Power MOSFET

Power Electronics

1. Power MOSFET Prepared by, Mr. A. Johny Renoald M.E., Ph.D.,

2. Symbol and Structure The MOSFET (Metal Oxide Semiconductor Field Effect Transistor) transistor is a semiconductor device which is widely used for switching and amplifying electronic signals in the electronic devices MOSFET is a four terminal device Source(S) Gate (G) Drain (D) Body (B)

3. Types MOSFETs are available in two basic forms P- Channel N – Channel Depletion Type : The transistor requires the Gate-Source voltage (V GS ) to switch the device “OFF”. The depletion mode MOSFET is equivalent to a “Normally Closed” switch. Enhancement Type : The transistor requires a Gate-Source voltage(V GS ) to switch the device “ON”. The enhancement mode MOSFET is equivalent to a “Normally Open” switch.

4. P-Channel MOSFET

5. N-Channel MOSFET

6. MOSFET Characteristics MOSFETs are tri-terminal, unipolar , voltage-controlled device which form an integral part of vast variety of electronic circuits. These devices can be classified into two types Depletion-type Enhancement-type MOSFET exhibits three operating regions Cut-Off Region Cut-off region is a region in which the MOSFET will be OFF as there will be no current flow through it. In this region, MOSFET behaves like an open switch and is thus used when they are required to function as electronic switches Ohmic or Linear Region Ohmic or linear region is a region where in the current I DS increases with an increase in the value of V DS . When MOSFETs are made to operate in this region, they can be used as amplifiers.

7. Saturation Region In saturation region device will act like a closed switch through which a saturated value of I DS flows. As a result, this operating region is chosen whenever MOSFETs are required to perform switching operations

8. Transfer characteristics (drain-to-source current I DS versus gate-to-source voltage V GS ) of n-channel Enhancement-type MOSFET Current through the device will be zero until the V GS exceeds the value of threshold voltage V T Under this condition, even an increase in V DS will result in no current flow Once V GS crosses V T , the current through the device increases with an increase in I DS initially ( Ohmic region) and then saturates to a value as determined by the V GS (saturation region of operation)

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