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Bidirectional NMOS switch??

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aryajur

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In the schematic attached below, How does the Series MOS combination act as a switch. The second MOS towards the load, will have its source a bit higher than the drain, although the Vgs is maintained sufficient, but will it conduct in the opposite direction?
This would be operating in the region of negative Vds. So the query can be put as will the MOS Id-Vd Curves be like for positive Vds just mirrored through the origin??

So now if this acts as a switch we can use it as a bidirectional switch since its symmetrical?
 

MOSFET is symmetrical. The high voltage side is Drain and lower voltage side is Source, therefore current always flows from Drain to Source.
 

A MOS is symmetrical only if it is given as a 4 terminal device. These MOS are not symmetrical since the bulk is tied to 1 terminal and and that will always be the source.
 

The MOSFET allows the current to flow in both directions when it's on. The combination used here is meant to eliminate the effect of the body diodes when the D-S voltage is reversed.

So, yes this circuit can be used as a bidirectional switch. Just make sure the control voltage is always applied between the sources and the gates, with the gates more positive than the sources.
 

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