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Finding an LED's foward bias and current requirements?
I have a bag of bargain infrared LEDs that I'm trying to wire. I have 3 legs composed of 6 parallel LEDs. The legs are connected to one another in series. The LEDs will be epoxied into an acrylic sheet. I have an old AC adaptor that gives off 5.3V with no load and is rated for 1 amp output. I also have a 25-Ohm Potentiameter and an assortment of resistors.
I don't know the forward bias voltage or the current requirements. My RadioShack multimeter reads about 1.1V on the diode test, but I have yet to see them draw less than 1.2V in various experiments I have done.
How can I determine the current and voltage I can safely run into these LEDs? I'm trying to optimize brightness without wearing them out too quickly.
Thanks!
Also, the specs for a Radio Shack IR LED are 100mA and 1.2V.
A good target current value for an unknown LED is 10 mA. The drive voltage will depend on the color, with red requiring lower voltage than yellow or green. Use your AC adaptor with a series resistance of about 400 ohms to check your LED's; that will supply enough current to light them without cooking them. Running LED's in parallel is a bad idea; the current between them is likely to be unbalanced. If you want to use your adaptor to run eighteen of the things, I suggest wiring them in series pairs, along with a suitable current controlling resistor (about 200 ohms) for each pair, which will result in a total current draw of about a tenth of an amp, for which your adaptor will do nicely.
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