On Tue, 9 Jun 1998 21:48:05 +0200 Morgan Olsson writes: >< curious, maybe someone here on the list have a clue > >There are schottky transistors in some logic chips: LSTTL etc. > >But why don=B4t we see discrete schottky transistors?? There is no such thing as a "schottky transistor." The "schottky transistor" used in LSTTL chips is a combination of a regular transistor and a schottky diode. The diode is connected to draw current away from the base of the transistor as the collector voltage approaches the emitter voltage. For an NPN transistor, the cathode of the diode is connected to the collector and the anode to the base. This regulates the drive to the transistor so it doesn't go into full saturation. Since the diode conducts with less than Vbe, it conducts when the collector voltage reaches about 0.3V. Any excessive drive current flows through the diode, preventing the base voltage from rising, and the transistor doesn't saturate. A fully saturated transistor takes a relatively long time to turn off, so preventing saturation speeds up the operation of a logic circuit. The properties of a "schottky transistor" are similar to those of an ordinary one except as saturation is approached. The base-emitter voltage required to turn it on is the same. It would be kind of an interesting device to have in discrete form, though you could build one yourself from a transistor and a Schottky diode. Note that schottky diodes don't like heat either, becoming even more leaky than usual. _____________________________________________________________________ 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 Or call Juno at (800) 654-JUNO [654-5866]