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What is the significance of the body diode in the switching model of the MOSFET?

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chieeeeef

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What is the significance of the body diode in the switching model of the MOSFET? Why is there a body diode in it? Is its presence in the switching model related to its construction? These questions were raised to us by our professor. I would really appreciate it if anyone would explain the presence of the body diode in the switching model of the MOSFET. I'll be posting a picture of the switching model of the MOSFET for reference. The encircled object is the body diode of the MOSFET. Thanks in advance.

Regards,

chieeeeef
 

Re: body diode of MOSFET

Hi,

A couple of application of the body diode are as follows: If the voltage is higher on the source then the drain it will flow back through the body diode and protect the MOSFET. Also if the voltage on the Drain is lower then the Source the same protection is aforded. You will find body diodes is bipolars and IGBT for the same reason.

Regards

dfullmer
 

Re: body diode of MOSFET

Isn't the body diode just inherent in the constructon of a MOSFET?

Take an n-channel, for example, the most common one. It's an n-material drain embedded in a p-material substrate. That's a diode with drain as cathode and substrate as anode. Then, when the substrate is tied to the source, it's a diode whose anode is at the source leg with the cathode at the drain; hence, it's a diode across the MOSFET's channel, across the MOSFET itself.

To avoid the diode influence, one must select a MOSFET where source and substrate aren't connected, a four leg device.
 

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