Re: resistor transistor basics

Rich Grise wrote:
On Mon, 14 May 2007 03:01:15 +0200, Jan Nielsen wrote:

I am just wondering if the 5LEDs with the same voltage can share a
resistor, when they will be varying in current draw.

No. They never have exactly the same forward voltage drop, so one
LED will hog all of the current until it blows, then the next, and


Yes, that's the theory which apparently assumes that Vf is some unchanging
value. Now you should go out and get some LEDs and actually try it for fun.
Provided they are the same type, I'm betting that they will all light. I'm
not saying that they will all be the same brightness or they will all pass
the same current, but they will all most likely light. Vf rises with If,
they will seek some equilibrium point.

so on. The current rises exponentially with the voltage.

Thanks for setting me straight on that, I was thinking that current rose
linearly with applied voltage. ;-)

Use a resistor (or current regulator) in series with each LED, or in
series with each series string of LEDs.

Good advice.


.

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