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I try to switch on/off IKEA Ledberg LEDs which are powered with 24 V using the setup from this tutorial video: https://www.youtube.com/watch?v=sVyi7yWuXxs

I use a IRLB8721PBF MOSFET. When I switch the output from HIGH to LOW the LEDs shine a little less brighter. When the pin is set to HIGH I can measure 23,4 V at the LEDs and when it's set to LOW I measure 22,9 V.

So the MOSFET is not really switching off but why? I also tried to put a 100 kOhm resistor between Gate and Source which also did not help.

Do you have any hints for me?

Cheers, Oliver

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    Maybe you wired the MOSFET wrong. Please show your wiring and schematic (a video that you "followed" is not good enough).
    – Majenko
    Nov 4, 2017 at 21:10
  • You should not treat a MOSFET like a relay. That is, the video shows a working 12 volt circuit but you are going for 24 volts. The amount of possible current from drain to source is dependent on the voltage of the gate with respect to the drain. You simply doubled the drain voltage but are still using the same 5 volt swing on the gate. If you do not want to study the MOSFET Characteristics Curves, that's fine. But then you should consider using a solid state relay instead. (Essentially, you are asking how to build a solid state relay.)
    – st2000
    Nov 4, 2017 at 21:39
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    Heya, first of all, let me thank you for your answers. As you can see my knowledge is quite basic. The question is not whether I want or do not want to study MOSFET characteristics curves. I simply wouldn't know how to interpret them at the moment. It's like: googling is easy when you know what you are looking for... Anyway, I think using a relay would be more suitable in this case. I'll give it a try. Thanks again! :-)
    – H0ttenburg
    Nov 4, 2017 at 22:49

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