V G wrote: > On Wed, May 25, 2011 at 4:55 PM, Forrest W Christian = wrote: >=20 >> When fully on, a FET has a resistance - RdsON. >=20 > So the gate controls the resistance? Basically, yes. >> When fully on, a Bipolar has a voltage drop - Vce(sat) >=20 > So what does the base control exactly? If the current through the > base controls the current through the collector, and I =3D V/R, is it > also controlling the resistance?=20 I is only V/R for a linear R, or within a linear region of a non-linear R. The C-E path of a bipolar transistor that is used as a switch and is "on" is not usually in a linear region, differently from a FET.=20 The Vce(sat) voltage increases with current, but not linearly, whereas the drain-source voltage of a FET that's "on" increases linearly (in first approximation) with the current. Hence the specification of an RdsON for switching FETS and Vce(sat) for switching bipolars.=20 Gerhard --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .