Electronics > Beginners
Is my MOSFET switch design sane?
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digsys:

--- Quote from: Oaklander ---The FET must be surface mount and switching frequency won't be a problem. I will be well under one hertz.
How about this one? It should withstand much more current than needed, the Rds(on) is very small and the Vth seems to be low enough.
--- End quote ---
Much lower Rds(on) = 30mW = bugger all. (compared to 140mW). For extra margin, thicken any D/S tracks to take up any free space.
Leave the center part of the tracks exposed, for greater heat dissipation to free air. ie mask them off.
Lt_Flash:
Well, usually that's why you're checking not only max current in datasheet, but also thermal characteristics. This particular MOSFET can cope with 3A:

VGS = 4.5 V; Tamb = 100 °C [1] - 3 A

With Note 1 saying: [1] Device mounted on an FR4 PCB, single-sided copper, tin-plated, mounting pad for drain 6 cm2

So if you have a look at thermal characteristics, calculate required heatsink to keep junction temperature below maximum - it should do just fine.

Lt_Flash:
Sorry, my mistake in regards to heat sink - I thought that's already a TO-220 package. But anyway, if junction temperature would be less than 150C - it should be just fine.
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