Power MOSFET Symbol:
The power metal oxide semiconductor field-effect transistor (MOSFET) is a device derived from the field effect transistor (FET) for use as a fast-acting switch at power levels. Unlike the bipolar transistor which is current controlled, the MOSFET is a voltage controlled device. The main terminals are the drain and source, the current flow from drain to source being controlled by the gate to source voltage in the Power MOSFET Symbol as shown in Fig. 11.7a.
Switching Characteristics of Power MOSFET:
The device is fully on and approximates a closed switch when the gate-source voltage is sufficiently large. The MOSFET is off when the gate-source voltage is below the threshold value, VGS (th). The idealized characteristics of the device operating as a switch are shown in Fig. 11.7b.
A power MOSFET symbol is a unipolar, majority carrier, non-junction, voltage controlled device. During the last decade, the power ratings and Power Mosfet Switching Characteristics have improved dramatically with sharp fall of prices, and it is now a main competitor to other power devices.
The high switching speed causes low switching loss, and therefore snubber requirement is very minimal. Power MOSFETs are normally used in high frequency switching applications within the ratings of a few watts to a few kWs. The device is very popular in switching mode power supplies. The state-of-the-art devices are available with 500 V, 40 A ratings.