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  1. crutschow

    MOSFET 12VDC Relay?

    Here's the LTspice simulation of the circuit with an opto:
  2. crutschow

    MOSFET 12VDC Relay?

    With the optocoupler, you likely don't need Q7. Just connect the opto output emitter (pin 3) to ground and the collector (pin 4) to M1's gate (with R1 of course). But depending upon the gain the of opto, you may need to reduce the value of R2 or increase the value of R1, to fully saturate the...
  3. crutschow

    MOSFET 12VDC Relay?

    I forgot to include a protection diode in case the load has some inductance to absorb any negative transient when it is turned off. Revised schematic below:
  4. crutschow

    MOSFET 12VDC Relay?

    That's fine. Just make sure the epoxy is compatible with electronic parts and won't corrode them.
  5. crutschow

    MOSFET 12VDC Relay?

    Yes, R3 limits the base current, which is required for a BJT. R4 is mainly to absorb any base leakage current and insure it stays fully off, especially if the device experiences higher temperatures.
  6. crutschow

    MOSFET 12VDC Relay?

    To turn the P-MOSFET ON when the control signal is high, you can add an NPN driver (example below). The MOSFET has negligible current leakage when off (<1µA).
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