You can get power MOSFETS that can handle very high load currents. They are used in most switched mode power supplies (SMPS) like all PC power supplies and here they handle very high currents. In SMPS the MOSFETs switch at high frequencies and here a high percentage of the power dissipated in the MOSFET is actually not dissipated during on mode, but in while switicng between on- and off modes.
But if you just use it instead of a realy and not for a PWM circiut, then then you don't have to worry much about swithing losses, here you dissipate all the power in on mode.
QUOTE=Andrew_C;1288360]Any recommended part numbers for the MOSFET? I normally use 2N2222A transistors. Saving on components would be nice.[/QUOTE]
You should look for N-channel power MOSFETS. The lower RDS(on) (resistance from drain to source in on mode) the higher current the MOSFET will be able to handle - and the larger and more expensive it will probably also be. The good thing is that MOSFETs for car applications only have to handle 12V, so instead of picking a MOSFET that can handle high volatages, pick one that has low RDS(on) instead.
When you know the RDS(on) and the current you load is going to draw you can easily calculate how much power is dissipated in the MOSFET while it on.
Let's say you have a 1 Ampere load and a MOFET with an RDS(on) of 0.1 ohm.
You can for example look for a suitable N-channel power MOSFET here: https://ec.irf.com/v6/en/US/adirect/...N=0+4294841672
International Rectifier is one of the biggest manufacturers of power MOSFETs.
But try to check which N-channel power MOFETs your preferred electronic componets store sell and pick one of these.
It's also important to chose a MOSFET with low enough Gate-Soruce threshold voltage for your input signal to be able to turn it on.
The Gate input impedance is virtually so high that you draw zero current from your input signal. This also means MOSFETs are very sensitive damage from static electricity, especially before you have monutented it in the circuit.
When switching inductive loads like fans, remember to ad a flywheel diode to protect the MOSFET from back-EMF.
Read this tutorial:
The MOSFET as a Switch
If you want to use an opto-isolator you can get MOSFETs circuits with build in opto-isolator that can handle both a.c. and d.c. loads. There are also know as photovoltaic relays: https://ec.irf.com/v6/en/US/adirect/...N=0+4294841620
IR has a photovoltaic relay that can handle continuous load currents up to 6 Ampere DC, packed in a small 6-pin DIP package: https://ec.irf.com/v6/en/US/adirect/...ame=PVN012APBF