The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Sprinklered equipment 26-008
by bigpapa
Today at 04:24 PM
On Delay Relay with Auto Reset
by Potseal
Yesterday at 09:59 AM
Wow, that was close!
by jraef
11/28/16 07:06 PM
Earthquake in New Zeeland
by RODALCO
11/27/16 11:25 PM
Calling all Non-US members!! (Non-US only)
by Tjia1981
11/27/16 06:33 AM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 15
HotLine1 10
Texas_Ranger 8
Trumpy 8
sparkyinak 7
Who's Online
0 registered (), 218 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#179355 - 07/08/08 04:11 PM Bi-Colour LED pin-out?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Hi there folks,
I was recently given about 50 10mm dual(Red/Green) colour LED's as the control boards they came off had failed and were going to be discarded.
Being a person that doesn't like stuff seeing stuff like this go to waste, I said I'd like the LED's, for some future project.
Now, here is the problem, these LED's have 3 wires on them, Red, Black and Yellow, I tried a 1.5V AAA cell on one of them, between the red and black wires and got a faint red glow from the LED, so far, so good.
I connected the yellow(+ve) and black wires to the battery and....nothing.
Is the voltage I'm using too low or too high?
I can only find data for 5mm LED's on the Net and it states Vforward should be about 1.4Vdc.

Cheers,
Mike.

Top
#179358 - 07/08/08 07:00 PM Re: Bi-Colour LED pin-out? [Re: Trumpy]
NJwirenut Offline
Member

Registered: 09/15/01
Posts: 816
Loc: Bergen County, NJ
A green LED takes slightly more forward voltage than a red one. Probably in the neighborhood of 1.8 V or so.

An LED will not put out any light unless you apply enough voltage to forward bias the junction. A single 1.5V dry cell will not be able to light a green LED.

An LED also needs a series resistor to limit the forward current. If you exceed the forward current rating, the LED will quickly overheat and die.

Top
#179359 - 07/08/08 07:34 PM Re: Bi-Colour LED pin-out? [Re: NJwirenut]
JoeTestingEngr Offline
Member

Registered: 11/04/05
Posts: 786
Loc: Chicago, Il.
http://www.rohm.com/products/databook/led/pdf/spr-54.pdf
Hi Mike,
NJ beat me to it but I agree that the battery that you used was a little light for the job. A Fluke on diode check is a great way to check LEDs. You'll find that it takes slightly more voltage to bias green Vs red as shown in the above link. That is also reflected in observed meter readings. As long as you are sure of LED polarity, you can use a 9V transistor radio battery and about 700 ohms to establish around 10mA as a safe test current. But 9 volts could exceed the reverse breakdown voltage on an LED that you are not sure of. In that case, better to use 2 of your dry cells in series with about 100 ohms as a safe test setup. I haven't noticed an LED with < 5 volts reverse breakdown voltage. In short, take the voltage source you have, subtract 2V for the LED. Divide the remaining voltage by the biasing current that you desire (10mA is good) to get the ballpark resistor value. Reds or greens will boldly reveal their true identity, while whites or blues might seem a liitle shy with their higher forward voltage. (Note: 3 volts wouldn't be enough to check blues or whites)
Joe
Of course, now I see that the datasheet I linked to shows a max reverse voltage of 3V. Also, here is a link to 1, 10mm Red/Green LED
http://media.digikey.com/pdf/Data%20Sheets/Lumex%20PDFs/Ssl-lx100139IGW.pdf


Edited by JoeTestingEngr (07/08/08 07:45 PM)

Top



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals