Anyone know if LEDs are voltage dependant? I ask because the lights in my truck radio quit after I dropped the faceplate. I thought I would get some LEDs and try replacing them but I dont know if the voltage in the head unit is less than 12 volts.
Anyone know if LEDs are voltage dependant? I ask because the lights in my truck radio quit after I dropped the faceplate. I thought I would get some LEDs and try replacing them but I dont know if the voltage in the head unit is less than 12 volts.
In reply to porksboy:
It's been a very very long time since I got my E Tech degree and almost as long since I did anything with it... but IIRC a LED only has a voltage drop of .7v.... don't remember the current draw... I'm sure others can be of more help
The exact voltage for a given LED varies with the color (different semiconductor materials are used), but figure somewhere in the 0.9 to 2.5 V range. (wbjones is correct, silicon diodes run 0.7 V). The important deal with LED's is to control the current, the simplest way is with just a resistor. But more sophisticated methods will use constant current or Pulse Width/Duty Cycle controller circuits. You have to look at the data sheet for the particular device to see, as manufacturers can either string several individual diodes together inside a single package, or build-in the controller circuit.
Carter
erohslc wrote: The exact voltage for a given LED varies with the color (different semiconductor materials are used), but figure somewhere in the 0.9 to 2.5 V range. (wbjones is correct, silicon diodes run 0.7 V). Carter
told ya it had been a very very long time.... when last I worked in my field the only LED's in common use were the red ones...
So do I need to watch the voltage going in to the LEDs? If so what happens when I put ones rated for 1 volt in and put 12 volts to them? How about vicey versey?
I'll let erohisic answer for the record... but I'm betting that 12v across a 1v LED might let all it's smoke out...
As soon as there's enough voltage potential and the LED "falls over" and allows current to pass, there has to be some kind of ballast resistance in-line with the device or current will burn it up basically in an instant. The resistance curve is, as voltage rises, "infinite, infinite, ZERO".
I wonder if any of what I just wrote makes any sense... I don't work with these things really since getting out of school, at least not directly.
Look at what ero wrote above, a lot of LED packages are more complex than the simple diode that came first. If you go to Radio Shack and pay a buck for three red LED's in a little baggy, plan on them not having any inline resistance and you'll need to add something in series with them to get them to light and actually last. The data on the back of the bag should tell you what the manufacturer recommends.
You use a voltage divider since you need a resistor to limit current in the circuit anyways.
Get a 1000 Ohm resistor (1K Ohm) at crap shack when you get your LED assortment package and put it in series with the LED of your choice. That should do it. Remember that if it is hooked up "backwards" you won't get any light. So, experiment with the resistor in series. It won't hurt it to put it in backwards.
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