I cannot find a mosfet that will do this at room temperature. So I am going to change the way I do this (a little). First of all, I am using the Following method to validate the mosfet for my application. Please tell me if something is wrong here.
Vbus - DC Bus Voltage (applied to soruce pin of mosfet)
Iload - Load current (also current from source pin to drain pin of mosfet)
Ids - max current (given as a function of Rds(25)
Tamb - Ambient temp inside the enclosure
Pdisp(a) - Power dissipated in the mosfet (ambient)
Tmax - Max Junction Temp
Rtheta(ja) - Temp rise per watt of dissipated power (junction to ambient)
Rds(a) - Resistance at temperature (junction) (given in graph)
So,
The equations are as follows:
Pdisp(a) = (Tmax - Tamb) / Rtheta(ja)
Iload(a) = sqrt(Pdisp(a) / Rds(a))
so for FCB20N60 from fairchild, whose spec says 600V, 20A:
Pdisp(a) = (150 - 40) / 40
Pdisp(a) = 2.75W
Iload = sqrt( 2.75W / 1.25)
Iload = 2.2 A
Which means I can get 2.2A out of a 20A mosfet Which means this one won't work.
Questions:
1. Does my math have errors? If so, please offer suggestions.
2. Is there actually a mosfet that will do what I want? What is a P/N?