 3xAA (which also run a mini spirograph)

50mw green beats 3mw red :)
 

Benm

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I've tried with a DX20, optimum current is around 300 mA in that. Also, i noticed that it actually got dimmer when putting more current in than that. I guess you should just hook it up to a variable driver and see what happens ;)
 

tomcat

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so around 1A should do me :) i will use a LM317 High Current driver (more dropout though)
 

IgorT

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No way! 1A would most likely kill it instantly.

I measured two DX200s and they both drew from 550 - 730mA, depending on the batteries.

The DX lasers from TrueDX50 up all have the same pump diode, which is a 0.5W 808nm 9mm diode.
The power differences mostly come from the crystals and the alignment.

If you want less power to prevent modehopping, reducing the current might help, but it could make things worse.

If you're gonna change the alignment, it could actually resolve the modehopping and even make it more powerfull, but it's a very complicated and painstaking process, due to the way it is built. I wouldn't recommend trying, unless you have lots of experience and even more patience.


What kind of mode hopping problems do you have? How long does it take for the beam to split?

My first one would split in two beams instantly, the second would work up to a minute, but would split into four of five beams. With the second one, i could have resolved the modehopping with a slightly reduced current and better heatsinking, but it had abrupt brightness changes during warmup, so i returned it.

Depending on how yours behaves, there are different solutions for the problem.


But if you want to drive it from 3 AA cells, you would need a very low dropout current regulator. The easiest way would be to use a 317 circuit with two Li-Pos. A 317 won't work from 3 AA cells, unless you're talking about 14500 Li-Pos..

Another possibility, that would work from 3 AA cells is the AMC7135. But there you're stuck with 350mA, which would most likely be too little, and 700mA (with two AMCs), which would be too much, and you'd have to waste some current through a bypass resistor.

A safe current would probably be up to 600mA, but 500 would be safer, since i heard about one dying at 600..
 

Benm

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I measured two DX200s and they both drew from 550 - 730mA, depending on the batteries.
Sounds right for a half-watt pump diode. My 300 mA measurement is from a DX20, which will probably have a 200/250 mW pump. Since you measured 730 on batteries, i seriously doubt 600 mA could kill it rapidly, though it could reduce life obviously.

I'd probably start with 500 mA or so and then see if increasing current to 550/600/650 mA actually makes much of a difference in light output.
 

IgorT

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Well, mine could take these currents easily, but on a DX200 thread, someone said his died at 600.

Otherwise i noticed there are certain currents, where the laser remains stable for longer, or doesn't mode hop at all. Probably because it doesn't heat up that much. The heatsinking in these is horrible. The module doesn't even touch the body properly, so when it's warm outside, it must be very hot inside.

Abrupt current changes can also cause mode hopping, or at least it's related, so constant current alone could help.

When i powered my second DX200 from a 3V CR2 the current was 730mA, but when it would split into four or five beams, the current would suddenly drop to 650mA for some reason.

I powered it on a couple times, and everytime i noticed the same thing. 730mA - one beam, a few seconds later suddenly four beams and a sudden drop to 650mA.

I don't understand what caused this current drop, as later, in some attempts the same battery (not recharged) would continue supplying 730mA even after it split into four beams. But in most cases there would be that weird drop at the same moment as the beam would split.
 

Benm

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It's and odd problem, mode hopping isnt caused by the pump diode directly, but there seems to be a relation between current draw and the problem. It could be that the driver is plain unstable, and somehow the lower current also causes a shift in pump diode temperature and hence wavelength.

With some bad luck this could cause a wavelength mismatch with the solid state laser and thereby cause mode hopping. I guess the only thing to do is find a stable current and hope it works out to be valid over a usable (ambient) temperature range.
 

jmgallego

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IgorT said:
...I measured two DX200s and they both drew from 550 - 730mA, depending on the batteries...
Beginner's question ;) how did you measured the current on these lasers?

Thanks...
 

jmgallego

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IgorT said:
When i powered my second DX200 from a 3V CR2 the current was 730mA, but when it would split into four or five beams, the current would suddenly drop to 650mA for some reason.
Could it be from overheating not so much from the current driving it?
 

IgorT

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Yeah, these often mode hop when they get hot. Especially, since the manufacturer uses air as a heatsink for some reason.

That is why i was so surprised, when the current would drop almost every time at the exact same moment as it would split into four beams. I finally have two "good" DX200s now so i'll use them to build a better laser in a more massive body and with a real constant current driver.

Once i replace the "air heatsink" with a metal one, the power should remain much more stable, and less heat will also mean a lower likelyhood of mode hopping.
 

jmgallego

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IgorT said:
Yeah, these often mode hop when they get hot. Especially, since the manufacturer uses air as a heatsink for some reason.

That is why i was so surprised, when the current would drop almost every time at the exact same moment as it would split into four beams. I finally have two "good" DX200s now so i'll use them to build a better laser in a more massive body and with a real constant current driver.

Once i replace the "air heatsink" with a metal one, the power should remain much more stable, and less heat will also mean a lower likelyhood of mode hopping.
I placed an order for the newer version.  As soon as I get it I will check it out and let you know how the behave (schedule ship date 5/17).   Hopefully these new one do have a better heat exchange.
 

jamilm9

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this is off topic but if i bring the cap off the front of a new wish laser can i put it back on.
 

rog8811

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can i put it back on.
Only if you can get it off without kn*ck*ring it in the first place!
They are sods to get off but should push back on with no problems.

Regards rog8811
 

jamilm9

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so if it keeps its shape i should be able to put it on and bring it off easily.
 




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