Overview

Field-Effect Transistor (FET) is a semiconductor device widely used in switching circuits. Common field-effect transistors include MOSFET and JFET. In this article, we will use MOSFET to describe a simple switching circuit.

Following are the components of a basic N-MOSFET:

  • N-MOSFET: Select the appropriate MOSFET according to your needs, considering its maximum voltage, current, Rds(on) (drain-source resistance when turned on) and other parameters.
  • Load: Resistive, inductive or capacitive load that needs to be controlled.
  • Power supply: Provides power to the load.
  • Control signal: A signal used to control the switching state of the MOSFET. Usually comes from a microcontroller, logic gate or other control circuit.

Following are the switch circuit steps for a simple N-MOSFET :

  • Connect the load to the drain of the MOSFET.
  • Connect the positive terminal of the power supply to the other end of the load, and the negative terminal of the power supply to the source of the MOSFET.
  • Connect the control signal to the gate of the MOSFET. When the control signal is high, the MOSFET is turned on and the load gets the power; when the control signal is low, the MOSFET is turned off and the load is disconnected from the power.
  • Add a pull-down resistor (such as 10kΩ) between the gate and source of the MOSFET to ensure that the MOSFET remains off when the control signal is disconnected.
  • If the voltage of the control signal is low (such as 3.3V), you may need to choose a MOSFET suitable for logic level control, or use a drive circuit to increase the voltage of the control signal to a level sufficient to drive the MOSFET.

Summary

This is a simplified N-type MOSFET switch circuit. In actual applications, other factors may need to be considered, such as MOSFET protection, drive circuit design, power supply and signal line filtering, etc. In addition, P-type MOSFET can also be used to design a switch circuit, but the connection method and control logic will be different.

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