Switching LEDs using ULN2803

Submitted by David on Sat, 08/08/2020 - 18:32

Hi new member here and hoping somone can answer what is probably a simple question to the experienced. I am making a model project and am lightng LEDs using a nano and a ULN2803 transistor array. I am using high brightness LEDs and want to drive them at around 25mA.

At 5v and using a 68ohm resistor i get 26mA running the LED direct. Now when I connect into the circuit with the nano and ULN2803 the LED is only getting 17mA. I assume this is due to the internal resistance of the ULN chip. Will I run into any problems if I just reduce the resistor so I achieve my 25mA.

Many thanks for any advice


The Darlington pairs are rated for 500mA 50V output. It wouldn't be a problem but the 2803 will heat up.

  Joined February 12, 2018      696
Monday at 02:11 PM


I will be running 3 LEDs in parralel with their own resistor from each output pin across all 8 outputs so 600mA total. I have read that a MOSFET would be more efficient in this application, what would be a suitable logic level MOSFET array that would drop right in instead of the 2803?

  Joined August 08, 2020      1
Saturday at 06:16 PM

It will not cause problem because each individual Darlington pairs have maximum current of 500mA, 50 V.  TPL7407L is a 7-channel Mosfet array equivalent to it, speced with 600mA drain current, 40V.

  Joined February 12, 2018      696
Monday at 02:11 PM