3 ms·
>In particular, this made me sad: the 10K resistor to ground isn't strictly necessary, but it ensures that the MOSFET remains OFF if the arduino is disconnected
by pravda 10y ago
>In particular, this made me sad: the 10K resistor to ground isn't strictly necessary, but it ensures that the MOSFET remains OFF if the arduino is disconnected or it's pin is not an OUTPUT.
Not sure why that made you sad (extraneous ' in its?).
But I agree about the static-sensitive disadvantage of MOSFETs.
Also, the author mentions that a TIP120 is not a transistor but a darlington pair (two transistors in one) but then misstates the Hfe.
The whole point of a darlington is to get a high Hfe (small base current controlling large collector current) and the Min. Hfe is 1000, at least according to:
https://cdn-shop.adafruit.com/datasheets/TIP120.pdf https://cdn-shop.adafruit.com/datasheets/TIP120.pdf
- ChuckMcM 10y agoIt wasn't the grammar :-) it was that the author considered the 10K resistor to ground as "not strictly necessary". It is critical if the microprocessor pin can float (tri-state). Without it, and a floating gate, not only will the FET eventually turn on, it can be damaged by excess charge build up.
- simcop2387 10y agoNot just excessive charge up it could be possible for it to be stuck in its linear region and dissipate a lot of power as it's spuriously turning on because there's a charge on the gate. I've managed to do that one on accident with a bad motor driving circuit. Though it was also largely caused by coupling on the breadboard.
- mindslight 10y agonit: It's not wrong to assert that the microcontroller software will prevent the output pin from ever floating. And the gate's voltage will be constrained between Vdd and Vss due to the output pin's likely body diodes. Is it worth it to save a penny part, especially in a hobby/prototype design? No. Also if you throw away all your BJTs, what do you use to drive the gate capacitance of your fancy FETs?