Why can't a microcontroller drive a MOS tube directly?

First of all, the IO port of the single-chip microcomputer has a certain load capacity, but the current is very small, and the driving capacity is limited, generally within 10-20 milliamperes, so the single-chip microcomputer is generally not used to directly drive the load.

Let's briefly compare the differences between transistor and MOS transistor drives

Transistor:

The transistor is a current-controlled type, and as long as the base drive voltage is higher than the dead zone voltage of Ube, it can be turned on at 0.7V.

For the transistor, 3.3V is definitely greater than Ube, and the base current (Ib=(VO-0.7V)/R2) can be calculated according to the IO port voltage and current limiting resistor. Therefore, it is enough to connect a suitable resistor directly in series at the base and let the transistor work in the saturation region.

Processors generally focus on low power consumption, and the power supply voltage will be relatively low.

Therefore, the general single-chip microcomputer power supply is 3.3V, and the maximum voltage of its IO port is 3.3V.

MOS Tube:

The MOS transistor is a voltage-controlled type, and the driving voltage must be higher than the threshold voltage Vgs to be properly conducted, that is, higher than the minimum value of the dead voltage Ugs to be turned on.

The threshold voltage of different MOS transistors is different, generally around 3-5V. , and the saturation drive voltage is 6-8V, which is greater than the 3.3V of the IO port voltage.

If the drive is 3.3V, the MOS transistor may not open at all, or it may be in a semi-conductive state. In the semi-conductive state, the internal resistance of the tube will be very large, if the drive is small, the current load can be used, but the large current load is not allowed, the internal resistance is too large, the power consumption will be large, and the MOS tube is easy to burn.

Therefore, the IO port is generally selected to directly control the transistor, and then control the MOS transistor.

Why use a triode to drive a MOS transistor?

This is because the load capacity of the transistor is not as strong as that of the MOS transistor, and when the load current is required, the MOS transistor needs to be used.

Can that drive the MOS tube directly?

The explanation has been given above, but it is not excluded that some MOS tubes with very low power can be operated.

(Some of the above pictures and data come from the Internet)