There are three designs of complementary switches, which means that when the button is closed only one of configurations conducts the current and activates the circuit and the other circuit will remain inactive. On the other hand, this action will be reversed when the button is not closed.

The purpose of these designs is to isolate both VCC and GND. They are not intended to work at high frequencies. Assume that these switches are on/off switches which are intended to connect or disconnect both the VCC and GND of each circuit from the main VCC and GND of the board.

10K resistors are pull up or pull down resistors which prevent the gate of the MOSFET from floating. The 1K resistors are gate resistors which prevent high currents damaging the MOSFET.

Which design is better for this purpose?

If there is a better circuit for this purpose, could you please provide the schematic?

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  • \$\begingroup\$ fig1 won't work...wrong FET types. The rest seem reasonable. \$\endgroup\$
    – Aaron
    Oct 28 '21 at 14:34
  • 2
    \$\begingroup\$ Define what you mean by "isolate". There will be some small leakage through the FETs, so they are not isolated like an air gap from a relay. \$\endgroup\$
    – Aaron
    Oct 28 '21 at 14:36
  • 2
    \$\begingroup\$ None of these are what I'd call isolated, as there's always the body diode connecting them even if the FET were somehow able to provide perfect isolation. \$\endgroup\$
    – Hearth
    Oct 28 '21 at 14:44
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    \$\begingroup\$ 1) Instead of me explaining what is wrong with many of these circuits (like the top MOSFET conducting while the bottom one is not conducting), I suggest to put these circuits in a simulator (like LTSpice) and see what happens. 2) realize that disconnecting GND and VCC of a circuit can result in issues, especially if that circuit has a connection to other circuits that are not powered down. Can you explain WHY the circuit needs to be isolated (which as explained in other comments, it actually is not). \$\endgroup\$ Oct 28 '21 at 14:51
  • \$\begingroup\$ When cutting all of the supply rails, you should first cut the positive rail, then cut the GND. In all the figures shown, I don't see anything to perform this priority. So neither is best or better than any other. \$\endgroup\$ Oct 28 '21 at 14:56

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