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I am creating a light control circuit with a low-power tilt switch (>0.1A) to automatically turn lights on and off when the switch is tilted. When the switch is level, it is open, and I want the lights to be on. When the switch is tilted, it closes, and I want the lights to be off. I had originally planned to use a transistor with a NOT gate after the switch, but I read about depletion mode MOSFETs and I think an N-channel depletion MOSFET might do what I need it to. Would this circuit accomplish that?

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Any type of MOSFET will retain a charge on the gate when the gate is not connected to anything. This is unlike a BJT which requires a continual current flow through the base. A MOSFET circuit must have a resistor to discharge the gate when the switch is off; or you can use a double-throw switch so that one side of the switch discharges it \$\endgroup\$
    – user253751
    Mar 25, 2023 at 7:57

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It does not work because the current keeps flowing through the depletion nMOS when VGS=0V and when VGS=12V.

enter image description here

Note, you need to add a resistor from nMOS gate to ground to define the gate voltage to 0V when the switch is open.

To solve your problem, you can just change the location of the switch and the resistor and use a normal nMOS

enter image description here

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  • \$\begingroup\$ Perfect, thank you so much! \$\endgroup\$
    – Raddy
    Mar 25, 2023 at 15:49

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