The gate
of a MOSFET requires a relatively large amount of charge to drive the
voltage up to the ON state, and down to the OFF state. An inaccurate but
close enough way to say this is that the Gate to Source has a large
amount of capacitance.
To charge this capacitance quickly when using PWM drive, it may require a charge/discharge current of several amperes. A microcontroller output won't drive this. So a special chip that is capable of sourcing and sinking several amps is used. The chip won't sustain that current for long, but it doesn't have to.
If this is not done, then it will take a lot longer to switch the MOSFET fully ON or OFF. During this time, the MOSFET will be dropping considerable voltage while large currents are flowing, resulting in a lot of waste heat in the MOSFET. This wastes power and heat stresses the MOSFET.
It can be something as simple as a couple of transistors, a PNP and NPN connected as push-pull drivers.
Often a third input transistor is added, so that Vcc can be greater than the drive voltage and so a 3.3V or 5V logic signal can drive a 12V gate drive. Most MOSFETs require at least 10V to be full ON, otherwise something called a logic level MOSFET must be used that is fully ON at 5V gate drive.
Or specialized MOSFET gate driver ICs may be used for much higher drive currents.
To charge this capacitance quickly when using PWM drive, it may require a charge/discharge current of several amperes. A microcontroller output won't drive this. So a special chip that is capable of sourcing and sinking several amps is used. The chip won't sustain that current for long, but it doesn't have to.
If this is not done, then it will take a lot longer to switch the MOSFET fully ON or OFF. During this time, the MOSFET will be dropping considerable voltage while large currents are flowing, resulting in a lot of waste heat in the MOSFET. This wastes power and heat stresses the MOSFET.
It can be something as simple as a couple of transistors, a PNP and NPN connected as push-pull drivers.
Often a third input transistor is added, so that Vcc can be greater than the drive voltage and so a 3.3V or 5V logic signal can drive a 12V gate drive. Most MOSFETs require at least 10V to be full ON, otherwise something called a logic level MOSFET must be used that is fully ON at 5V gate drive.
Or specialized MOSFET gate driver ICs may be used for much higher drive currents.
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