On Fri, 4 Feb 2000 23:46:55 +1100 "Paul B. Webster VK2BZC" writes: > > > > When the FET is opened, the coil current will ramp down, through > the > > inductor. I think it's important that the FET be off long enough > to > > allow the current to ramp all the way down. > > Sorry, that's the very thing you want it *not* to do. > My concern here is that without some sort of feedback, this "continuous mode" switching will drift one way or another, possibly having the coil current increase a bit more each time the FET is on. I agree that a small current variation in continuous mode would make the solenoid quieter, but can you do this without feedback? How about feedback of a current sense (either a small resistor in the source lead or use of a SenseFET) so that when the current goes above some level the FET is turned off, below some level it's turned back on? No duty cycle calculations required... and the hysteresis would determine the switching frequency. Harold ________________________________________________________________ YOU'RE PAYING TOO MUCH FOR THE INTERNET! Juno now offers FREE Internet Access! Try it today - there's no risk! For your FREE software, visit: http://dl.www.juno.com/get/tagj.