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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

Lyubomir Lyubenov
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    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. – Wesley Lee Mar 26 '17 at 13:36
  • you should check this question out : http://electronics.stackexchange.com/questions/36098/selecting-a-mosfet-for-driving-load-from-logic – Florent Mar 26 '17 at 13:38
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    The datasheet you linked is not for a IRL540N, but for a IRLZ44N. Which are you actually using? – marcelm Mar 26 '17 at 13:48
  • there is your question's answer [here](http://electronics.stackexchange.com/questions/144607/do-mosfets-have-voltage-drop-across-source-and-drain-when-turned-on) – AHIVO Mar 26 '17 at 13:59
  • Sorry about the datasheet, must have copied a wrong link, here is the datasheet - http://www.infineon.com/dgdl/irl540npbf.pdf?fileId=5546d462533600a40153565fc2a62567 – Lyubomir Lyubenov Mar 26 '17 at 15:01
  • What is your PWM frequency? Can you use an oscilloscope and see what does the signal at gate look like? – Chupacabras Mar 27 '17 at 15:58
  • Unfortunately i dont have an oscilloscope. I'm really new to electronics so i dont have all the necessary equipment :) Even my multimeter doesnt have PWM support. – Lyubomir Lyubenov Mar 28 '17 at 17:26
  • Does the voltage drop exist when you drive the mosfet at 100% duty rate (e.g. connecting it straight to the 5v pin on your arduino)? Also: This is not a high-side switch. High-side: The MOSFET is on the high-side of the load (in your case, the LED strip) Low-side: The MOSFET is on the low-side of the load (as is the case in your schematic, where the Source terminal is connected to GND. – divinas Aug 02 '18 at 15:17

2 Answers2

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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.

M.Morsy
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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.
Heath Raftery
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