> I really like the TL431. It's dirt cheap.
> The TL431 datasheet says that it needs a minimum of 1mA cathode
> current. This might mess up A/D accuracy if using a higher value
> series resistor.

> The TLV431 is more acceptable, at ~55uA cathode current. These values
> probably vary slightly depending on manufacturer.

Yes. Lower current at regulation dropout is one of the advantages I referre=
d to.

The "required" currents are what's needed to get it around the "knee"
and into proper regulation.
If it's drawing less than that it MAY be in regulation if at about the
knee voltage BUT if it's not in regulation it will be drawing less
than that.

50 uA at 5V is the equivalent of a 100k load. Current falls semi
linearly with volateg for several volts below that so looks roughly
like 100k load from say around 2 V up.

You can get a much sharper knee by adding one extra transistor
(bipolar or FET) and using the TL431 to operate that. Only load then
below clamp voltage is the sense divider.

          Russell
--=20
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