a gate driver
A gate driver is a small power amplifier whose only job is to charge and discharge a MOSFET's gate fast. A microcontroller pin can set the gate voltage, but it cannot deliver the brief, large current surge needed to slam a big gate capacitor up and down in nanoseconds. The gate driver sits between the weak logic signal and the power MOSFET, taking a feeble command and pushing or pulling amperes into the gate to make the transition crisp.
Why bother? Because a slow gate transition is expensive. While the MOSFET crosses from off to on it passes through the linear region, with both voltage and current high at once, dissipating heat the whole time. The faster the gate driver flips it through that danger zone, the less energy is lost per switch. A typical driver might source and sink an amp or several, with low output resistance, so a 20 nC gate moves in tens of nanoseconds rather than microseconds.
Gate drivers also handle the awkward jobs: a high-side driver includes a bootstrap or charge pump to lift the gate above the supply rail for a high-side N-channel switch, and many add protections like undervoltage lockout and dead-time control for half-bridges. The honest reality is that at any real switching speed or power level, you do not drive a power MOSFET straight from a logic pin: you use a proper gate driver, or you pay in heat, ringing, and unreliable switching.
Replace a direct logic-pin gate drive (tens of milliamps) with a 2 A gate driver and a 30 nC gate switches in about 15 ns instead of microseconds, cutting switching loss dramatically.
A current buffer that flips the gate fast to cut switching loss.
Driving a power MOSFET straight from a logic pin works only at low speed and low power. At real switching frequencies the slow transition cooks the device.