OK...swapped the drain and source...working some better, but now, even tho the voltage on the control pin is above its threshold....it won't fully fire the main voltage FET so rather than getting 48V, its only around 4V. Although it does shut off now, and turns on sorta.... >From: Colin Constant >Reply-To: pic microcontroller discussion list >To: PICLIST@MITVMA.MIT.EDU >Subject: Re: [EE:] N channel FET off resistance? >Date: Tue, 2 Mar 2004 10:58:39 -0700 > >>From: Spehro Pefhany >>>I have a circuit, that uses a voltage divider on a control pin, to turn >>>it >>>on and off. Basically if the voltage is present, and above a 1.32V >>>threshold, then the controller is activated. I want to remotly control >>>this >>>device, so I tied a N channel FET (BSS138) where the source is tied to >>>the >>>control pin, and the drain is tied to ground, and the gate has a 1K >>>pulldown >>>and then driven from a PIC. >> >>I think you've got drain and source reversed. The MOSFET will actually >>sort-of work in reverse, but the body diode is conducting and keeping >>the source voltage from going more than one diode drop above ground. > >Also, Spehro, I think I would have used a bigger pulldown, no? > >Colin > >_________________________________________________________________ >Add photos to your e-mail with MSN 8. Get 2 months FREE*. >http://join.msn.com/?page=features/photos&pgmarket=en-ca&RU=http%3a%2f%2fjoin.msn.com%2f%3fpage%3dmisc%2fspecialoffers%26pgmarket%3den-ca > >-- >http://www.piclist.com hint: PICList Posts must start with ONE topic: >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads _________________________________________________________________ Learn how to help protect your privacy and prevent fraud online at Tech Hacks & Scams. http://special.msn.com/msnbc/techsafety.armx -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads