LED + resistor assemblies in parallel
Posted 26 April 2012 - 02:48 PM
My question is regarding where the + of each assembly connects to... Does it run back to the power source, or simply from the + leg of the LED assembly preceding it?
LED ratings are
1 x red @ 2.1v drop and 50mA
1 x Blue @ 3.2v and 30mA
1 x green @ 3.5v and 30mA
Posted 26 April 2012 - 02:53 PM
Posted 26 April 2012 - 02:55 PM
I'm not an electrical wizard by any means but I assume that if you do the same thing then you will have the same result.
Posted 26 April 2012 - 03:01 PM
running one led after another is in series not parallel.
does that help?
Posted 26 April 2012 - 03:03 PM
Posted 26 April 2012 - 03:06 PM
So wiring them all up in parallel will keep them in their own "curcuit, unaffected by the voltage and current demands of the others, right?
Posted 26 April 2012 - 03:13 PM
yea i should draw you a pic but i dont have time haha
yea the voltage across all 3 seperate parts will be te same but the current will divide among the 3 circuits (I think from memory thats how it works)
Posted 26 April 2012 - 03:18 PM
top is series - bottom is parallel
The way I read Eliot is you want to connect the positive legs of thr LED's together as per the bottom diagram..
Posted 26 April 2012 - 03:19 PM
This is a horrible 2 sec paint drawing so hopefully it makes sense.
Each LED and resistor combo is connected to the battery independently. You can view the circuit as 3 seperate circuits that just happened to be connected to the same battery.
Posted 26 April 2012 - 03:22 PM
You could do it like your top drawing but due to the differing specification of each LED you'll end up with different brightnesses. Ie. different colour LEDs need different amounts of current to achieve the same brightness.
Posted 26 April 2012 - 03:39 PM
KK, yeah you're pretty much on to it now. The bottom one is the correct technique. Except you need to add the current limiting resistors inline with each LED before it joins back up to the main wire.
Yeah the bottom one was what I was trying to explain in my first post - I suck at explaining myself well.. sorry guys..
Posted 26 April 2012 - 03:46 PM
I'm using a 9v battery but it is only for a couple minutes max. I'm using number 3 in any case. And would number 1 not work given the voltage drop would be too much?
Posted 26 April 2012 - 03:49 PM
Number 1 would work, but if your battery was at 9.6V instead of 9V, you would have 100mA through the red led and 60 through the green ones.
Number 3 will be fine with the current resistor values. If your battery is at 10V, you will be running 32.5mA through the green or blue led instead of 30mA... aka nobody cares.
Posted 26 April 2012 - 03:52 PM
Or just use roughly the correct value (can go up or down) as you are only running it for 3 minutes and they will happily run at slightly higher current for a few minutes
Posted 26 April 2012 - 03:54 PM
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