Ahh good point about the turn off. The only time I used this system was on a 12v device as a reverse polarity connection "diode" and it didn't have the back driving issue of the capacitor.There are P-channel mosfets with very low T.H point suitable to 1.9v to 3.2v range so that the gate can be tied to ground. The problem is (and I tried it) that the mosfet doesn't turn OFF when the batteries are removed because that the Vgs still exists from the power supply input capacitors. The mosfet diode has no influence because the drain and source were in the same potetial.
That's the easy bit, the MCU just turns the FET off regularly for a brief period and checks if the battery is still connected. It needs one MCU pin to control the FET and one mcu pin to sense the voltage on the battery side of the FET.That's the chicken and the egg question. How the MCU will know that the batteries were removed in order to switch the mosfet gate to turn it off?
That's a great idea. simple and low cost solution.That's the easy bit, the MCU just turns the FET off regularly for a brief period and checks if the battery is still connected. It needs one MCU pin to control the FET and one mcu pin to sense the voltage on the battery side of the FET.
by Jake Hertz
by Jake Hertz
by Duane Benson