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Old 01-27-2004, 09:50 PM   #21
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Correct on the current limiting resistor (this is sort of what we call a voltage divider).

As for the voltage going through the LED - it's a little different. It's not really proprotionate to the applied vlotage as the device is really a semiconductor. It therefore has a performance curve. For example let's say you started applying a forwad voltage to the LED (by forward in this case I mean positive to the positve lead and negative to the negative lead). From 0 to about 2.8 V (for a Blue LED) the LED will look as if it has infinite resistance - i.e. it is an open circuit. Then as soon as you cross that threshold (the forward voltage minimum) the LED will start conducting big time. I.e. lots of elctrons will start moving across it's substrate and its conductor. This sort of looks like a big spike on the curve. It will then level off and then at about 4.5 V (it's forward voltage max) it will likely breakdown and flip again to an open circuit.

Also, since they are diodes in essence, they have reverse ratings as well. For example for a Blue LED the reverse max volts is about 5V. that means if you apply a reverse voltage (positive to the negative and negative to the positve) of 0 to 5 V they will look like an open circuit, i.e. infinite resistance. Oddly enough they are stronger in handling reverse voltages and currents then forward voltages (a charactersitic of all diodes). For example the reverse current max on most leds is 100mA while the Forward Current max is 20mA

As for confusing, agreed, it is confusing, however, I look at it this way - the electricity is simple (sort of like water flow), its the devices and how they react with it that are complex (like the pumps, elbows, tees and valves).

HTH

Tom
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Old 01-28-2004, 12:54 AM   #22
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You leave me with no questions to ask.

Spectacular info, Tom. Thanks for sticking it out and helping me through it. Kudos to you, my friend.
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