Wow - thank you!!!  I wish I could do better - but here is a (virtual) beer!
    http://beer.trash.net/beerpage.php?beernum=619

Dan

Russell McMahon wrote:

>>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
>
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>
>

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