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FrozenGate by Avery

Strange voltage problem with DDL's Driver

C

Cxrazy

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Aug 15, 2007
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Hey guys,

I just assembled DDL's driver, and I have seen blu-ray light goodness!!!!

I only have 1 problem, and it is a bit major.

While measuring the voltage across the diode, i turn my pot slowly until it begins to lase, I get it to about 4.3v, where the brightness looks about right, and its 45ma. then my voltage slowly drops, eventually dimming the laser to nothing. I can turn my pot back down to where the laser doesn't lase (~3.1v) then turn it up and it will repeat.

It seems like any voltage about 3.7v will eventually just drop down below the lasing threshold of th diode.

I placed a 400uF cap across the power input to the circuit, and this helped, but it still drops.

I've tried this on 2 different power supplies. :'(


HELP ME!!! >:(
 





What are you using for your power source? Is it at least 3v above max voltage required by the LD?

Regards rog8811

*Edit Your power supply isn't constant current is it?
 
It is a 12v computer power supply. Also a 12v-6v switching car battery charger majigger.

perhaps I have a faulty LM317?
 
it could possibly be constant current. its rated 1amp.

Would this adversely effect it?

I'll probably need to get some batteries to test it with. What 2 batts do people use with Blurays again? I'll go look...
 
2 X RCR123 rechargable....7.2v
or 1 X PP3..... 9.0v

Regards rog8811
 
1. Power supply my not be stable with low amount of current your using.
2. The vary-resisstor is pushed with current and heats with the LM317, it may be flaking out.
3. If your wired connections are loose your LASER is doomed.

DGM
 
Driving the 317 with 12 volts may result in the thermal protection of the 317 kicking in...it does with my reds. And I have small heat sinks attached to them. So with 12 volts the 317 needs some good heatsinking. At 9 volts the regulators are fine. They do get hot but they don't shut down. When thermal protection kicks in the power drop is gradual, so I believe this may be your problem.

I recommend you try a standard 9 volt alkaline transistor radio battery and see what happens. Make sure you have your pot turned to the highest resistance, then adjust as necessary.
 
with 12v input, putting out ~4v at 30ma its gonna overheat?

My LM317 just broke off my PC board as I was fiddling with adding a heatsink.

I'm about to shoot someone.
 
I wouldn't think the LM317 would overheat dissipating just .16W. maybe a loose connection? But the symptoms do sound a lot like the thremal protection kicking in...how hot did the regulator get?
 
I've tried it with a 9v DC 500ma transformer, a 9v AC 200ma transformer I ran thru a bridge, a 12v computer power supply, a 12v car battery charger, and a self built 12v DC transformer, many 9V batteries, and 3xCR123's.

All eventually drop off. I have also rebuilt the circuit. Much neater, smaller, and i can verify that it is correctly wired.

Does anyone else have a suggestion!?
 
Cx, let me tell you... you have quite the problem. :-? :-/

Although, allow me to ask what no one else asked...

While measuring the voltage across the diode, i turn my pot slowly until it begins to lase, I get it to about 4.3v, where the brightness looks about right, and its 45ma. then my voltage slowly drops, eventually dimming the laser to nothing. I can turn my pot back down to where the laser doesn't lase (~3.1v) then turn it up and it will repeat.
Click to expand...

This says that you are running it in voltage control, not current control... How are you wiring the LM317? ::)

On the other hand... I personally have never seen any laser do this king of thing unless it is all a supply problem. The thing about the laser diode is that it works like an electrical short with a specific voltage drop associated with it. Any diode (if it can handle it) will sink as much current as the circuitry could provide. If the current is dropping, it's not a diode problem.

Here are the first things to check:
  • What pot are you using? What is it rated at (voltage, current, power)?
  • What size LM317 are you using?
  • Which driver are you talking about? The diode driver (9V), or the regulated power supply (12V)?
  • Have you tested a transistor LD simulator? an LED by itself without a resistor (or an array of them)?
  • Grab a set of 1N400X silicon diodes from ratshaq ($0.99) and set about 7 of them in series and see what you get.
  • How are you measuring the current/voltage? (Use a 1-Ohm resistor and measure the voltage across that instead of any other method as this is more a more accurate and a safer method that has minimal effect on the circuit/LD).
  • Post video/pictures please :)

Hope I can be of help... ;) (Sorry for the late reply)

--DDL
 
Thanks for the reply DDL! Heres the answers to all of the above questions:

  • I am using the 100ohm pot that you sent me with the kit.
  • I am using the NTE956, an exact copy of the LM317, but by a different company. its the same size as the LM317 you sent me, and I had the same problem with that as well.
  • I have tested an LED by its self, and ran the circuit at a 40mA with no problems
  • I'll have to test out the diodes in series.
  • I am measuring voltage/current across the 1ohm resistor, so I believe my measurements are accurate.

    I will upload a video of its behavior later today.
 
Cxrazy said:
do I have the regulator wired wrong if both voltage and current increase with eachother? say 3.2v @ 25ma and turn the pot I get 4.1v @ 40ma.

should the voltage be constant and the current be the only thing to change? because that could easily fix my problem.
Click to expand...

No because it is impossible to increase one without increasing the other and visa versa. It is very rare for a 317 to go bad. Something is very strange here. Are you sure you have it wired up correctly and nothing is shorted anywhere?
 
Every time someone says they're using the NTE956 to drive a laser diode, it is because they're having trouble with it. I'd say stick with the LM317 as we know that works. ;)
 
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