The Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is a device used to amplify or switch electronic signals. It is a unipolar, unidirectional, voltage controlled device. The symbol of MOSFET is shown below.
Case 1: Gate is kept open.
The negative voltage applied to source terminal will make Pn+ junction forward bias. The positive voltage applied to drain terminal will make Pn+ junction reverse bias. Therefore there will not be any drain current.
Case 2: Positive potential is applied to gate
Here the gate terminal will act as positive plate of capacitor and P-substrate acts as another plate of capacitor.
When gate is kept at +ve potential, automatically the other plate induces negative charges this forms a channel (path) for electrons to move from drain terminal to source terminal.
Thus the application of gate source voltage controls the flow of drain current.
It shows relation between Vds & Id.
When Vds is increased, Id also increases, even if Vds increases furthermore, the Id remains constant.
It is applicable widely in low power high frequency converter.
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