I always get tied up in all of the different properties of MOSFETS when I go shopping for them, so I'm going to be a n00b and ask for help.

I need a logic-level power MOSFET to drive four of the following vibration motors with a PWM output of an ESP32:
https://www.vybronics.com/erm-cylindrical-vibration-motors/encapsulated/v-z7al2b1692082

The PWM will be outputting linear ramp and pulse signals (i.e. ramping up from off to full voltage in 5-10 seconds and then pulsing on and off every half second or so). I know the motors are only rated for 3.6VDC, but they run just fine (for over an hour) without overheating when connected directly to a lithium ion battery. So, I will be using up to 4.2VDC of voltage.

Cheaper is always better, and a product with both a SMD and through-hole package would be ideal so I can do some prototyping before making a formal circuit board.

Thanks!

 

Cheaper is always better, and a product with both a SMD and through-hole package would be ideal so I can do some prototyping before making a formal circuit board.

The cheapest I've found is AO3400 and AO3401, surface mount only, about $0.02 each from AliExpress. For prototyping, I use a SIP adapter:

If you buy from AliExpress, don't buy too many at one time. You never know if you'll get what you ordered.

 

The max current of your motors is 250 mA and typical current is about 180 mA. Your ESP32 much like an ESP8266 is a 3.3 volt device. The problem becomes driving a logic level MOSFET gate with about 3.3 volts. Since motor current at even max is low at 250 mA I would use transistors like an NPN 2N2222 which are very common and cheap. Amazon I can buy 100 of them for about $7.00 USD. Use them for low side switching of your motors. The 2N2222 has a max current of 800 mA.

Also, wasn't it also you who wanted wireless with this project?

Ron

 

The problem becomes driving a logic level MOSFET gate with about 3.3 volts.

It won't be a problem if the MOSFET VGS threshold is about 1.5V right? And this low VGS threshold mosfet usually have relatively low total gate charge that you won't need a gate drive circuit.

 

It won't be a problem if the MOSFET VGS threshold is about 1.5V right? And this low VGS threshold mosfet usually have relatively low total gate charge that you won't need a gate drive circuit.

Yes as long as you can find a MOSFET keeping in mind in this application the max full load current and the VGs. I simply suggest a plain jane 2N2222 transistor which is more than adequate for the load mentioned.

Ron

 

Sorry to be so behind on responding to my own thread. One detail that wasn't mentioned on the datasheet I linked was the stall current (most of the datassheets are in Chinese, and the one I picked in English failed to include this spec). Here is a sheet for a similar motor:
https://www.ineedmotors.com/vibrati...bration-motor/world-s-strongest-vibrator.html

The stall current is a max of 0.75A, and I have four motors. That's a max of 3A, but let's add a little more as a safety factor and call it 5A.

So, I need a logic-level power MOSFET that can:

1. handle 4.2V @ 5A
2. allow me to power the motors with a PWM signal
3. run the motors in either a ramp up and down pattern over the course of 10 sec or pulse on and off every half second

Honestly, the best way to help me out would be to link to a DigiKey search with the correct filters applied. I get so confused with all of the different properties that I doubt myself once I land on a MOSFET that I think will work. If someone could do that, I would actually help me learn so I can select a MOSFET in the future.

Thanks!

 

4 - 2N2222 Transistors is still the best answer.

If You are not familiar with doing a Search on DigiKey,
and further,
are not familiar with interpreting the differences between similar part-numbers,
then the "idiot-proof" answer is going to be 4 - BJT's every time.
.
.
.

 

Did you read my post #3? What gate voltage do you plan to drive the MOSFET with? This is a data sheet for a FQP30N06L a logic level MOSFET. I suggest you read the data sheet and understand the data sheet. If you are planning on driving a MOSFET even a logic level MOSFET from a 3.3 volt uC source

I need a logic-level power MOSFET to drive four of the following vibration motors with a PWM output of an ESP32:

The ESP32's operating voltage range is 2.2 to 3.6V. Under normal operation the ESP32 Thing will power the chip at 3.3V. The I/O pins are not 5V-tolerant! If you interface the board with 5V (or higher) components, you'll need to do some level shifting.

Now considering the Vgs (Gate Source Voltage) you still want a MOSFET? Your concern is the VGS , Gate-Source Voltage. This is why I suggested a 2N2222 transistor to drive your motors.

Ron

 

4 - 2N2222 Transistors is still the best answer.

If You are not familiar with doing a Search on DigiKey,
and further,
are not familiar with interpreting the differences between similar part-numbers,
then the "idiot-proof" answer is going to be 4 - BJT's every time.

Well, now... that was one of the most passively condescending messages of all time.

I didn't say I wasn't familiar with doing a search on DigiKey nor that I had trouble understanding part numbers. Rather, I have been having trouble selecting the right properties for my project.

For example, I just went through to search for suitable MOSFETs, and... wait, why did the "logic level" filter go away? What did I select that eliminated all of the logic level products? (In the back of my head: should I even use the logic level filter? Maybe the products aren't all tagged correctly, so perhaps using that filter eliminates most of the ICs I should be considering?)

Basically, I'm questioning my own understanding of the different MOSFET properties based on the results DigiKey returns, so I thought I would be safe and ask here before buying something. If that makes me an idiot, then so be it.

@Reloadron, I'll be using a TinyS3 board which has its own regulator and can run from LiPo batteries directly. So, the PWM should be a max of 3.3V to the gate, right? From there, I need something that can handle 4.2V @ 5A from drain to source to power the motors.

Lastly, I'd strongly prefer a single MOSFET vs a string of 2N2222s. Maybe I shouldn't have included my comment about "inexpensive" - I'll pay a few dollars for the right part, but I just don't need some specialty $10 chip.

