# LED power supply?

I need some insight on powering 2 separate circuits. Here's what I have so far......

Circuit #1.   80 3.3v  leds consuming 400MA.
Circuit #2.   20 2.0v leds consuming 60MA.

Now my power supply output is 15v - 600ma, will this power supply suffice wired parallel?

I do have a 9v-1a power supply too that could power circuit #2 if need be. but for simplicity of things i would like to use one power supply.

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mpilchfamily5 years ago
In a series parallel arraignment circuit 2 will draw between 180mA and 240mA depending on how the LEDs and resistors are arranged.

As for circuit number 1 you are trying to use way too many LEDs. Trying to use all those LEDs on a single 15V power supply will require 8A to run it. Worste yet is how much power will be flowing through the resistors. You will need to find 4.7 Ohm resistors that can dissipate over 750mW. It would be a good idea to reduce the number of LEDs in circuit 1 and use lower power LEDs.

Use this handy LED calc to help you figure out the best series/parallel arrangement for the LEDs and see how much heat dissipation the LEDs and resistors will need to handle as well as how mush power will be drawn from a given power source.
ARGMISTER (author)  mpilchfamily5 years ago
That calculator is how i got my information.... and i can split circuit #1 is acctually 4 seperate circuits but can still be considered one on how its set up...it will be technically 4 batches of 20.

8 amps seems to be alot for LEDS.....even at that quantity but im not at all informed on circuits....so idk.

he wizard says: In circuit 1.

each 100 ohm resistor dissipates 40 mW
the wizard thinks 1/4W resistors are fine for your application Help
together, all resistors dissipate 800 mW
together, the diodes dissipate 5280 mW
total power dissipated by the array is 6080 mW
the array draws current of 400 mA from the source.

The wizard says: In circuit 2:

each 270 ohm resistor dissipates 108 mW
the wizard thinks 1/4W resistors are fine for your application Help
together, all resistors dissipate 432 mW
together, the diodes dissipate 800 mW
total power dissipated by the array is 1232 mW
the array draws current of 80 mA from the source.

5 years ago
The 8 amps comes from you putting "400mA" at the end. The assumption is that that is how much current EACH diode draws since the first two stats were per LED. I assume the LEDs are actually ~20mA each.

Are you trying to power both circuits off of one power supply? In theory you should be fine, just don't mix up the resistors.
ARGMISTER (author)  bwrussell5 years ago

I would like to power them off one supply just to simplify the circuit but its not a requirement. I do have a smaller 9v supply i could power the red ones with.

This is a "Music to led project" BTW. Do you think 2 tip31 transistors will work for this setup or would 5 be better?

("The 8 amps comes from you putting "400mA" at the end")

OK i understand, ....Yes they are 20ma ea. just your generic red and blue leds....I meant the whole circuit consumes 400ma and 60ma.
5 years ago
I would try using just one, if that doesn't work ad the second supply.

Honestly I have no idea what goes into a circuit like that. I would look up one of the many similar projects here and see what they did. If all else fails, ask another question.
ARGMISTER (author)  bwrussell5 years ago
Yea i did a lil google searching and i think ill be fine with 2. I have built a few very small circuits like this but with only 20 leds....not 100!! Ill figure it out. trial and error!!!
Jack A Lopez5 years ago
Why don't you just draw a diagram of it.  Then calculate the voltage at each node, and calculate the current through each branch, and then you'll have your answer.