MOS FET reccomendations for a newbie

Question

I'm embarrassed how many times I've used ordinary BJT transistors in circuits that clearly would have been better suited to a FET, and even better a MOSFET. This is because as a lifelong hobbyist, I have a huge stash of common BJTs, and sadly the days of well stocked "neighborhood" electronic store are long gone. Experimenting always requires ordering parts first. Now I understand MOSFETS well enough to pour over specs and parameters and make choices, but maybe someone with more experience could point me to a short list of "general use" enhancement mode P and N channel mosfets that are both inexpensive and readily available as both SMT and through hole parts, that I basically couldn't go wrong ordering a supply of. I realize there are thousands of good choices, but if you consider that the old familiar (and cheap!) 2N2222 (NPN) and 2N2909 (PNP) BJTs have satisfied the bulk of my needs for simple switching or basic amplification apps for as long as I can remember, perhaps some parts will come to mind. I very seldom need to handle more that 500mA, and usually have low voltage and power requirements (15VDC, seldom more than 1W). Honestly most of my needs are for switching and about the only 'specialty" wishlist item I have is that the lowest "on resistance" would certainly be worth a few cents more. Suggestions welcome.

Answer 1

If you're into lower voltage (logic level, 3.3V) and such like circuits, the old standards such as the 2N7000/7002 (latter is SMT) are not great.

You might want to look into Alpha and Omega's line of SOT-23 MOSFETs which are good value and good performance. For example, AO3418/AO3419. You can get 100 of them for about $20, so even if you sneeze and a few of them go walkabout it's not a disaster.

Unfortunately, there's not much that's good introduced in through-hole packages in recent years at least for smaller than a TO-220.

MOSFETs have evolved rapidly, and the best available MOSFET of several years ago is often overly expensive and of poor performance compared to more modern parts.

Answer 2

Honestly - the days of the "standard" part number are gone as more manufactures put out products, and we're given the luxury of choice. Every person I talk to, has different recommendations. Additionally, its hard to find a part that has both SMT and Through Hole variants. For example, my go-to is BSS138, but I believe they only come in SMT.

You seem to have the specs you need in mind. I'd type them into DigiKey, and find a part that has the best package and value for your needs and then just go with that.

Answer 3

First, you have to get over looking for parts that have thru hole variants. Hardly anything does anymore, and there's no point to them anyway. Soldering a SMD part is actually easier than soldering a thru hole part.

My common N channel FET goto part for low voltages is the IRFML8244. This is a great little part. It's cheap, and better in just about all respects than its predecessor, the IRLML2502, which was my preferred jellybean part for such things before. The IRFML8244 can handle up to 25 V, 41 mΩ Rdson at 4.5 V gate drive, can pass a few amps, has relatively low gate charge, and comes in the common SOT-23 package. You can drive this FET directly from a processor pin without any additional parts in many cases. It's great for switching solenoids, motors, and the like.

For high side switching, you have to look around. Do a search on Mouser for your requirements. You will find less parts that cover a variety of applications without more compromises or higher price.

Answer 4

MOSFETs are a little unlike BJTs in that while just about any BJT can be substituted for any other device (so long as the parameters are in the ballpark), MOSFET circuits typically depend on a particular Vt. This is because for the most part BJTs are characterized by the beta parameter, but it is considered poor design to assume a particular beta for a circuit, as significant variations can occur even given the same part number.

This is different than MOSFET devices, where Vt can be (relatively) more precisely controlled. With that said however, the 2N7000 is apparently notable enough to warrant its own Wikipedia page, so it must be pretty common.