IR Leds - all broken OR how to test them

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So, I recently got back to an old project and started messing around with IR. For IR, one needs leds. So I dug up my few year old bag of them, static bag, but sadly all of them seemed to have died. That in itself was weird, but I figured that could happen.

 

So, I ordered up some new ones, but quite a few of those are also not working it seems. That was starting to get weird. So, I made up a simple circuit, 30 ohm, 5 volts, 1 Led, and started testing the leds using a camera. Also testing a few red leds to make sure the circuit worked. So far the results have been underwhelming, I can't get much of a reaction out of the leds.

 

I already found out that for SOME of the leds I got, the switched anode/cathode, having the long leg be the cathode, that cleared somethings up, but, I am sceptic, what are the chances that so many leds are broken out of the bag? Is there a way to test IR LEDS, except the camera ones. I now have a test circuit with 30 ohm, the ir and a regular led in circuit. But I am kinda pulling my hairs out over this.

 

Edit: Of course, all this is most likely to my knowledge status, lack of it,  on the subject of electronics, but Google 'testing ir led' and you get a whole bunch of use your camera stuff for remote controls. So that's not helpful. Hope the you guys can be.

Code, justify, code - Pitr Dubovich

Last Edited: Sun. Aug 2, 2015 - 07:47 PM
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Assuming that the LED drops about 1.5V across the anode:cathode junction, there is still 3.5v going through 30 ohms which is about 115 milliAmps of current.  Normally you only want that much current going through an LED when the LED is pulsed using PWM (and a transistor amplifer/buffer). 

 

Maybe you have been burning out the LEDs with the test.   Use a 330 or 470 ohm resistor if the LED is constantly on.
 

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Sounds like you might be giving them too much current. Some are rated at like 150mA, but that's because you pulse them at 10% duty cycle.

 

A digital camera or cellphone can see the IR. It looks purple or violet on the screen. Smartphones are very handy things.

 

Curiously: This editor does not work quite right in Microsoft's new "Edge" browser. Somehow, I'm not surprised

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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Still, I find it hard to believe that all my IR's are burned out. I also tried measuring them with the multimeter, I don't know what I am doing wrong. 

Use a 330 ohm resistor when they are constantly on? 

 

I now have

 

5v --------> 60 Ohm ---> Ir Led ---> Normal Led ----> Grnd

 

If the normal led lights up, the IR led is working, I figure.

 

Code, justify, code - Pitr Dubovich

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How are you trying to detect if the IR is working?    IR LEDs are usually pulsed at 38KHz when they are ON.   Your IR detector circuit may be expecting the IR to be in 38KHz pulses before it indicates that it is 'seeing' an active IR LED.

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If the IR led is working, ie, conducting, then when the IR Led is present, the regular led will turn on. I am not trying to detect if it's transmitting, just if it's 'on' or off. I look at it via a camera, some leds are working, some are not.

Code, justify, code - Pitr Dubovich

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330 ohms ought to be fine.

 

So, what's with these LEDs? Hmm...

 

Often a multimeter on an ohms scale won't put out enough volts to turn the led on and get any current through. If your meter has a "diode" setting, try that. It puts a higher voltage through a resistor. Otherwise, use a resistor in series with your meter and the led and see if you can measure any current flowing.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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Okay, I build this circuit, with a transistor and 1K ohm resistor to test the led. My logic is, if the led is ok, it will drive the transistor and the regular led will light up, that make sense? 

 

Code, justify, code - Pitr Dubovich

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Semiconductors normally fail short circuit. Why such a circuit? Just a resistor and a multimeter would suffice. Will the red led like being fed via a 60 Ohm resistor?

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I don't understand, why is that a short circuit?

 

And how would I measure with a multimeter and resistor, just measure the voltage?

Code, justify, code - Pitr Dubovich

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I don't understand, why is that a short circuit?

I believe he is pointing out the fact that since semiconductors typically act as 'short circuits' when they fail your circuit will not be able to determine if the IR LED is good or if it has failed.  In either case the RED LED will be ON.

 

Don

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Ah, if the led itself is shortcircuited, it might light the circuit, so if my checking led is on, the IR might still be bad. However, if the checking light is OFF the Ir certainly is bad.

Code, justify, code - Pitr Dubovich

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There is still about 60+ milliAmps (3.5V/60 ohms) going through the red LED.  That's enough to burn it out in a blaze of glory.  There are about 2.8 mA through the InfraRed LED ( 5vcc - (1.5v LED drop + 0.7 base/emitter drop).

