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why my IR leds get burned out??

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ikalogic

Member
hi,
in less that 2 days i damaged more than 2 IR led taken from old computer mouse, i used to connect them in series with a 1k-ohm resistor.

Is this resistance not enought to prevent to much current to be drained? ?
or Maybe it was only a coincidence ??
or maybe IR leds need special care ??


thanks for any advices. :)
 

panic mode

Well-Known Member
What's voltage you use to power it?
 

ukeee

New Member
To work out how much current flows through the led it is

Vs-Vled/R

so supposing you are running the led from a 5V supply you will have approximately 4mA through the LED with a 1k ohm resistor. Most LED's will work fine with this current you should probably try and track down some datasheets for IR LED's but I don't think they differ much from standard. If you are running at more than 5V the current will increase which could well cause problems. Try using 4k7 resistors.

Are you sure they have burnt out, when LED's do go they usually go with a very quick burst of light whent hey are first connected. Just out of interest what are you trying to do with them?
 

ikalogic

Member
well yes i'm sure there is something wrong with the leds because when i replace the bad leds with other IR leds, every thing works Ok..but how do you expect to se the 'brust of light' as they are "InfraRed leds", i dont' see light at all! :lol:

well it is for kind of experimental alarm system using an IR led an IR sensor .. all taken from old computer mouses! :)

thx for the help, i will try putting 4k7 ohm as i am using 8 Vdc....

thx again
 

ukeee

New Member
Yea sorry you obviously won't be able to see any light. I had a look at some datasheets for IR leds they generally have higher current ratings than standard LEDs typically about 100mA. With a 1K resistor your forward current will be approximately 8mA so this shouldn't damage them. Is it possible that the IR LEDs aren't turning on because they don't have anough forward current, a normal LED would work fine at 7mA but I'm not sure an IR LED would if it is rated at 100mA.
 

ikalogic

Member
about your site...
i still don't see any article .. i would be very happy happy the see an article about techniques to build cool-proffesional-look boxes to encapsulate the PCBs and various projects.. and boxes that coud be easily homemade.

thx a lot and good luck in your site
 

ukeee

New Member
Yea I've been concentrating on sorting the basics of the site out, but most of that has been done now so I'm going to start writing a few articles and put a few projects up that I have on the go. Hopefully once a few projects and articles are up people will start submitting their own projects and articles. It will take a while to get a reasonable user base before the website will really start to work. If you would like an article about housing pcbs you can start one, go to submit an article and simply write a discription of the article you would like to see and then ask other people to contribute to it. It doesn't matter if you don't know how to do it yourelf other members may and they can then contribute to the article. Thats how the website is meant to work. You don't need any special privelidges to submit articles and projects as long as you are logged in as a user.
 

bmcculla

New Member
If you want to see if your IR LED's are working try using a cheap webcam. Low cost webcams leave off the IR filter and so you will be able to detect IR light. Even some inexpensive digital camcorders and still cameras will detect the light.

Brent
 

B-o-b

New Member
IR LED's

Brent is right, U can use 1 of those l'il webcams, or even a security cam will work good. Also, most camcorders will work as well, but there are some of 'em that won't for some reason or another. Try whatever ya got handy... sumth'ns bound to give an indication that yer IR LED's are working.

As to how much current they should draw, well, if specs are not available, I usually assume around 15-20 mA as a rule of thumb. Most standard LED's are in this current range anyway (exept for the tiny led's, which are usually around 5-10 mA).

Cheerz,

Bob
 
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