On Sat, 9 Jan 1999 15:15:37 EST Jon Petty writes: >What's the difference between a NPN transistor and an NPN hexfet? >Under what conditions would you use a hexfet? There's no such thing as a "NPN hexfet". The polarity is designated by the terms "N-channel" or "P-channel" devices. "Hexfet" is one manufacturer's brand name. More generically they're called "power MOSFETs" or just "power FETs". Sometimes you'll see N-FET or P-FET to designate FETs of different polarities. Both types of devices have 3 terminals. The Drain, Gate, and Source terminals of a FET correspond approximately to the Collector, Base, and Emitter terminals of a bipolar. The big difference between a bipolar and a FET is that the former is current-operated and the latter is voltage-operated. Tunring a bipolar on requires about 0.7V but a continuous drive current to the base. A FET requires several volts to turn on, but requires drive current only during the transistion time to charge up the ratehr large capacitance between the gate and source. In most cases, much less drive power is required to switch a FET. But for rapid switching, the driver needs to be able to supply large surges of current. > >What's the difference between a diode and a rectifier? >Are those names used interchangeably? The name "diode" can describe any diode. Rectifiers are diodes used to convert AC power into DC. Certain diode types are optimized for rectifier use. They can pass several amps of current, however they are rather slow to turn off, limiting their usefullness at frequencies higher than 60 Hz. Fast power diodes have been developed for switching power supplies. These diodes are often based on Schottky technology. ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]