Strip LED question

Thread Starter

tracecom

Joined Apr 16, 2010
3,944
This is the third time I have written this post and had it fail to post, so I suppose it's that "title too long" gremlin.

So, before I wrote the whole thing again and lost it, I posted the first sentence and then edited the post.

Suppose I have a prefabricated strip of LEDs wired as shown in Figure A, and powered by 12 VDC. Each string of 3 LEDs draws 20 mA, for a total of 80 mA per strip of 12 LEDs. Now, suppose that the same strip must be powered by 15 VDC as shown in Figure B, but the current should not increase. I believe I could add one resistor (R9) and restrict the total current to 80 mA, but would that cause problems with the individual strings of 3?

What is the best way to hold the current at 20 mA per string of 3 LEDs given that I cannot change the value of the resistor in each string?

Thanks.
 

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Thread Starter

tracecom

Joined Apr 16, 2010
3,944
And that doesn't violate the rule against using a single current limiting resistor for LEDs in parallel? (As you can tell, I'm a tinkerer, not an engineer.)
 
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