Odd driver problem

[matt09]

I've just made up the standard regulator circuit with the lm317t IC but for some reason after checking and double checking, the voltage remains the same coming out as going into the circuit.
I'm a pretty good solderer so i don't think i overheated the IC when soldering it
Does anyone have any instant thoughts?

 

[Gazoo]

You need to put a load on it...it doesn't have any current to regulate without a load..

 

[matt09]

Dam I feel stupid now.. of course..
I have the LD running now at 245ma and it looks quite dim and certainly can't burn anything but it does get warm. I haven't let it go over this current level so I don't think it's damaged unless something happened putting it in the case mount :s

 

[Gazoo]

No, don't feel stupid...we have all gone through learning curves and we are all still learning..

Running at 245ma's it should be lasing, it sounds like it is now an LED.. :'(

Is this a GB diode...where did you get it?

Did you hook the meter up before or after you applied power? If you hooked it up after you applied power, you sent a full voltage spike to the diode. This too can kill it.

To avoid this, put a 1 ohm resistor in series with the laser diode, and set your meter to measure voltage in microvolts. Measure the voltage across the resistor and this will give you the current.

Save the diode for further testing, it will provide a good load as long as it is red. And don't feel bad...I have sent at least 15 diodes to the graveyard.

 

[matt09]

Yeah, its a GB, I can't understand how it could have blown already although I have been hooking it up when the circuit is active giving it a 9 volt spike :'(
Further more I've been using a cheap DC power adapter as the power source.
I'm still not 100% certain it is blown though, is there any way to tell though any readings such as current etc, it does still look quite bright focussed and it was in a well lit room.

 

[Gazoo]

Well it might be lasing if the dot is real bright. Turn the lights off. If you see a beam it is lasing. Look towards the beam (not directly at it!) and away from the beam. If it is lasing the beam will be very visible.

 

[Benm]

You could have been unlucky and gave it a jolt of static when working on the diode. Happened to me last week too... it's getting colder here and on dry days it's becoming a bit of a problem sometimes. Ofcourse i could have taken ESD precautions, but didnt realise it was jolt-from-the-car season already

 

[LarryQ]

Ofcourse i could have taken ESD precautions, but didnt realise it was jolt-from-the-car season already

HAHAHAH

Man Do I hear you.....in the winter I swear my truck is trying to electrocute me!!!!

May be time to give up harvesting for the winter!

LarryQ

 

[Hemlock_Mike]

Matt --

Did you have the capacitor directly across the LD wires , right at the base? A good cap will absorb the spike.

Mike

 

[IgorT]

Yeah, its a GB, I can't understand how it could have blown already although I have been hooking it up when the circuit is active giving it a 9 volt spike  :'(

Your above sentence answers your question, about how you killed it.

You should never connect the LD to a powered circuit. The circuit itself was charged to 9V and so was the capacitor, meant to protect your LD. Once you then connected the LD, all the capacitors capacity discharged into the LD, along with some of the power from the circuit itself...

Before i attach the LD i not only make sure the circuit is off, but i also short the capacitor first! This way it fully discharges, just in case it had a load.

Then i solder the LD to it, and never again remove it from the cap. If i have to measure the current i measure it BEFORE the cap..


Before this i also killed 2 LDs and was very sad.. Now that i'm more carefull, my third one is still working nicely and can do burning if focused correctly..


One more thing.. You can't tell if the LD is still good just by the current.. With the two (actually four, but those were not DVD) LDs i killed, they continued consuming A LOT of current even after COD. Only after i tried driving them even harder (by raising the voltage) did they die completely..


I'm afraid you'll have to get another LD. You'll need spares in any case.

Also, test your circuit on an array of LEDs before trying a LD with it, and measure all that is going on, then power the circuit down, short the capacitor (a couple of times, just to make sure) and only then solder the LD there.. Start with a pot at it's maximum setting (lowest current) and then gradually work up from there, while measuring the current.

Good luck!

 

[matt09]

Thanks for all the replys guys, sorry to turn it into yet another 'omg my diode broke' thread.
Benm, I did use an antistatic wrist strap when handling the diode and soldering so hopefully that wasn't the case. I had two wires on the LD an nothing more, the regulator circuit was seperate meaning i was discharging 9 volts into the diode rather than protecting it.
I typed that before reading your post Igort, thanks for confirming that.
As for the rest, I have done already, I've done quite a bit of reading on these forums

Edit: on the now deemed blown LD, the regulator is getting very hot even though it is only putting out 250ma, I have read that it should stay at room temperature even after long operation does anyone know the cause of this. The only thing I can think of is that blown LD's have a high internal resistance?, combined with the already decreasing resistance as it heats up

 

[IgorT]

I typed that before reading your post Igort, thanks for confirming that.

