How to use NMOS tubes and PMOS tubes to make switching control circuits
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How to use NMOS tubes and PMOS tubes to make switching control circuits

Posted Date: 2024-01-16

01 MOS tube conduction and cutoff principle

The main circuit current direction of the NMOS tube is D->S, and the conduction condition is that VGS has a certain voltage difference, such as 5V (the G potential is higher than the S potential).

The main circuit current direction of the PMOS tube is S->D, and the conduction condition is that VGS has a certain voltage difference, such as -5V (S potential is higher than G potential).

02 MOS tubes are used as upper tubes and lower tubes

1) When the NMOS is turned off, that is, the S pole (source) is directly connected to the ground, you only need to control the G pole (gate) voltage to control the conduction or cutoff of the NMOS transistor, because the conditions for the conduction of the MOS transistor depend on the voltage difference of VGS. .

2) When NMOS is used as the upper transistor, the D electrode (drain) is connected to the positive power supply, and the voltage of the S electrode is not fixed. It is impossible to determine the G electrode voltage that controls the NMOS conduction, because the voltage of the S electrode to the ground has two states, and the NMOS is turned off. It is low level when it is turned off, and close to the high level VCC when it is turned on.

3) The principle of PMOS is the same when it is used as an upper tube or a lower tube.

4) PMOS is usually used as the upper tube and NMOS is used as the lower tube.

03 NMOS tube application

Use NMOS to turn off the transistor, and the S pole is directly connected to the ground. You only need to fix the G pole voltage to 5V to conduct it (the 5V depends on the MOS tube model)

04 PMOS tube application

Using PMOS as the upper tube, the S pole is directly connected to the power supply VCC (5V), and the G pole voltage can be turned on simply by fixing the voltage to 0V.

Review Editor: Huang Fei


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