Electric OU: Supplement: MOSFETs… How do THEY work? Chapter 2

A simple circuit describing high-side switching using a random N-channel mosfet. Also showing that the gate needs only Charge to switch and if the Charge stays on the gate it keeps the mosfet ON. (Note: there’s one point where I say “drain” when I meant to say “source”. Darn that Ben Franklin anyway. Touching the SOURCE (ground, negative, electron source) to the gate discharges the positive charge (lack of electrons !) on the gate and turns the mosfet off. Touching the DRAIN (positive, the place where electrons drain away) to the gate provides the positive charge (lack of electrons !) to turn the mosfet ON. I can also pull electrons out of the gate (providing a positive charge !) just by touching the gate pin even though the 1 meg resistor. There… if you are confused, you can thank Benjamin Franklin for me.) The FG is set to make a slow flash at about +/- six volts or so. When the mosfet has sufficient charge on its gate, the signal from the function generator is passed through from drain to source…NOT through the gate. But the function generator is providing BOTH the positive charge (at negligible current) for the gate AND the much more substantial current to light the LED. The gate charge is added and subtracted from the gate each time the function generator signal changes polarity so the mosfet IS switched on and off when the gate pin is connected to the drain pin … or, if the gate is disconnected, the charge simply remains on the gate and the mosfet stays ON

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