Confused about enhancement mode MOSFET basics

[Ge0rge Marutz]

Every example I have seen for N channel MOSFETS assumes current flows
from drain to source when gate voltage is positive relative to the
source.

Can current flow from source to drain IF the gate is still positive
relative to the source?

Or, would the reverse current simply flow through the devices body
diode?

Thanks,

George

 

[John Larkin]

Every example I have seen for N channel MOSFETS assumes current flows
from drain to source when gate voltage is positive relative to the
source.

Can current flow from source to drain IF the gate is still positive
relative to the source?
Yup.


Or, would the reverse current simply flow through the devices body
diode?

Thanks,

George

With the gate positive relative to the source, the fet will look like
a real, bidirectional resistor at low s-d voltages. If the drain goes
negative more than 0.6 volts or so, the body diode will conduct in
parallel with the s-d resistance.

Fets are commonly used in this mode for things like reverse-voltage
protection between say a battery and a load. The s-d substrate diode
is used like a simple series protection diode, but then cranking in
gate voltage shunts current around the diode and reduces voltage drop,
getting closer to an ideal diode.

John

 

[Ge0rge Marutz]

Thanks John

Fets are commonly used in this mode for things like reverse-voltage
protection between say a battery and a load. The s-d substrate diode
is used like a simple series protection diode, but then cranking in
gate voltage shunts current around the diode and reduces voltage drop,
getting closer to an ideal diode.

That is EXACTLY what I intend on doing.

Ge0rge