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Based on my research so far, MOSFETs are understood to have relatively large gate capacitance, or more specifically a charge density required to operate making the capacitance a function of the driving voltage. The gate needs to be 'vigorously' pulled high to charge the gate, and then vigorously drained to discharge the gate, all for rapid and efficient switching. To this end I have prototyped a circuit with two transistors, pulling the gate to gate voltage or ground, buffered by a capacitor. The components would be sized to charge or discharge the gate in an appropriate timespan. This I understand is at least in principle what a gate driver is doing. Is this correct? Are there more nuances to consider?

schematic

simulate this circuit – Schematic created using CircuitLab

J Collins
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  • You kind of have the opposite problem in your application, but many gate drivers will include a charge pump or some other way of getting Vgs to some reasonable level with lower-voltage supplies or for high-side switching. – vir Nov 02 '21 at 18:18
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    You have a source follower circuit and this doesn't usually lend itself to doing what I think you might want. In fact the circuit doesn't make much sense; you might get 12 volts across the load but that's about it and the MOSFET is going to get red hot and burn. In fact, I amend that; you might get about 1 volt across the load. Maybe you have a cunning plan with this circuit so, please explain. – Andy aka Nov 02 '21 at 18:20
  • The intent is to have a capacitor maintaining 18 V from the divider, and alternately switching the transistors to either dump the capacitor into the gate or dump it to ground. My expectation is that the gate would be rapidly pulled to near enough 18 V or 0 V in the circuit. The answer below would suggest the transistors are on together, which clearly wouldn't work. My question has a NOT gate. Note I may have the load on the wrong side of this MOSFET. – J Collins Nov 03 '21 at 08:58
  • @Andyaka I see what you mean about the source follower now, that the gate voltage can't get higher than TTL. – J Collins Nov 11 '21 at 14:31

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There is a good explanation on this forem, check out BJT push-pull for a MOSFET it well documented. I think this will answer your questions.

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Gil
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