On Sat, 18 Jun 2011 04:06 +1200, "RussellMc"  wrote:
> >> Could you draw a simple schematic on how this "clamp" works? I'm not r=
eally
> >> understanding it.
>=20
> Cct ex TI datasheet
> TL431 December 2005.
>=20
> R1, R2 set clamp voltage.
> 431 turning on turns on transistor and clamps voltage.

How large have you made the R1/R1 combination and still gotten decent
voltage tolerance over "room" temperature range?

The input bias current is rated at 2 to 4 uA +- 0.8 to 2.5 uA over
temperature range 0 - 70.=20

Lots better than a zener but maybe would drain the battery fairly
quickly unless the R1/R2 pair was very high and then input bias current
shift eats away at accuracy.

Bob

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