Hi everyone,
In playing around with arduino, I often need to add a mosfet here and there. I have had some lying around, but now want to purchase a bunch for general purposes.
By general purposes, it is all from motors, to solonoids to relays and whatnot.
The question is though - what is a good general purpose mosfet?
I have been using some TIP125, but what would you recommend?
Thank you in advance!
The TIP125 is a PNP darlington, which begs the question do you want an n-channel
or p-channel MOSFET or both?
For general use normally n-channel would be used. It must be logic-level,
and an on-resistance of 0.015 ohms or less is desireable. Unless you are
dealing with voltages higher than 12V go for 20V or 30V MOSFETs - the
lower the voltage the cheaper a low-resistance MOSFET is (and there
are more to choose from).
If you want p-channel for high-side switching then the supply voltage matters.
If you were switching 12V LED strips for instance then a non-logic-level
p-channel device would be appropriate, driven by a small NPN transistor
as level-shifter. If everything is 5V then logic-level p-channel would be
required.
IRL540 are popular/easy to get....
an on-resistance of 0.015 ohms or less is desireable
... but Rds of IRL540 won't be anywhere near that (datasheet says 0.077 Ohms @ 5V).
0.015 Ohms seems very low to me. Something like an HUF76137 will do it but they're not so easy to find.
Search Digikey - N-channel MOSFET for sinking current thru LED strips, motors, relay coils, etc. Logic Level, Low Rds, Low gate capacitance, In stock, low price:
39mOhm
8mOhm
5mOhm
Overall list of thru hole parts - sort by price, find 1-lot price with lowest Rds you are comfortable paying for.
Can do similar search for P-Channel. List of available parts is far smaller, and parts are pricier tho:
200mOhm
50mOhm
7mOhm
Hi,
Thank you for the response MartT. I had an idea that the TMP125 was a PNP, and that this was not what I wanted - I was not quite sure enough of that though, which is also why I asked.
Most voltages I would be switching is around 12V in most cases.
I have also used:
IRF520NPbF (http://arduino.cc/documents/datasheets/MOS-irf520npbf.pdf)
These were from the Arduino Starter Kit I got a while back - so I would assume they are recommendable. I have found them quite affordable ($0.74 a piece):
http://www.aliexpress.com/item/Free-Shipping-20pcs-lot-IRF520NPBF-IRF520N-IR-TO220-IC/1473225690.html
Are those worth using? They apparently have an on-resistance of 0.20Ohm, which is of course quite far from your recommendation.
I understand that the moment I start going for much higher loads, I may need something else, but for general purpose?
The IRL540 also seem quite good (http://www.vishay.com/docs/91300/91300.pdf), and at an excellent price:
http://www.aliexpress.com/item/Free-Shipping-20PCS-IRL540N-IRL540-IR-T0-220-IC/1366673716.html
The lower resistance when on, should mean it heats less (as I understand it), thus better at higher loads.
Are there any distadvantages over this vs the other?
CrosssRoads: Thank you for the links. I will try going through it, once I understand it all better.
Thank you for taking your time to help me out understanding all of this 
Casper
Hotcut:
I have also used:
IRF520NPbF (http://arduino.cc/documents/datasheets/MOS-irf520npbf.pdf)
These were from the Arduino Starter Kit I got a while back - so I would assume they are recommendable. I have found them quite affordable ($0.74 a piece):
No.... the IRF520 is NOT a logic level MOSFET. It cannot be fully switched on with a 5V signal.
Hotcut:
The IRL540 also seem quite good (http://www.vishay.com/docs/91300/91300.pdf), and at an excellent price:
The clue is in the name.
The 'L' in IRL540 indicates "Logic Level".
I'm using this one in a temperature controller project:
It should be able to switch pretty high loads without a heatsink. My device is 3.6 amps @ 12v.
fungus:
IRL540 are popular/easy to get....an on-resistance of 0.015 ohms or less is desireable
... but Rds of IRL540 won't be anywhere near that (datasheet says 0.077 Ohms @ 5V).
0.015 Ohms seems very low to me. Something like an HUF76137 will do it but they're not so easy to find.
0.002 ohms is very low. 0.01 ohms isn't exceptional these days.
Hi,
Fungus, thank you for that clarification! I was sure it was a logic level, considering that it is the one Arduino sent with their starter kit.
This might explain why I am having so many problems with my drink-dispensing project (solonoid not opening fully perhaps).
I will be going for the IRL540 - logic level, and seems to be easier to find than the IRLB8721PBF suggested by Planecrazy29.
Thank you all for your help with this. I believe I have gotten a somewhat better understanding of this now.
Have a great day!
Casper