Re: gEDA-user: Dropping a few volts

[John Griessen <john@xxxxxxxxxxxxxx>]

DJ Delorie wrote:
> What about a BJT emitter follower with a 5v zener C-B and resistor to
> ground?  Shouldn't that give you a constant voltage drop (letting you
> optimize the transistor selection) without the drawbacks of a plain
> series zener?
> 
> 
> ------+--------       ------------------
>       |        \    _/
>       |         \   /|
>      ___/    ------------
>     / ^           |
>      /_\          |
>       |           |
>       +-----------+
>                   |
>                   \
>                   /
>                  /
>                  \
>                   |
>                   |
>                  ---
>                  \ /
>                   v
> 

Yes, where the load is on the emitter.  You could also use one of those FETs.
I"d rather see the zener to common with a resistor above it drawing some reasonable current
to give a less able to oscillate voltage to the base or gate...

John Griessen

-- 
Ecosensory   Austin TX
tinyOS devel on:  ubuntu Linux;   tinyOS v2.0.2;   telosb ecosens1


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