NMOS with Negative Vds: Exploring Effects

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This is known as bidirectional conduction.In summary, we learn that an NMOS can operate in both directions as long as the Vgs turn-on voltage is maintained. This is because the MOSFET's channel is bidirectional and either end can act as the source. However, the MOSFET is normally only connected one way to avoid conduction in the substrate diode. As long as this diode is not forward biased, the MOSFET can work in both directions.
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Hello. We learn that an NMOS is in the triode region for Vds < Vgs - Vth, and in this case the drain current has a given expression. My question is, is this also valid for Vds < 0 ? What happens in this case?
 
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A MOSFET's channel is bidirectional so it will conduct equally well in both directions as long as the Vgs turn-on voltage is maintained. From a physics point of view either end of the MOSFET can act as the source, it just depends upon the relative voltages. The reason they are normally only connected one way is to avoid conduction in the substrate diode which has the anode connected to the source and the cathode connected to the drain in a N-MOSFET. As long as you don't forward bias that diode the MOSFET works in both directions.
In short
Almost all discrete MOSFET has built-in parasitic diode (body diode with cathode on the drain, anode on the source for N-channel). This diode will not conduct until drain voltage will be lower then the source voltage. If Vds > -0.6V body diode is OFF. So until the diode is OFF you can swap the drain and source.
 

Related to NMOS with Negative Vds: Exploring Effects

1. What is NMOS with Negative Vds?

NMOS (n-channel metal-oxide-semiconductor) with negative Vds (drain-to-source voltage) is a type of transistor where the voltage at the drain terminal is lower than the voltage at the source terminal. This creates a reverse bias condition, which can have various effects on the transistor's behavior.

2. What are the potential effects of Negative Vds on NMOS?

The effects of Negative Vds on NMOS can include changes in the transistor's threshold voltage, amplification, and switching speed. It can also lead to increased leakage current and reduced breakdown voltage.

3. How does Negative Vds affect the threshold voltage of NMOS?

Negative Vds can decrease the threshold voltage of NMOS, making it easier for the transistor to turn on. This is because the negative voltage at the drain terminal attracts more electrons to the surface of the semiconductor, reducing the depletion region and allowing current to flow more easily.

4. Can Negative Vds cause damage to NMOS?

In most cases, Negative Vds will not cause any permanent damage to NMOS. However, if the negative voltage is too high, it can lead to breakdown and permanent damage to the transistor. It is important to operate NMOS within its specified voltage range to prevent damage.

5. How can NMOS with Negative Vds be used in practical applications?

NMOS with Negative Vds can be used in applications where a reverse bias condition is desired, such as in amplifiers and switches. It can also be used to create voltage references and voltage regulators. However, proper circuit design and voltage control must be implemented to prevent damage to the transistor.

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