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'[EE] Multiple Emitter Transistors'
2004\11\22@161946 by Keelan Lightfoot

picon face
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
____________________________________________

2004\11\22@171512 by olin_piclist

face picon face
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.


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____________________________________________

2004\11\22@232908 by Keelan Lightfoot

picon face
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
____________________________________________

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