# Power Supply Calculation

Discussion in 'The Projects Forum' started by krishnan_hari83, Feb 14, 2012.

1. ### krishnan_hari83 Thread Starter New Member

Feb 11, 2012
21
0
Guys,

Please clarify my doubt.

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

2. ### R!f@@ AAC Fanatic!

Apr 2, 2009
8,785
771
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.

3. ### wmodavis Well-Known Member

Oct 23, 2010
737
150
For series - 12 V @ 120mA
For parallel - 4 V @ 360mA

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

4. ### mcgyvr AAC Fanatic!

Oct 15, 2009
4,784
973
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)

5. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
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.