[SI-LIST] Re: diode connected between source & drain - why?

My experience with the body diode (as I understand it, a by-product of
device construction) is that you *should not* depend on it to clamp
an inductive kick-back. There is simply too much energy for it to=20
dissipate, and you will destroy the FET. Use an external diode
clamp which is rated for the energy -- these should only cost a few=20
cents.

                                      Curt

Curt McNamara. P.E.=20
Senior Electrical Engineer=20
Logic Product Development=20
411 Washington Ave. N Suite 101=20
Minneapolis, MN 55401=20
Tel 612-436-5178=20
Fax 612-672-0443=20
curtm@xxxxxxxxxxx=20
www.logicpd.com=20
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Christopher.Jakubiec@xxxxxxxxxxxx
Sent: Wednesday, April 27, 2005 7:44 AM
To: roymesi@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: diode connected between source & drain - why?


Hi Roy,

When current is switching through an inductive load, a reverse EMF is
generated when the current is turned off.  This diode allows a path for
this current in this situation.  This body diode comes built into the
MOSFET for free, and is not an extra device.

A diode connected MOSFET behaves like a diode, while a standard
connected MOSFET behaves like a switch with a diode in the body.

-Chris


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Roy M.
Sent: Wednesday, April 27, 2005 9:21 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] diode connected between source & drain - why?


Hi,
Can someone explain to me why are they Transistors (mosfets), that has a
diode connected between the source and the drain? I tried to find
something on the internet, but nothing... i don't understand what's the
difference between a regular mosfet and a
diode-connected-source-drain-mosfet.
Thanks!
Roy
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