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I have a relay based audio line-out switching circuit. To drive the relays I was thinking of using a switch with an nMOS, but the issue was that when the switch is floating, both nMOS can conduct. I was thinking of cascading 2 nMOS's to operate like a pMOS since I can't find one that conducts at logical level in my area. I added a schematic below.

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ First M2 and M3 (and M1 and M4) will never turn ON it this arrangement. You need a Vgs voltage that is larger than the thredshold voltage of the MOSFETs. Thius one will always be 0V. Second, the intrinsic diode will always conduct and turn on the coils always. Is it GND on the top of the coils? \$\endgroup\$
    – Tyassin
    Commented 16 hours ago
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    \$\begingroup\$ Please follow normal schematic convention of positive voltages on top and ground/negative on bottom. Yours is "upside down". \$\endgroup\$
    – winny
    Commented 15 hours ago
  • \$\begingroup\$ I will keep that in mind, sorry for the mistake \$\endgroup\$
    – ion gigel
    Commented 14 hours ago

2 Answers 2

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If the switch will handle the coil current the MOSFETs serve no useful purpose and you could just connect the switch to the relays.

schematic

simulate this circuit – Schematic created using CircuitLab

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You should add the voltage at the top of the coils. Put GND at the source of M1 and M4. Only add V1 with a switch to the gate of M2 and M3 and add a pull down resistor on each gate.

Remove M1 and M4 and connect RLY2 to the drain of M4 and RLY1 to the drain of M1. enter image description here

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  • \$\begingroup\$ Oooh, and like this I only use two n-mos's instead of 4 and when the switch is floating, Vgs is 0 and so n-mos is OFF. Ok yeah, thank you very much \$\endgroup\$
    – ion gigel
    Commented 15 hours ago

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