The field-effect transistor (FET) designed as a type of transistor in which an electric field used to control the flow of current. FET devices comes with three terminals: source, gate, and drain. FETs control the flow of current by the application of a voltage to the gate, which succesively alters the conductivity between the drain and source. FETs also reffered as unipolar transistors as they permits single-carrier-type operation. This means that FETs operates either by electrons or holes as charge carriers in their operation, but not both. Field-effect transistors generally features high input impedance at low frequencies.
The FET’s three terminals are:
- Source (S): carriers enter the channel. The current entering the channel at S is denoted by IS.
- Drain (D): Carriers leave the channel. Conventionally, the current entering the channel at D is indicated by ID. Drain-to-source voltage is VDS.
- Gate (G): The terminal that modulates the channel conductivity. The drain current controlled by the voltage to G, one can control IDÂ
Among these 3 terminals, Gate terminal function as a controlling terminal. Basically, BJT acts as a current controlling device. Similarly, FET also operates as a voltage controlling device. Here, the drain current controlled by the voltage between gate and source. So, it is called as voltage controlled device. FET features high switching speed and good efficiency at low voltages. It is one of the prominent power semiconductor device in the world, due to its low gate drive power, fast switching speed, easy advanced paralleling capability, wide bandwidth. This makes it ideal for use in a wide range of applications such as in low-voltage switch.
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