Operation of a P channel MOSFET

  • Thread starter akhil123
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  • #1
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Main Question or Discussion Point

Why is it that a P channel MOSFET is always operated with Vds < 0 i.e source positive with respect to the drain? The book says that carrier always needs to flow from the source to the drain, but would the reverse operation harm the MOSFET in any way? Please explain. Thanks.
 

Answers and Replies

  • #2
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What is the carrier in the PMOS channel? What needs to happen in order to form the channel? Compare with an NMOS channel and I think you'll have an answer.
 
  • #3
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Conduction in the inverse direction along a MOSFET channel is generally possible. This is utilised in some types of synchronous rectification, and also in some analogue switches.

What is not possible, at least for most (all?) discrete devices, is for the MOSFET to block a large reverse drain-source voltage. This results from the parasitic body diode, which is reverse biased in normal operation, but will conduct if the polarity is reversed.

The situation of a MOSFET inside an integrated circuit is different, because it may be possible to return the body to a remote potential, so as to maintain the body diode reverse bias.
 

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