Hi. I am implementing pretty simple FET-driven on/off switch, which should be normally closed. The idea is that when V2 drives 12V, the device (as LOAD) is not powered. So, in theory this works, but in practice... is there something obvious I should take into account?



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in theory this works, but in practice... is there something obvious I should take into account?

Are you talking about the simulation not working? Or an actual breadboard?

What is the purpose of the divider on V2?

If you want help troubleshooting your simulation, you should put some voltages on important nodes.

 

Obviously R1 and R4 are in parallel so they can be replaced by one resistor of equivalent value.
What does the capacitor do?

 

Hi. I am implementing pretty simple FET-driven on/off switch, which should be normally closed. The idea is that when V2 drives 12V, the device (as LOAD) is not powered. So, in theory this works, but in practice... is there something obvious I should take into account?

View attachment 306095

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Put a diode in series with, or instead of, R3 (cathode to Gate), and remove R4.

 

The circuit works in practice and in theory. Just benchmarking if there is something obvious I should take into account. C1 is because I have learnt that it is good practice to put a capacitor in series of gate resistor in high side/low side circuit.
R1 and R4 can be replaced by one, obviously.
I used voltage divider (R3/R4) to have some protection. V2 is a manual switch.

 

I think I will go with this. R3 gives some protection, C1 smooths the switching, gate voltage is well above the fet's switching...

 

Still see no reason for C1.
Why do you want to "smooth" the switching?

 

So, in theory this works, but in practice...

This statement made me think that it wasn't working.

I used voltage divider (R3/R4) to have some protection. V2 is a manual switch.

The gate doesn't need protection from 7V:

C1 is because I have learnt that it is good practice to put a capacitor in series of gate resistor in high side/low side circuit.

Seems unnecessary to me...