I prefer switching supplies over standard pass-element regulators
because:

-- Switchers can provide a very precise DC output while the input
can be very noisy.  I am stating that in a very noisy input environment,
switchers can provide a very quiet output. For example, in automotive
systems, switchers are much less expensive that smoothing-choke
battery supply filtering systems.

--Dramatically reduced (or no) heat generated.

--Capable of enormous secondary load swings while maintaining regulation.

--Reduced need for expensive and physically large filter electrolytic caps.

Since most of my designs are automotive or battery managed, switchers
allow the designer a way to load-manage a battery system to wring out
the absolute MOST from a LiIon battery. 

Here is a good example. The design needed to get maximum battery life
from LiIon cells. The 3.8V output had to be precisely regulated over a
range of 10uA to 1A within 20mV. It had to be able to do this while the
battery cell could range from 2V to 4.2V.  We took two identical LiIon
cells in series, having a range of 4V to  8.4V, which was buckdown regulated
to 3.8V, and operated when the battery ranged from 8.4V downto 4V. In
addition, the 8.4V battery pack fit the switching charger device operating
on an automotive source ranging from 17V down to 9V. The switching
charger generated so little heat that it was mounted on the product itself.

Without switchers, none of these schemes would work.

--Bob

Marcel Duchamp wrote:

> Mauricio Jancic wrote:
>
>> Hi,
>>     I have a question. When should one consider choosing a switching
>> power supply over a standard AC/DC + CAP + Voltage regulator?
>>
>
>>     I would like to know why should I want to or consider to change to a
>> switching power supply... is it usually more expensive, right?
>
>
> 1. Where does the power come from?
> If it comes from a limited source such as a battery, you may want to 
> maximize power delivery so even when the battery drops low, a switcher 
> can boost it back up.  But if the circuit is power by AC mains, then a 
> transformer/linear regulator is often all that's needed.
>
> 2. Where does the power go?
> If a large portion goes into heating your linear voltage regulator, 
> then a switcher might make sense.
>
> 3. Do you need absolutely the lowest amount of power supply noise? 
> Switchers generally make more noise than linears. You really should 
> test this theory first with your circuits however.  I have seen plenty 
> of sensitive analog circuits run from switchers with no problems.
>
> 4. Expense?  Depends on how much power you are dealing with and how 
> you will remove heat.  In a linear supply that generates a lot of 
> heat, you may need large heat sinks, fans, etc.  These are not free of 
> course. With so many switcher chips on the market, switchers don't 
> have to be expensive.  Plus, you can make your own with stuff like the 
> PIC10F222, especially for low power designs.
>
> Good luck!



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