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MOSFET current direction?

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inverter

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can the current of N-chanel MOSFET flow through source to drain(not from its body diode) when the MOsfet is turned on?

Thanks!
 

ceaser

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look
all fet's are bidirectional devices
this means that the current can go from drain to source and vice versa
you can see that from the industerial shape of all fet's
 

inverter

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I mean can current flow from its chanel but not internal diode? I know a MOSFET's current can bidirectionally flows.
 

vicky

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HI DEAR,
wheer did i think you are right
 

ghosh

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yes if the the potential is not the same- meaning body is not tied to source or drain
ag
 

sheraz.pervaiz

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MOSFET is a symmetrical device that means source and drain can be interchanged(if body is not short circuited to any of the drain or source)

It is our convention that we name the terminal source which has the lower potential for NMOS.

Thus it just depend upon our convention of naming terminals which determine the direction of current flow.
 

inverter

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hi, guys, thanks for your replies, but I still can not get the right idea.
I repeat my question again,


Since all MOSFET integrate a body diode, so the current can flow from the drain to source or vice versa. while the MOSFET can not sustain negative voltage.( I mean the drain potential must be higher than source potential),or the body diode will be shorted.
now the question is :

The drain terminal is connected a positive voltage source through an inductor, and the source terminal is connected to zero potential. when the mosfet is still on, the current flows through source to drain. Is this current flow through body diode or its channel.

the MOSFET discussed here is N-MOS.\]
 

JoseLeonardo

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The MOSFET transistor is a bidirectional device, but the current can flow througth source to drain, only if the voltage in drian is bigger than source terminal. If you want learn about this devices, you can read microelectronics circuits by sedra and smith.

Added after 33 seconds:

The MOSFET transistor is a bidirectional device, but the current can flow througth source to drain, only if the voltage in source is bigger than drain terminal. If you want learn about this devices, you can read microelectronics circuits by sedra and smith.

Added after 1 minutes:

The true answer is the second, in the first answer a had a little mistake, sorry.
 

    inverter

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inverter

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JoseLeonardo said:
The MOSFET transistor is a bidirectional device, but the current can flow througth source to drain, only if the voltage in drian is bigger than source terminal. If you want learn about this devices, you can read microelectronics circuits by sedra and smith.

Added after 33 seconds:

The MOSFET transistor is a bidirectional device, but the current can flow througth source to drain, only if the voltage in source is bigger than drain terminal. If you want learn about this devices, you can read microelectronics circuits by sedra and smith.

Added after 1 minutes:

The true answer is the second, in the first answer a had a little mistake, sorry.



Thanks , but one thing I don't understand is that since MOSFET integrates a body diode, how can source voltage be higher than drain, the body diode will be shorted. so the conclusion is N-MOS, current is flow through its body diode even the MOSFET is turned on when there is current flow through Source to Drain.
 

Willt

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Hi friend,

I have some idea regarding your question. Let's consider two cases:

(1) When a transistor (NMOS) in a chip is considered, there is never current flowing from the source to the drain (PMOS is vice versa). This is because the drain is defined as the terminal with higher potential (ignore the gate).

(2) Discrete power MOSFET (with body diode) ~ fixed drain and source

(a) When Vdd is applied to the drain:
Vgs = H (NMOS 'ON') => Vs = a little bit less than Vdd (very small ON resistance)with current flowing from the drain the source (body diode 'OFF')
Vgs = L (NMOS 'OFF') => source terminal is floating with no current (body diode 'OFF')

(b) When Vdd is applied to the source:
Vgs = H (NMOS 'ON') => Vd = a little bit less than Vdd (very small ON resistance)with current flowing from the source to the drain (body diode 'OFF')
Vgs = L (NMOS 'OFF') => Vd = Vdd - Vdiode (body diode 'ON') with current flowing from the source to the drain

Hope it won't confuse you ~

Will :D
 

JoseLeonardo

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Ok, in the case when the transistor is integrated, the current can flow in a direction. The direction is Drain to Source. When a transistor is integrated you can´t chance the terminals, each terminal have thier functions predefine by designer.
 

integrator

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inverter said:
The drain terminal is connected a positive voltage source through an inductor, and the source terminal is connected to zero potential. when the mosfet is still on, the current flows through source to drain. Is this current flow through body diode or its channel.
\]

When the transistor is on, and the source is at a lower potentail than the drain the curent flows from drain to source through the channel. If the body contact is at the same potential as the source this is the only thing that's happening.

However, if the body is at a lower potential than the source (and it must be if it is not at the same potential) the threshold voltage (Vtn) will increase....in a small signal model this is modelled as additional drain current, that is dependent on the potential differnece between the body and the source.

The current always flows in the channel.

hope that answers your qustions. Otherwise refer to Sedra and Smith or Razavi's books for more details.
 

raybo

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when saturated and that is the QESTION can current flow both direction the answer is yes the same apply to trnsistors also. of course there are some non linearity
 

Santoshalagawadi

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except transistor mosfet is a unidirectional device
the current always flow from source to drain
 

parthiv2eng

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Simply saying...MOSFET is bidirectional. Current flow from Higher potential to Lower. It's not necessary source to drain.
 

syeda amna

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[/QUOTE]can the current of N-chanel MOSFET flow through source to drain(not from its body diode) when the MOsfet is turned on?

Thanks! [/QUOTE]

yes it can because any terminal can b serve as source or drain. MOS is a symmetrical device.
 

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