Electronics > Beginners

Help sizing a MOSFET

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vmallet:
I want to experiment driving a 12v/85ohm/145mA relay coil with a 5v signal using a MOSFET.
I have a ON Semi 2N7000 (60V 200mA, https://www.mouser.com/datasheet/2/308/2N7000-D-33553.pdf) and a ON Semi BS170 (60V 500mA, https://www.mouser.com/datasheet/2/308/BS170-1118810.pdf)

Would they both work just fine? Would one (or both) not be appropriate? Is one recommended over the other? Should I use another one altogether?

I'm hoping I can learn how to pluck the right info from the data sheets.

Thanks!

David Hess:
The 2N7000 is marginal at that load current with only 5 volts of drive and some units may overheat.  The BS170 is a better choice and all parts should work.

You can get this by figuring out from the datasheet by what the drain-to-source resistance will be with a gate drive of 5 volts.

Zero999:
What's wrong with a plain old BJT? The BC338 should do that, even with a miserable 3mA of base drive, it will have an on voltage of under 1V.
http://www.mouser.com/ds/2/149/BC337-193546.pdf

exe:
Just don't forget base resistor for bjt.

David Hess:

--- Quote from: Zero999 on April 17, 2019, 12:51:18 pm ---What's wrong with a plain old BJT? The BC338 should do that, even with a miserable 3mA of base drive, it will have an on voltage of under 1V.
--- End quote ---

Nothing is wrong with a BJT but vmallet asked about two specific power MOSFETs.  A 2N4401 would be my first choice but the BC337/BC338 would be equally good.

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