I'm following a tutorial for creating a unidirectional motor driver on a protoboard. The author of the tutorial suggested using an SI2300 MOSFET, but I don't have any of those on hand. I do have an assortment of SMD components that includes a bunch of different transistors. Among them are S9013, SS8050, and 2N3904. The motor I'm trying to drive has a stall current of 60 mA -- yea, it's tiny.

I'm wondering if I can substitute the SS8050 for the SI2300 in this application. I understand that I'll need a current limiting resistor on the base of the BJT, where none would be required on the MOSFET. The SS8050 datasheet gives its collector current maximum rating as 1.5 A, which is way more than I need. Vce(SAT) is 0.5 V, which I understand to mean that I'd suffer 0.5 V drop across the transistor. If I'm pulling the stall current, that is 30mA, which is well below the maximum power dissipation of 1.0 W. (I'm writing this down not because I'm confident in any of it, but just to show that I've tried to do my homework.)

I'm going to try soldering this all up, because all it will cost is my time, but I would appreciate it if y'all would warn me if I'm doing something excessively silly that is going to blow up in my face.

 

For what it's worth, this appears to have worked:

https://photos.app.goo.gl/JJWxZeWUDhagd5BRA



Soldering is pretty iffy. Need more practice. And a holddown clamp because trying to solder this and hold it with tweezers at the same time was truly a pain.

The 22AWG solid core is not so much fun for this. I ordered some 24AWG stranded stuff to use in the future.

 

Glad it worked. For a bipolar transistor, the CE drop is variable, and depends on the current a bit. So your results may be different.

 

In my case the tolerance on the motor power is very wide. Despite how small it is, it is still way overpowered for what I need it to do -- it's a small toy for my kid. That said I'm going to acquire some MOSFETs and if they arrive before assembly I will remake the part.

 

Can you post the circuit showing how the transistor in question is connected to the rest of the circuit?

 

Sure thing:

 

For that motor I wouldn't even be concerned with needing a MOSFET.

If it works, leave it be.

But you do want to get a flyback diode across that motor.

 

Oh shoot. There is such a diode in the implementation (bottom component in the microscope image), I just forgot to include it in the diagram. My bad.

 

The motor I'm trying to drive has a stall current of 60 mA -- yea, it's tiny.

For that current, you may get away with 2n7000 Mosfet.

 

For that current, you may get away with 2n7000 Mosfet.

Regrettably, I don't have any of those on hand -- I only have the BJTs mentioned, which came in an assortment kit of smd components. That's why I was asking about those specific part numbers.

I'm still on my quest to acquire all the basic components that are needed for projects like this one and now I see that mosfets are among those components. So I will acquire some more of those soon.

 

Either bipolar transistor you mentioned should work fine in that circuit. I doubt R2 will be needed, but remember the diode.