Re: Can I use one base resistor for several transistors?


Jon Danniken wrote:
Hello,

I am needing to drive four transistors (NPN, NTE123, 2N2222, etc), which are
being used as switches for fairly equivalent loads, from the output of a
4013 flip-flop.

Is there any reason not to just use one base resistor for all four
transistors, or am I missing something really obvious?

Thanks for any insight into this,

Jon

You can't. Unless the transistors' base-emitter voltages are matched
(which they won't be), one transistor may hog all the drive current,
leaving the other transistors wanting.

For a very light load and relatively heavy drive (e.g. i.drive >
i.load) you might get away with it, but there's scarcely any reason to
try: resistors are cheap. But, you don't have that--you're using
4000-series CMOS.

HTH,
James Arthur

.

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