Problem Driving MOSFET with GPIO Pin

RE: Problem Driving MOSFET with GPIO Pin

hmolesworth — Thu, 14 Feb 2019 15:52:38 GMT

Multiple issues maybe .. first 4.5 volts is way above the maximum rating for the nRF52832:

Table 8: Absolute maximum ratings
Min. Max. Unit
Supply voltages
VDD -0.3 +3.9 V
I/O pin voltage VDD ≤3.6 V -0.3 VDD + 0.3 V V
VDD >3.6 V -0.3 3.9 V V

Second when the FET is off the ultrasonic would backdrive GPIO-D0 if the Nano were changed to a lower VIN of <3.6 volts. A preferable circuit to turn on the Ultrasonic would be a FET in the supply, not the Gnd return, or often simpler just a low-dropout LDO with an Enable. With dual supplies two FETs are normally used if not using an LDO.

RE: Problem Driving MOSFET with GPIO Pin

puff — Wed, 13 Feb 2019 21:12:18 GMT

any progress with your project? I suspect the reason is the voltage on drain should be higher than on gate for the mosfet to work (could be wrong though). however, in a similar schematic, but with a separate power supply for the load (with a way higher voltage), it did work just fine!

RE: Problem Driving MOSFET with GPIO Pin

RK — Wed, 01 Aug 2018 21:37:06 GMT

can't instantly see anything wrong with that, but can't find the specs of the mosfet to check Vgs on. Don't quite see the point of R1, that's just going to bleed current when the GPIO is on, I'd have a small resistor in series with the gate to stop inrush current but not as a voltage divider. Can't see it wouldn't work though.

You said you tested by supplying the gate from the battery, did you give it the full 4.5v from the battery or just the 3v (3.3v) you'd actually get from the GPIO?

Just another check question, you are setting the GPIO as output and setting it high, not just using the pull-up (which would then voltage divide with R1). Didn't seem likely but worth asking.

RE: Problem Driving MOSFET with GPIO Pin

stheinema — Wed, 01 Aug 2018 15:32:41 GMT

RE: Problem Driving MOSFET with GPIO Pin

ketiljo — Wed, 01 Aug 2018 09:31:12 GMT

How is the mosfet connected, can you show a schematic of this part only?