I'm trying to turn on a 24V rail powering a 2.4A device using an N-channel MOSFET (
IRLB8743). I'm having an issue understanding the basics of how it's working
The MOSFET has an R
DS of 3.2mOhms, at a V
GS of 5V. The load is 10Ohms.
I tried hooking it up as shown.
The current going from the 24V power source to ground is about 0.22A, or 10X less than I expect it to be, and the MOSFET gets to about 100 degrees Celsius in about a minute while attached to a 9.6 °C/W heat sink.
On Semi's application note for MOSFETs in Load Switch Applications says that P
LOSS = I
LOAD2 * R
DS(on).
I'm not exactly sure how to get I
LOAD, but if just using Ohm's law it should be I=V/R or 24/10 = 2.4A. I'm actually only getting 10X less than that though. But even if I
LOAD = 2.4A, than P
LOSS would be 5.76 * 3.2mOhms = 18.4mW. That seems like a very small amount of power, so why is the MOSFET getting so hot?
What am I not understanding here?