Re: Confused about enhancement mode MOSFET basics

On 2 Nov 2006 06:13:31 -0800, "Ge0rge Marutz"
<gerbermultit00l@xxxxxxxxx> wrote:

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

.

Relevant Pages

  • Confused about enhancement mode MOSFET basics
    ... Every example I have seen for N channel MOSFETS assumes current flows ... from drain to source when gate voltage is positive relative to the ... Can current flow from source to drain IF the gate is still positive ...
    (sci.electronics.basics)
  • Re: rectifier
    ... >> drain on an n-channel device. ... and hopefully not conducting significantly. ... >could use a mosfet with its gate not energized, ... >as a diode with low voltage drop, acting, rather, like a resistor. ...
    (sci.electronics.design)
  • Re: will this work?
    ... drain tries to swing any more than a few tenths of a volt negative. ... So a MOSFET should be fine for switching DC if the voltage is positive then? ... This puts a second body diode in series with the first that prevents either from conducting when the gate is low. ...
    (sci.electronics.basics)
  • Re: Sync FETs; No Data Sheet Info About Reverse Operation
    ... It's probably better to simply say Rds is dominated by Vgs. ... at currents half the pulse maximum), even with high gate voltage. ... occurs after the Vds voltage drop has exceeded several volts. ... reaches a diode drop, the FET's intrinsic substrate diode is turned ...
    (sci.electronics.design)
  • Re: PMOS device reversed
    ... > upside-down..ie current flows from drain to source instead of source to ... Keep in mind, if the reverse ... ON voltage exceeds a diode drop, ...
    (sci.electronics.design)