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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

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    \$\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 Mar 26 '17 at 13:36
  • \$\begingroup\$ you should check this question out : electronics.stackexchange.com/questions/36098/… \$\endgroup\$ – Florent Mar 26 '17 at 13:38
  • \$\begingroup\$ The datasheet you linked is not for a IRL540N, but for a IRLZ44N. Which are you actually using? \$\endgroup\$ – marcelm Mar 26 '17 at 13:48
  • \$\begingroup\$ there is your question's answer here \$\endgroup\$ – AHIVO Mar 26 '17 at 13:59
  • \$\begingroup\$ Sorry about the datasheet, must have copied a wrong link, here is the datasheet - infineon.com/dgdl/… \$\endgroup\$ – Lyubomir Lyubenov Mar 26 '17 at 15:01
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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.

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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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