What would be the simpliest buffer amplifier design in this situation?

Question

Take a look at this schematic:

It is important to assume that we have the following constrains:

1) Load is connected to ground, therefore it requires a positive potential to activate

2) The voltage potential to the load is at 5V regulated supplied lets say by a voltage regulator L7805CV that can supply the appropriate current (i know the load on the schematic is 380 omhs but please don't mind that)

3) Signal comes from an external low current 5V source, and we want logic 0v=off 5v=on

For this logic normally an N-channel mosfet would do the job but since the load would have to be connected to its source the mosfet will not fully saturate therefore the voltage going to the load will be a lot less than 5V.

Using a p-channel mosfet is ideal the way the load is connected but the logic will be inverted. So the simplest thing in my mind is to basically invert the input to its gate. But how do i do that with minimal components/lowest cost/simplicity?

Also is there a better way to do this than what i am thinking?

edit: In addition, is there any way i could employ a specific N-channel mosfet as my main buffer into my design while keeping the same constrains? i.e. Allow the mosfet to fully activate keeping the load connected to its source?

Kind regards!

Answer 1

A simple way is to add an nmos or transistor driver to the PMOS. It would look something like this:

^{simulate this circuit – Schematic created using CircuitLab}

If you want to use a bjt rather than a mosfet just add a resistor to from the signal to drive it:

Adjust R2 to increase or decrease speed the PMOS turns on or off.

This will gives you more topologies for inverters.

Answer 2

You can use a single-bit inverting buffer like 74AHC1G04. You could also use a single transistor and resistor. But the 1-gate inverter is probably just as small (SC70 package), just as cheap (below $0.10 in volume), and less hassle to design.