# Power Supply Calculation

#### krishnan_hari83

Joined Feb 11, 2012
21
Guys,

I am having 3 LEDs each of 4 V and 120mA.

What is the power supply I must give under the following conditions.

1. 3 LEDs connected in series
2. 3 LEDs connected in parallel.

Kindly advice me of the power supply calculation.

Krishnan.H

#### R!f@@

Joined Apr 2, 2009
9,747
In series u will need more than 12V @ 120mA max & one resistor.

In parallel u will need 4V @ 120 X 3mA
But I doubt this way would be advisable.

#### wmodavis

Joined Oct 23, 2010
739
For series - 12 V @ 120mA
For parallel - 4 V @ 360mA

But as R! suggests best to have resistors which will limit current.

#### mcgyvr

Joined Oct 15, 2009
5,394
I always wonder how many millions of LED's have been destroyed in the past 10 years because people think you can just hook them up like a light bulb and off you go..

Your power supply could be rated for 100V @ 50 Amps and still work just fine provided you include some sort of current limiting into your schematic (like a resistor in series with the LED to limit the current or other constant current supply)

#### studiot

Joined Nov 9, 2007
4,998
You might like to consider a series connection of two parallel pairs.

That way you can run from a 9V battery and a 4R7 half watt resistor.