Post by thread:[EE] Multiple Emitter Transistors

Hey, all. This is my first post in a couple years, so be nice to me ;) I've been looking at the schematic of a TTL NAND gate, and the use of multiple-emitter bipolar transistors throughout the 74xx TTL family of devices -- From my googling, I have founds posts that multiple emitter transistors were once manufactured as discrete components back in the 70s, but they are apparently no longer available. So, my questions -- are multiple emitter transistors available as discrete components? If not, is there a way to simulate the operation of a multiple emitter transistor with discrete components. I have read that the input transistor on a TTL gate, (where the multiple emitter transistor is used) can essentially be substituted with diodes, as the transistor only acts as a simplification of multiple steering diodes -- is this true? Thanks, Keelan ____________________________________________

Keelan Lightfoot wrote: > So, my questions -- are multiple emitter transistors available as > discrete components? Not that I know of. > If not, is there a way to simulate the operation > of a multiple emitter transistor with discrete components. Multiple transistors with the collectors and bases ganged together. > I have read > that the input transistor on a TTL gate, (where the multiple emitter > transistor is used) can essentially be substituted with diodes, as the > transistor only acts as a simplification of multiple steering diodes > -- is this true? You could use one transistor with a diode for each separate "emitter", but this would have higher effective Vbe voltage drop and a little slower turn off time. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com ____________________________________________

Olin, > Multiple transistors with the collectors and bases ganged together. I had suspected this might be the case, and I suppose I could have just tried it! Thanks for the help. Keelan ____________________________________________