I learned the importance of discharging capacitors before handling them, the hard way.. And i'm not talking about these small tiny capacitors.. I'm talking about huge capacitor arrays charged to 400V, with enough power in them to vaporize (well kill actually) 10 people in a row..

There i had to make a small cap discharge thingy with huge high wattage resistors in it, to short the cap without killing it.. Otherwise, those were capable of putting out 100A or more in one big jolt..

And many of those jolts went through my body, but luckily never from an entire array, only from a single cap. But it was still enough to drop me to the ground yelling..



Here there is hardly any power in the capacitor, but the same thing still happens, only on a much smaller scale.

LDs are so sensitive, it's better to make sure.. Just put a screwdriver across the capacitors leads, to make a short (with the circuit off first, of course).

Now that i'm more carefull, my LDs stopped dying.. And so will yours.


Good luck!

 

[Greyfox]

Edit: on the now deemed blown LD, the regulator is getting very hot even though it is only putting out 250ma, I have read that it should stay at room temperature even after long operation does anyone know the cause of this. The only thing I can think of is that blown LD's have a high internal resistance?, combined with the already decreasing resistance as it heats up

You said you're using a cheap wall-wart to power your regulator? Those are notorious. They're unregulated, so they put out far more than the indicated voltage if you're not sucking off the rated current. I've seen the 9V ones regularly pushing 15V on low loads. If that's all you have for power, I strongly recommend you get a heatsink and attach it to the LM317 with thermal paste. Just be careful, the LM317's tab is hot. It is tied to the output line.

 

[chimo]

I'm not sure how it was worded regarding the LM317 not getting hot, but that is certainly not true for all situations. The amount of power dissipated in the 317 is a function of the input and output voltages and the current. Let's take your example:

A GB LD running at 250mA is going to have a Vf of around 2.85V. If it is running in regulation, the sense resistor will drop 1.5V too.

So, the load voltage the LM317 sees is about 4.35V. (2.85+1.5)
You are feeding it about 9V.

Therefore the LM317 is dropping about 4.65V from the Vin pin to the Vout pin. The current, as mentioned, was 0.25A.

The LM317 is dissipating:
4.65V x 0.25A = 1.16 Watts

That's enough to make the LM317 nice and toasty warm.

You may also want to verify the power adapter you are using really puts out 9V. Measure with the circuit energized and LD(LED ) connected. You may be surprised how different the no-load and lightly loaded voltages differ from the nameplate figures of those wall-warts.

Edit: on the now deemed blown LD, the regulator is getting very hot even though it is only putting out 250ma, I have read that it should stay at room temperature even after long operation does anyone know the cause of this. The only thing I can think of is that blown LD's have a high internal resistance?, combined with the already decreasing resistance as it heats up

 

[IgorT]

You said you're using a cheap wall-wart to power your regulator? Those are notorious. They're unregulated, so they put out far more than the indicated voltage if you're not sucking off the rated current. I've seen the 9V ones regularly pushing 15V on low loads. If that's all you have for power, I strongly recommend you get a heatsink and attach it to the LM317 with thermal paste. Just be careful, the LM317's tab is hot. It is tied to the output line.

That's true.. The stronger they are, the higher voltage they put out..

For example the ones rated for 1A, have an open circuit voltage over 16V when set to 9V. Only after you connect a load of 1A does the voltage drop to approx 9V..

Also, all the voltage spikes from the wireing in your house go straight through..


matt09: When you said you had 9V in your circuit, did you actually measure this voltage, or is 9V just what you set your cheap DC adaptor to?

One thing you can do, when your unregulated DC adaptor is putting out too much voltage, is simply to set it to a lower voltage.. You can usually set it to 6V and still get 9V or more, when not using up all the current it can supply.. But it's much better to simply use a LM7805 before the LM317. This way you have a stable voltage AND current, no matter what you put in (within limits of course)...

In any case, you need to use a multimeter to check everything BEFORE connecting your LD to it, just to make sure, what's really going on...

 

[matt09]

Thanks for all your replys, it turns out I had blown the first LD, but I now have the 2nd working fine in an Aixiz module, apart from tha fact it won't burn anything even though focussed within a milimeter or two :S

Regarding the PSU, I was only using the adapter to test it and wasn't planning on using it as a permenant power source. I was running at about 12v into the regulator and yes, I believe it is a cheapo unregulated one. I forgot about the voltage drop etc and was thinking it would only be pushing 250ma x 3v but of course this is only the output so thanks for setting that straight.
I'm using the 12v rail of from my pc for testing now hehe