We know that MOS tubes are voltage-type devices and triodes are current-type devices. Generally speaking, MOS tubes can only be turned on when their driving voltage is higher than the minimum value of their dead zone voltage Ugs. However, this value is different for different MOS tubes, usually around 3-5V. However, this is only the state of just being turned on, and the current at this time is still very small. The driving voltage required for the MOS tube to reach a saturated state is generally around 6V~10V.

Here we have to mention MCU. The output voltage of MCU IO is generally 3.3V. This voltage may not be able to turn on the MOS tube, so MCU cannot directly control the MOS tube. At this time, transistors must be used. The base voltage of the transistor can be turned on as long as it is higher than the dead zone voltage of Ube. The dead zone voltage of silicon transistors is generally 0.6V.

Since the load-carrying capacity of the transistor is not as strong as that of the MOS tube, it is generally chosen to connect the MCU to the transistor and then control the MOS tube to control the load device.

Next, let’s see how it works?

When I/O is high, the transistor is turned on, the gate of the MOS tube is pulled down, and the 1.8V power supply is turned on;

When I/O is at a low level, the transistor is not conducting, the MOS tube is not conducting, and the 1.8V power supply is not conducting.