All About Circuits Forum How to find out the voltage of a IR led ?
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#1
11-18-2008, 02:21 PM
 marcolisi Junior Member Join Date: Nov 2008 Posts: 15
How to find out the voltage of a IR led ?

Hello guys,
I have an old sony nightshot camcorder.

I am planning to get out of it the IR leds that are inside to use for another sony camcorder as external add-on IR light source.

The problem is that I do not know the voltage of the led.
It is an IR led (two leds) , and I do not kow what is the maximum amout of Voltage that they can get without blow up.

Is there any way to find it out ?
Thank you
#2
11-18-2008, 04:06 PM
 mik3 Senior Member Join Date: Feb 2008 Location: Cyprus, but now in UK (GMT+0) Posts: 4,846 Blog Entries: 9

Check on the pcb, sometimes values of the components or part number are written on pcbs.
#3
11-18-2008, 04:18 PM
 SgtWookie Expert Member Join Date: Jul 2007 Location: In the vast midwest of the USA; CST Posts: 22,030

It's more like what current will they take without blowing up.

20mA is likely safe. IR LEDs usually have a pretty low forward voltage.

To make an easy constant current 20mA regulator, connect a 62 Ohm resistor between the OUT and ADJ terminal of an LM317. Connect +6v to +7.5v to the IN terminal. Take the current from the ADJ terminal.

The LM317 will drop about 3v across itself. Most LEDs have a PIV (peak reverse voltage) around 5v above which they will be destroyed, this is why I suggested a maximum of 7.5v. You can get 6v from four alkaline "AA", "C" or "D" batteries in series, or 7.5v from five in series.

If the LED has a flat spot on it's rim, that's the cathode (more negative) side.
If it doesn't have a flat spot, the side with the internal reflector is the cathode; you may need a magnifier to see it.

Image from: http://acept.asu.edu/courses/phs110/expmts/exp13a.html
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#4
11-20-2008, 12:22 AM
 marcolisi Junior Member Join Date: Nov 2008 Posts: 15

thank u guys for the unswers.
I will let you know the results as soon as I open the camera and get out of it the leds.

Thank u so much
Marco
#5
11-20-2008, 02:44 AM
 marcolisi Junior Member Join Date: Nov 2008 Posts: 15

Hi guys,
I want share with u the servicemanual of my sony trv-67.

http://rapidshare.com/files/165529881/CCDTR17.pdf

I am trying to look at the specs relater to the IR light emitter of the camcorder. I hope to find the part number and maybe understand more about the IR emitter specs.

If u have time, can u give a look at it and help me with some advice based on the specs of the IR led ?
I can not find easilly the specs of the ir led

Thank you

Last edited by marcolisi; 11-20-2008 at 03:09 AM.
#6
11-20-2008, 04:49 AM
 SgtWookie Expert Member Join Date: Jul 2007 Location: In the vast midwest of the USA; CST Posts: 22,030

You won't be able to get the specifications of the IR LED from the service manual.

It will simply give you a Sony Authorized Part replacement number. They even do that for resistors and capacitors. It's not hard to figure out what you might replace a resistor or capacitor with, but semiconductors become dicey propositions.

They don't want you to buy parts from anyone but them.

They also don't want people stealing their design.

Using the cryptic "house" part numbers makes it more difficult to reverse-engineer their products.
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General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input.
#7
11-20-2008, 01:04 PM
 marcolisi Junior Member Join Date: Nov 2008 Posts: 15

Thank u.

I was thinking to get the part number of the leds and google it.
In the past I bought and fixed another sony camcorder in this way.

I would like to buy some extra ir leds, in case something happen to them, when I am trying to test them to find out the voltage and resistor to use.

Can u pls help me in finding the part number of the led ?

I have problem in looking through the sevice manual that I shared with u guys.

Thank you
#8
11-20-2008, 04:56 PM
 SgtWookie Expert Member Join Date: Jul 2007 Location: In the vast midwest of the USA; CST Posts: 22,030

This is YOUR project. Don't expect others to do all the work for you.
__________________
General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input.
#9
11-20-2008, 05:56 PM
 marcolisi Junior Member Join Date: Nov 2008 Posts: 15

I am a novice...

I thought that forums are for asking questions, sharing ideas and interest.

I guess that is not what you think a forum is.
I am sorry to use your time but I always tought that when someone come up with ideas/project andneed help and get help in a foum, other people , that surf the forum, can get ideas of help from a thread....

Thank you anyway.
I hope there is still someonelse willing to help me
thanks
#10
11-20-2008, 11:24 PM
 Audioguru Banned Join Date: Dec 2007 Location: Ontario, Canada Posts: 9,411

The voltage of the IR LEDs doesn't matter unless you don't have enough voltage. You must limit the current, not the voltage.
You will never find out the spec's for the LEDs so just measure or calculate the current in the original product and do the same in your circuit.

 Tags find, led, voltage

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