LED Driver

Thread Starter


Joined Apr 28, 2012
I am trying to learn how to work out what LED driver to use and how to connect the LED's

I want to connect 50 LED's for example to a 12 Volt supply. The LED's have the following specifications

Vf = 2.2V
Vi = 25mA

In the past I would have used the LED calculator found at http://led.linear1.org/led.wiz

Using the above details This calcuator shows 5 LED's in Series with a 47 Ohm resistor and 10 of these arrays in Series.

I would like to be able to calculate this myself and in turn use a driver which from what I read is more suitable method.

Any assistance will be apprecieated.


Joined Oct 2, 2009
If driving 25mA LEDs, the parallel strings of 5 LEDs in series with resistors is the best way to go.

To use a proper constant-current driver made expressly for LEDs, you would have to look connecting all 50 LEDs in series, and then finding/building a driver with an open-circuit voltage greater than 1.1* 50*2.2V >= 121V.

If you split the strings in two strings, you would need two drivers, each with an open circuit voltage greater than 60V.


Joined Aug 23, 2012
considering the LED life and brightness, you just using 80% of 25mA, that is equal to 20mA, and the limiting resistor is 56Ω.