[simpits-tech] Resistor for LEDs?

[fitchett]

You require a separate resistor for each LED.  What will happen with a
common resistor is that one LED will avalanche and light up first, drawing
all the current through itself, burning out in a few seconds.  Then the
LED with the next lowest forward voltage will conduct all the current
for a few seconds, and so on.  The probability of all the LEDs having a
forward voltage close enough is very unlikely.

Chester


> Q2.  I understand what you are asking.  He wants to know that if he set
> up a power strip (i.e power coming into a bus bar with multiple
> connecting site to feed power to multiple LED's) would he need to have a
> resistor for each LED or could he put one resistor between the bus bar
> and power line?  I believe you would need to use a resistor for each
> LED, as if you start lighting several LED's, you will be running an
> increasing current through that one resistor as the multiple LED's
> produce an increasing load.  If the resistors wattage is rated high
> enough you could probably get away with just one, but I think it would
> be safer to use a 1/8 watt resistor for each LED.
>
> Any one disagree?  I'm no electronics expert but this is what I plan on
> doing.
>
> Jay
>
> -----Original Message-----
> From: simpits-tech-admin@simpits.org
> [mailto:simpits-tech-admin@simpits.org] On Behalf Of Stig Joergensen
> Sent: Monday, December 23, 2002 1:18 PM
> To: simpits-tech@simpits.org
> Subject: RE: [simpits-tech] Resistor for LEDs?
>
> Mike
>
> q1:
>
> do you know this law: U=R*I that is Voltage = Risistance * Amps
>
> you need a voltage drop of 5-3.2 = 1.8v and the amps is about 18ma this
> will give you 1.8 = R * 0.018 eg. R = 1.8/0.018 = 100 ohm
>
> q2: i dont understand what you are asking?
>
> /Stig
>
>
> -----Original Message-----
> From: Mike Williams [mailto:mikewilliams3@comcast.net]
> Sent: 23. december 2002 19:53
> To: simpits-tech@simpits.org
> Subject: [simpits-tech] Resistor for LEDs?
>
>
>
>
> Going to be using a PC power supply for my LEDs for my pit, using the 5v
> line, what
> resistor would I use to bring the voltage and amps down to 3.2v, second
> part
> of the question, if I feed a terminal strip with the 5v line to feed all
> the
> lines to the LEDs, (panel backlighting) could I use just one on the
> incoming
> 5v line, or would I use them on all lines from the terminal strip to
> each
> LED, sorry if this question is simple, I'm just not much of an
> electronics
> guy.
> Thanks
>
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