Enhancement FET's have a threshold voltage, Vt or Vgs(th) that must be exceeded by at least 2x above threshold to achieve rated current as a switch. This means as V+ switch or high-side-switch that Vgs must be;
- Vgs boosted with a charge pump well above the load V+
- replaced with a Pch FET and open drain Nch driver
- re-designed as a low side switch
The Nch switch needs a gate voltage higher at least twice it's switch threshold above the load voltage to be a high side (+) switch. Therefore it makes more sense to use it as a low side switch.
The error newbies, often make, is to assume the gate threshold is adequate to switch rated load current. Vgs(th) is just the threshold of conduction often rated at 250uA, hardly enough and has a wide Vgs range. Therefore choose Logic Level Nch FETs to switch on the low side of the load (-).
Choose a part with Vgs(th) is < 1/3 of your logic level output for good results. Thus if logic output is 3.3V consider an Nch FET with Vgs(th) < = 1.1V
simulate this circuit – Schematic created using CircuitLab
There is such an off-the-shelf multiple output IC as type 1. above with 8 separate logic level inputs and 8 power N ch outputs, 0 to 500 mA and up to 50V.
- There also exist commercial 4ch and 8 ch opto-isolated relay cards that are inexpensive online.