Explain with sketch the operation of power MOSFET.

Ans:

Circuit diagram:

 (Structure of power MOSFET as shown below or any other equivalent can be considered ) 

V-I characteristics: 

Operation:

Figure 1 shows the construction of N – channel power MOSFET

• The Power MOSFET has a vertically oriented four layer structure of alternating P and N type (n+ p n – n + ) layers.  

•  The P type middle layer is called as body of MOSFET. In this region, the channel is formed between source and drain.  

•  The n- layer is called as drift region, which determines the breakdown voltage of the device. This n- region is present only in Power MOSFETs not in signal level MOSFET.  

•  The gate terminal is isolated from body by silicon dioxide layer.  

•  When the positive gate voltage is applied with respect to source, the n-type channel is formed between source to drain n allowing electrons to flow.  

•  Hence a positive gate voltage sets up a surface channel for current flow from drain to source.