Tuck3rz,
I will do my best to help you understand....
A MOSFET (metal oxide semiconductor field effect transistor), or any transistor can act like a switch.
Which is what it will be doing here in your circuit.
The "gate" (aka 'base') only requires a minute amount of current to effectively 'switch' the mosfet/transistor on. That is what the 1K resistor is for. To heavily limit current.
This is what your microcontroller will do. When you 'set' the ouput (logic 1), the MOSFET will turn on, allowing current to flow through the Drain to the Source (or if it were a transistor from the collector to the emmiter)
To put it simply,
- Output of Microcontroller goes high,
- MOSFET turns on (closes)
- Current flows from your 12v source through the big resistor, through the LED, through the MOSFET, to ground.
The low resistance resistor (4.7R @ 25W) is there to limit current seen as though the LED and MOSFET dont have much resistance...
It is only a small amount of resistance to allow a large amount of current to flow. That is why it needs to be rated at least 25W, becasue there will be alot of current passing through it.
Hope that makes it abit clearer....
2A LED hey... that one massive LED...
Got a photo? hope you dont mean .2A or even 2mA???