Power Electronics MOSFET - Power Electronics

What is MOSFET in Power Electronics?

MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is a type of transistor which is used for switching the electronic signals. It consists of four terminals namely; source (S), Drain (D), Gate (G) and Body (B). MOSFET’s body will be usually connected to the terminal of the source(S), which leads to three-terminal device related to other field effect transistors (FET). As these two main terminals are generally interconnected using short circuit, only three terminals will be visible in the electrical diagrams.

MOSFET is an ordinary device used in most of the circuits which are both digital and analogue. In comparison with regular transistor, MOSFET requires less current (less than one mill-ampere) for switching ON. Simultaneously, it will deliver a high current load of more than 50 Amperes.

Operation of a MOSFET

MOSFET will have a thin layer of silicon dioxide which will be acting as the plate of a capacitor. Controlling gate isolation will increase the resistance of the MOSFET to exceptionally high levels. Gate terminal will be barred from the primary current pathway and therefore no current will be leaked into the gate.

MOSFETs is of two main forms

  • Depletion state – Depletion state needs a gate-source voltage (VGB) for switching OFF the component. Once the gate is at zero (VGB), the device will be usually ON and thus it will function like a load resistor for a given logic circuits. 3V is the threshold voltage to load devices with N-type depletion as in 3V, device will be switched OFF by switching the gate at negative 3V.
  • Enhancement state − Gate-source voltage (VGB) will be necessary in this state for switching the component ON. Once the gate is at zero (VGB), device will be usually OFF and can be switched ON by ensuring that the gate voltage is high than the source voltage.

Symbol and Basic Construction

mosfet_symbol.jpg

Where, D − Drain; G − Gate; S − Source; and Sub − Substrate

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