 

Zero Condescension intended.

"Idiot-Proof" solutions can be life-savers,
and sometimes they're even very profitable.

We ALL learn by making mistakes,
I know I certainly do,
if You don't, then you're extra-special,
( now that might be Condescending, depending on the circumstances ).

Just wait till You find-out that you're going to need a 2N2222 to turn-off that FET in most cases.
.
.
.

 

Just wait till You find-out that you're going to need a 2N2222 to turn-off that FET in most cases.

This is a great example of an unproductive comment. I'll wait for someone who is willing to help me learn and give me a hand regardless of my level of stupidity (perceived or otherwise).

The reason I posted on this forum was because I am already fully aware that I'm an idiot who needs some help. Simply reminding me of that fact is telling me something I already know, and it certainly doesn't help me or anyone else who may come across this thread.

 

Yeah, right,
that's why one of the regulars here,
that certainly has more experience than me,
gave it a "Thumbs-Up".

It would appear that You already have a pre-conceived notion of
the very best way to achieve your desired goal.

When other, more experienced people,
try to explain to You the possible downfalls of doing it a particular way,
You should at least take that idea into consideration,
and then ask why one method may be better than another.

By being humble,
You will receive a much larger quantity, and quality, of assistance here,
that's just the way life works.

But if You start-out with "demands" and "entitlement", things will start going downhill quickly.

You paid ZERO for some potentially extremely valuable experience.
.
.
.
.
.

 

I too have struggled with the MOSFET selection process. Luckily I usually tend to switch simple relays and small loads so it's relatively easy to find something that will work.

One thing I have found to be helpful is to study the graphs instead of the numbers. One of the problems with logic level MOSFETs is you usually need to drive the gate at least 4V to fully turn them on. 3.3V will get you part of the way, but for a high current load it will cause it to heat up.

Unless I did something wrong this is about the biggest selection you are going to get for a 3.3V drive. https://www.digikey.com/en/products/filter/single-fets-mosfets/278?s=N4IgjCBcoGwAwyqAxlAZgQwDYGcCmANCAPZQDaIAzAOwAcAnIyALpEAOALlCAMocBOASwB2AcxABfImHoMkIVJEy5CJciDgsp4RpXmLl+IqUgUALA3p6iZ+nDC0QRAKyvK9JyBhgzAJmqe3mbOEERB1GYs7FyQvAIi4tq+CI7QIJzcAKrCghwA8mgAsngYOACu-HieZdwAap4AtiLcZgB0vpJJ6g3EOGh4XMwSQA

Unfortunately none of them are through hole parts, and I didn't look at the package sizes or sort by size so there may be a few that are just too small to work with.

Although I still use them (FETs) from time to time I have learned myself that a simple NPN like mentioned already is a more economical choice most of the time.

 

Sir, you came into this conversation by being nasty and not being helpful in the least. I made no "demands" - I was providing my design specifications. I was asking for help. You came in paddling the douche canoe for some reason.

If you reread your first message, you basically said, "Here's a simple solution for you because you're clearly a moron who can't understand anything complex. Providing an explanation for my solution or being helpful in any other way would be a waste of my time because you're an idiot." I don't see that as a helpful answer from someone with experience.

If you would like to step off of your high horse for a second to share your knowledge, I would still really appreciate it, but so far, I haven't found your engagement on this thread to be particularly helpful in the slightest.

 

@geekoftheweek - that was actually white helpful. Thank you! Looking at the remaining results helps me see what values I SHOULD have been using as filters, but since I misunderstood what some of those values meant, I was using the wrong filters/values. I appreciate it!

Also, thank you for the note about the gate voltage. One of the filters on DigiKey was for "logic level 4V gate" or something like that. I thought that maybe I wouldn't get the right results using that filter, so I mucked with other properties that had 3.3V as a filterable value... which made the "logic level 4V gate" filter go away. This made me question my selections and my understanding of MOSFET properties (and is why I decided to ask for help the way I did).

Much appreciated!

 

Follow-up question. Should I be concerned with the continuous drain current since the motors in my project can potentially draw 3A, or does this property mean something else? If so, what?

 

Let's look at this 2N2222 idea.

Let's assume that we are using 4 transistors, one for each motor.
Stall current is 680 mA (from the datasheet) then I would choose a value of about 60 mA base current (1/10 the IC max, approx. to be in saturation)

You can see the problem already... you are not gonna get 60 mA from an IO pin, much less 240 mA with all of them on.

 

Look at using Toshiba SSM3K341R,LF MOSFET.

Maybe split the load, 2 FETs for 2 motors?
You want to make sure that a jammed motor doesn't smoke your drive.

There never is a perfect solution, just a reasonable one.
Most of the time, your PWM ramp up will keep the currents much lower.

 

That makes sense, @Sensacell - thanks!

 

I have a few more general MOSFET questions regarding the different parameters that I don't fully understand:

1. Continuous drain current (Id): Is this value independent of Vdss? It seems odd that this wouldn't be tied to the voltage
2. Power dissipation (max): How is this related to the continuous drain current? I don't understand why MOSFETs have a separate rating for wattage and continuous current since wattage is dependent upon current
3. Vgs(th) (max) @ Id: I don't understand this parameter at all
   1. First, the "@ Id" portion - why isn't the value the same as the continuous drain current? Doesn't "@ Id" mean "at the continuous drain current (from the other column)?"
   2. How does the voltage value relate to the Vgs (max) and drive voltages?
4. Rds on (max) @ Id, Vg: Some of the same questions as the previous - why are the Id and Vgs values not the same as the values in other columns?

It seems as if many of these parameters should be related or share values from other columns, but they don't. This is another thing that confuses me when looking at MOSFETs.