I'm not really good with electronics but i'm really trying to learn as much as i can, so please have mercy on my question :)

Hardware So, i have an Arduino Uno, a 24V 150W power supply, a 24V 48W LED strip and an IRL540N (Datasheet) mosfet.

The goal The idea is to turn on/off the LED strip using Arduino PWM. So far i have achieved that (schematic below), however i have an issue.

The issue I have partically achieved my goal, however i get voltage drop of 3.4V after the mosfert, which i dont understand. I assume that's not normal, but i cant figure out why it's occuring ?

What i've learned about the issue on my own I've been reading a lot and i've stumbled upon posts for similar usage, where it has been explained that this is a high side usage for a mosfet and needs a P channel mosfet, however i still cant figure out why. Can someone please explain why do i have that voltage drop and what am i missing ?

Notes I have 5v at the gate, and i am within the voltage and current limits supported by the mosfet. Running the gate @5V runs the LED strip @20.5V at 2A and the fet doesnt even get hot, so everything except the voltage is great and as per my needs.

Schematic enter image description here

  • 1
    \$\begingroup\$ The issue might be that you are not turning your FET on fully, because it might require a higher Gate voltage. Look up logic level mosfets. \$\endgroup\$
    – Wesley Lee
    Commented Mar 26, 2017 at 13:36
  • \$\begingroup\$ you should check this question out : electronics.stackexchange.com/questions/36098/… \$\endgroup\$
    – Florent
    Commented Mar 26, 2017 at 13:38
  • 1
    \$\begingroup\$ The datasheet you linked is not for a IRL540N, but for a IRLZ44N. Which are you actually using? \$\endgroup\$
    – marcelm
    Commented Mar 26, 2017 at 13:48
  • \$\begingroup\$ there is your question's answer here \$\endgroup\$
    – AHIVO
    Commented Mar 26, 2017 at 13:59
  • \$\begingroup\$ Sorry about the datasheet, must have copied a wrong link, here is the datasheet - infineon.com/dgdl/… \$\endgroup\$ Commented Mar 26, 2017 at 15:01

2 Answers 2


you are giving the mosfet a pwm and measuring dc voltage, you are actually measuring an average value according to duty cycle. connect the gate to 5v dc and measure a gain. if you are giving 100% duty cycle to the mosfet and the drop still exists, this may be because the mosfet is not fully turned on.


If the circuit is working correctly you should have about 0.1V across the MOSFET (from Fig. 1 in the IRL540 datasheet you linked to) so something is not right.

  • Check the gate is a constant 5V.
  • Check you have the MOSFET pins connected the right way around (source to ground, drain to the LEDs)?
  • Check the voltage is dropped across the MOSFET. You say "voltage drop of 3.4V after the mosfert" - make sure you're measuring the voltage from ground to the drain of the MOSFET.

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