you could use a transistor to swith the mosfet.

 

as regards darlington it is only reffered to BJTs. darligton ckt is used for high current gain. in darligton ckts source current is amplifed beta times the first transistor and this amplified current is again amplified beta times the second transistor. essentialy beta of first transitor multiplied by beta of the second transitor will be the over all gain of the darligton pair.

pls note: beta(hfe) is the current gain in common emitter mode.

 

The answer is to use the PROPER MOSFET.

Get a LOGIC LEVEL MOSFET. They saturate at 5v.

 

The answer is to use the PROPER MOSFET.

Get a LOGIC LEVEL MOSFET. They saturate at 5v.

There are plenty that saturate below 5V, some of the 5V ones are just hitting fully on at that input and there's no logic device I'm aware of that puts out a pure 5V output unless you're using CMOS, even then we've got a lot of logic devices that consider less than 3V to be a logic level 1.

Try going through a few in here, you'll find some that have quite low Rds specs at lower Vgs voltages:
http://www.mouser.com/Semiconductor...iZ1z0y3zrZ1z0z63x&Keyword=logic+level&FS=True

Your selections are about 3x as good if you can use a surface mount component.
http://www.mouser.com/Semiconductor...Power/_/N-7h7n5?P=1z0y3zr&Keyword=logic+level

 

What exactly is the load again? A Relay?

An IRLZ44 can work with 50 Amps at 50 Volts with a proper heatsink, and can be controlled by the logic line out of your uC (microcontroller). This will work perfectly well to drive a mechanical or Solid State Relay.

No other transistors needed, though a driver transistor may help with switching speeds if running at high frequency PWM.

Side Note: Most home outlets are only 120V @15 Amps. The 20 Amp 120V outlet looks a bit different, with a "T" shaped pin laying on it's side.

 

A true 20A outlet is also supposed to be on an isolated breaker instead of a branch circuit.

 

This circuit I made switches AC if you change the voltage source(near the mosfet) between 5v and -5v :

Why are thyristors used instead of mosfets/bjt to control AC?

 

Triacs can chop both the positive and negative swings of a sinewave, and for regulation they can do it at any point, so it's either a bit more silicon doping in one package, or a few packages of P type and N type FETs.

MOSFETs fail in the needed Vgs and Vds when switching at a peak, they switch only at/near zero crossing. These are what make up Solid State Relays.

 

There are a place for both since each have advantages over the other considering the circuit in which they're used.

 

MOSFET can't switch A/C loads directly.
TRIACs can switch A/C loads as they conduct both the cycles(full wave 0 to 2∏). Another advantage in traic would be you can control the conduction period of each half cycle of the A/C thus varying the average voltage.