 

Get an old hand held remote that still turn a television set.    Open it up and remove the IR LED.  Use alligator clips and wires to the former LED's leads to test each of the questionable LEDs.  If they turn on your TV when you press the power on/off button on the remote, then the IR LED is good.

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You can usually see IR with/via your phones camera , test on a working tv remote. And  then the IR diode in question.

 

/Bingo

 

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The handheld remote thing seems a nice twist. May try that one if I find a remote.

 

I am fully aware of the IR being visible on camera trick, but I still can't figure out WHY all those leds all seem to have failed, while all the new ones are working. Are IR leds especially fragile, do they break easy, are they susceptible to static in another way then regular leds?

 

I've only once damaged a regular LED once in many years, but IR leds seem to be dying by the handfull.

Code, justify, code - Pitr Dubovich

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Hi Eloque.

 

Sorry to hear of your current troubles... (maybe a pun).

 

Can you give us a link to the datasheet for the ones that are dying?

 

Cheers,

 

Ross

 

Ross McKenzie ValuSoft Melbourne Australia

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Hi Ross, currently about 15 or so of them died. All of them pretty bog standard. I am resisting the urge to give up on them and switch to a new supply.

 

  • Diode Case Style: T-1 (3mm)
  • Fall Time tf: 12ns
  • Forward Current If(AV): 100mA
  • Forward Voltage VF Max: 1.5V
  • MSL: -
  • Operating Temperature Max: 100°C
  • Operating Temperature Min: -40°C
  • Packaging: Each
  • Rise Time: 12ns
  • SVHC: No SVHC (15-Jun-2015)
  • Viewing Angle: 13°

 

http://www.farnell.com/datasheet...

 

I am really starting to think that I stored them wrong or something, but can't quite wrap my head around that as I don't recall leds being that fragile. Hell, one led I liberated from a broken remote, soldered new legs on and that one works just fine, I don't even HAVE a datasheet for that one.

Code, justify, code - Pitr Dubovich

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Well providing you do not exceed the 100mA maximum current, I don't see how you could be destroying these. With a 5 volt supply and 60 ohms series resistor (do I remember that value correctly from a post by you above?), you can only reach 58mA.... so SAFE. But the reverse voltage of 5 volts would destroy them. Is it possible that you connected any around the wrong way?

 

Ross McKenzie ValuSoft Melbourne Australia

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Well, it would be nice to know what happened to all of these before you get and destroy a bunch more. I've had LED sitting in plastic drawers that worked fine 20 years or more later.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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valusoft wrote:

Well providing you do not exceed the 100mA maximum current, I don't see how you could be destroying these. With a 5 volt supply and 60 ohms series resistor (do I remember that value correctly from a post by you above?), you can only reach 58mA.... so SAFE. But the reverse voltage of 5 volts would destroy them. Is it possible that you connected any around the wrong way?

 

Yeah, I could've. But, the new ones I already hooked up wrong a few times, remember, they have the Anode/Cathode switch, long leg being ground for some reason, but after reversing those back to proper again, they worked.

 

I'd really like to know what happend to those. I know it's only a few cents a led, but, really, they used to be more robust.

Code, justify, code - Pitr Dubovich

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Reversed lead assignments is lunacy. The manufacturer should be shot!

 

Reduce your voltage to say 3 volts and then you should be well within the maximum reverse breakdown voltage.

 

Ross McKenzie ValuSoft Melbourne Australia

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Sounds a bit like testing fuses!

Leds do have a low reverse voltage rating - they seem to degrade over time when the voltage is reversed - it doesn't seem to be sudden death. There's probably a good explanation for this, but my semiconductor physics is very rudimentry.

Last Edited: Tue. Aug 4, 2015 - 01:36 PM
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Yeah, I could've. But, the new ones I already hooked up wrong a few times, remember, they have the Anode/Cathode switch, long leg being ground for some reason, but after reversing those back to proper again, they worked.

If you aren't sure which lead is which then connect two of the LEDs in parallel (long lead to short lead in each case).  The correctly biased one will light up and it's forward voltage drop will protect the reversed biased one.

 

Don

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Kartman wrote:

Sounds a bit like testing fuses!

Leds do have a low reverse voltage rating - they seem to degrade over time when the voltage is reversed - it doesn't seem to be sudden death. There's probably a good explanation for this, but my semiconductor physics is very rudimentry.

 

Probably because they were designed to be LEDs, not rectifiers or zeners, so they didn't worry much about the reverse voltage.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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5V,  30ohm...for a std. LED with a fwd. voltage around 1.2V, means over 120mA.  That's well into the frying zone to me.

 

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