Firstly, the I/O port of a microcontroller has a certain load capacity but a very small current drive capability, generally within 10-20 milliamps. Therefore, it is generally not used to directly drive loads.

Let's briefly compare the differences in driving between transistors and MOSFETs:

Transistors:

Transistors are current-controlled devices. As long as the base drive voltage is higher than the dead zone voltage Ube, usually around 0.7V, the transistor can conduct.

For a transistor, 3.3V is definitely greater than Ube. The base current can be calculated based on the I/O port voltage and the limiting resistor (Ib = (VO - 0.7V) / R2). Therefore, by directly connecting an appropriate resistor in series with the base, the transistor can operate in the saturation region.

Processors generally emphasize low power consumption, so the supply voltage is relatively low, often around 3.3V.

MOSFETs:

MOSFETs are voltage-controlled devices. The driving voltage must be higher than the threshold voltage Vgs for the MOSFET to conduct normally, meaning it must exceed the minimum value of the dead zone voltage Ugs.

The threshold voltage of different MOSFETs varies, generally around 3-5V, while the saturation drive voltage is between 6-8V, exceeding the 3.3V of the I/O port voltage.

If a 3.3V drive is used, the MOSFET may not turn on at all or may be in a partially conductive state. In the partially conductive state, the internal resistance of the MOSFET is very high. While it can handle small current loads, it is not suitable for large current loads. The high internal resistance also leads to high power consumption, making the MOSFET prone to burning out.

Therefore, it is generally preferred to use the I/O port to directly control the transistor, which can then control the MOSFET.

Why Use Transistors to Drive MOSFETs?

This is because the load capacity of a transistor is not as strong as that of a MOSFET. When there are requirements for load current, a MOSFET needs to be used for driving.

Can MOSFETs be driven directly?

The explanation above already provides the answer, but it does not rule out the possibility of operating very low-power MOSFETs directly.