LED Tester?

[Dr. KillGood]

So I saw these LED tester devices, can you use them to find out what current you are supposed to put into a LED?

As in start at the lowest current and move up till the LED works? Or is that bad for the LED?

[WhatULive4]

So I saw these LED tester devices, can you use them to find out what current you are supposed to put into a LED?

As in start at the lowest current and move up till the LED works? Or is that bad for the LED?

I think it is actually pretty common practice. If you get a batch of random led's, i can't think of any other way to test them.

[Dr. KillGood]

Well whats a good one?

[WhatULive4]

I don't know. I would probably use a potentiometer starting at the highest resistance so it would lower the current. Ohm's law, I=V/R aka the higher the resistance the less current there will be.

[gannon]

You could use a regulator with variable voltage and current (can't remember the part number off the top of my head). Not too expensive IIRC.

[timmeh87]

If you hook up a variable resistor, the LED will 'turn on' at any voltage above its junction voltage, thats about 2.2v for red and 3.6v for white. At maximum resistance a few microamps might get through and you wont actually see anything, even though it is technically on. As you turn the resistor, the light will probably become visible around the 1 miliamp range. Beyond 20mA it wont get much brighter, but the color may start to change a little.

The only way to see how much current and LED 'needs' is to read the datasheet. It will happily take whatever current you put into it from the point where you cant see it to the point where it melts into a blob. If you just want to come up with a rough number, let me save you some time: 20mA for everything thats not superbright, 40mA for superbrights.

So from there, I hope you know the calculations by now. Incase you dont, here it is.

(Input voltage) - (LED volatage)
------------------------------------- = The resistance you need.
Led current (20mA)


To determine LED voltage, just go by a datasheet for one of the same color, as color is mainly what determines voltage.