At 08:38 PM 3/16/2004, Russell McMahon wrote:

>Zener:
>
>Overall cct draws constant power. The more in the load, the less wasted in
>the zener.
>Highest energy drain.
>Regulation knee "soft".
>Low cost.
>Compact.
>Poor output regulation with temperature, load and Vin changes.
>Usually limited to lower power use.

Also add in: inherently resistant to transients.

Zener supplies are definitely not for everyone.  As was mentioned by
someone else, you really need to look at all aspects of supply and load
variation.  But they work well for my low cost applications: 5V rail
current is usually less than 10 mA and any analog stuff is done
ratiometrically.   Supply voltage is known and power ratings for both the
zener and resistor are oversized by a healthy margin.

All my high volume stuff runs from 24 Vac and 7805 regulators simply are
not suitable - the unregulated supply can exceed 40Vdc in rural areas with
high line voltages.  And I keep harping on the transient spike resistance:
those same rural installations see some NASTY transients when lightning
strikes even several miles distant.

dwayne

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Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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