# LED Driver

#### RodneyB

Joined Apr 28, 2012
697
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.

#### MikeML

Joined Oct 2, 2009
5,444
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.

#### ScottWang

Joined Aug 23, 2012
6,844
considering the LED life and brightness, you just using 80% of 25mA, that is equal to 20mA, and the limiting resistor is 56Ω.