Curt, yes in a power MOSFET the body diode is a consequence of construction. Further it isn't really a diode, it is an SCR that can be triggered by excess dv/dt. Triggering that SCR can spell death for a half or full bridge. In a four quadrant application, it is common practice to insert a series Schottky diode between a power MOSFET and the reactive load, and to shunt that combination with a high speed or Schottky diode. As someone mentioned, International Rectifier offers a wealth of valuable information on power MOSFETs, as does Intersil, and Vishay/Siliconix. Steve At 09:19 AM 4/27/2005 -0500, Curt McNamara wrote: >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 >This message (including any attachments) contains confidential >information intended for a specific individual and purpose, and is >protected by law. If you are not the intended recipient, you should >delete this message and are hereby notified that any disclosure, >copying, or distribution of this message, or the taking of any action >based on it, is strictly prohibited. > > > >-----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 >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >List FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > >List technical documents are available at: > http://www.si-list.org > >List archives are viewable at: =3D20 > //www.freelists.org/archives/si-list >or at our remote archives: > http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > =3D20 >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >List FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > >List technical documents are available at: > http://www.si-list.org > >List archives are viewable at: =20 > //www.freelists.org/archives/si-list >or at our remote archives: > http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > =20 > >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >List FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > >List technical documents are available at: > http://www.si-list.org > >List archives are viewable at: > //www.freelists.org/archives/si-list >or at our remote archives: > http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu