> Just for starters - I'd love to know where a 75Lxx works well vs. a zener
> vs. a switcher and what the trade-offs in cost/complexity/power are.


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.

Linear regulator.

Power drain is Pout plus some extra for regulator drop and regulator's own
current.
Better energy use than zener.
Dearer than zener at low powers.
Most precise regulation.
Low noise.
CAN oscillate in bad design.
Usually needs some "glue" parts.
Can be destroyed by abuse but many parts protected against some hazards and
dearer parts against most hazards.
Max voltage in usually about 50V for IC parts.
Mixed discrete and IC implementations can be tailored for excellent
performance.

Switcher.

Usually dearest solution. Sometimes about same as linear.
Potentially more complex design but 'cookbook" designs and highly integrated
ICs make some designs trivial.
More noise than linear.
usually worse regulation than linear (but better than zener).
Can use small filter parts (as can be very high frequency) BUT hf noise can
be a problem.
Best energy conversion efficiency (usually 70% to 90%+) except in special
cases.
Usually least compact component wise BUT lower thermal losses usually reduce
overall size due to lower heatsink sizes and smaller magnetics.
Can be destroyed in more ways than linear and can be very well protected.
Always uses glue except in VERY special cases but can be very very compact.
Only type that can step UP and/or down.

Summary.

Zener: cheap, cheerful, sloppy, compact.
Linear: More precise, dearer.
Switcher: Dearer, noisier, more complex design, better efficiency.



        RM

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu