How to reduce current without reducing voltage

Hi, I'm working on a sign that basically has LEDs as letters. I have 140 LEDs that I'm planning to put in series of 4 each and then 35 in parallel.

My problem is that I was mailed a transformer that outputs DC 12v 1.25 A (Actually 12.3V 1.4A). The current is too large for what I need for the LEDs and I don't want them to burn out too quickly so how would I drop the current without affecting the voltage?

Any advice would be appreciated, thank you!

ytan10 (author) 3 years ago

*I have read a lot of comments saying that a source will only output as much current as the circuit requires, but my fear with that is that I don't know how much current LEDs draw, if they do have a maximum at all.

The problem may be that the transformer may not provide enough power to light up all of your LEDs. Search for any online "LED calculator" ( http://led.linear1.org/led.wiz is one) that will figure out what resistors and configuration you need. You do have to do some research to figure out the specs of the LEDs you have on hand (forward operating voltage for the different colors, I don't know if you are using a microcontroller or something to flash the LEDs so 20 ma draw might be a good figure to start out with, etc). Use specs from something that matches what you have. Good luck.

ytan10 (author)  caitlinsdad3 years ago

Thank you for the input, the LED calculator was actually pretty helpful. The LEDs have a very large forward voltage range so I'm not too worried about whether or not they will light up.