I'm trying to drive a big LED (3W) with a MOSFET. Eventually I want to drive it with an Arduino but so far I'm failing to get the right numbers in my test circuit.
My test circuit is like this:+5 | [R1] (8 Ohms) | D G -[R2]--- JUMPER S | LED | GND I can connect the jumper cable to +5V or ground and it switches on/off as expected.
My MOSFET is one of these:
R2 is 220 Ohms (it's probably not even needed, I just put it in there while I'm testing...)
The problem is that when I connect the jumper to +5V and measure the voltage drop across each component it's not what I expect and the LED current is dimmer then it should be as a result.
The voltage drop across R1 is about 1V, the voltage drop across the MOSFET is1.5V and the voltage drop across the LED is 2.5V.
I expected the drop across the MOSFET to be very close to 0V. Does anybody have an idea why it isn't?