Mitchell D. Miller wrote: > > > "Use HexFets, not bipolar transistors" > > What's special about HexFets? > > Mitch Miller, Omaha, NE > mdmiller2@home.com Several others have it right Transistors are current amplifiers, a FET is more like a voltage-controlled switch or (non-inductive) relay. I like HexFETs, just a quirk maybe The logic gated ones have really been convenient in some packages I've made in the past. With a FET instead of a bipolar, you do have to make sure you saturate the FET (the logic gated FETs handle this for you.) The advantage is that, when switching a 1A 12V load (for example), instead of dissipating base drive * base current + Vce * Ice i.e (0.7V*(1A/hFE)) + (0.3V*1A) or about 0.31 watts in that transistor, you dissipate (1A^2*0R01) or 0.01W in that FET, if you're running off a battery pack that can make a big difference. (The 1A is the real killer, of course, in this case that was just the startup surge, and you need to saturate the transistor/FET for THAT; the sensor's supply current then dropped down to about 30mA - no use dissipating 20mA into that transistor, to keep a 30mA load switched on, the HexFET made a big difference here. Net savings, about 35% of the power budget, for one project.) Mark -- I re-ship for small US & overseas businesses, world-wide. (For private individuals at cost; ask.)