LED driver

[karthikeid]

hi

how to drive led and supply constant current??
circuit for driving 50led's in series/parallel @30mA per led. ???

 

[chromei386]

From what voltage source? Batteries? Power supply unit? Wall wart?

To get the right mA to your LEDs, use this formula:

R = (Vs - Vl) / I

where R = resistance
Vs = power supply voltage
Vl = sum of LED voltages (check, but probably 2v ea)  
I = LED mA = 30mA

you could hook them all up from a 12V DC source - having 5 LEDs per 'leg' and have 10 'legs' in parallel....  with some quick calculations that's

R = (12 - (5x2)) / 0.030
  = 67

so you have 5 LEDs hooked up in series with a 67 ohm resistor....... then hook up 10 in parallel with power supply.

the circuit draws 30mA x 10 = 300mA

so you just need a 12V DC power supply capable of delivering 300mA (easy to buy, find or make!)

 

[Hero999]

What voltage are the LEDs?

What voltage is the adaptor?

It's more efficient to connect them as strings of many in series, in parallel.

 

[karthikeid]

led's are 2v@10ma, i need to drive 50 leds, how do i connect in series or parallel   ???

 

[Hero999]

I thought you said they were 30mA?

What voltage is the adaptor?

Here's a site which explains the difference between series and parallel LED circuits.
http://www.ngineering.com/led_circuits.htm