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From: dold@mitisft.Convergent.COM (Clarence Dold)
Newsgroups: comp.sys.ibm.pc
Subject: Re: What are *switching* power supplies
Message-ID: <1445@mitisft.Convergent.COM>
Date: 14 Apr 90 17:30:27 GMT
References: <1990Apr14.105752.19616@cs.dal.ca>
Organization: Convergent Technologies, San Jose, CA
Lines: 43

in article <1990Apr14.105752.19616@cs.dal.ca>, lane@cs.dal.ca (John Wright/Dr. Pat Lane) says:
> 
> What is a "switching" power supply? (ie. what makes it a "switching" type
> ass opposed to what? a non-switching power supply?)

A power supply could be as simple as a transformer, with a couple of diodes
and maybe a filter on the output.
To regulate the output, and maintain a steady voltage, a Linear Supply will
be designed so that for any load within its rating, it will be capable of
delivering more power than needed.  All of the load passes through a 
regulator, usually a large transistor, which burns off excess power, 
delivering a stable voltage to the output.  There are variables, but on
the simplest level, you could say that this power supply will always use
the same amount of line power, with some given to the target load, and
some burned off wastefully.

The switching supply monitors the output target voltage, and switches the
input AC on and off at a given frequency, so that the total power delivered
is the amount required.  In theory, we now have no regulator burning off
useless energy, we never take it in in the first place.

Plusses:  The switching regulator is more efficient at less-than-peak loads.
Minus:  It is more expensive, and dreadfully more susceptible to power
line noise.  

Linear Supplies usually have gigantic output filters, where the switching
regulator has very little filtering, since it can respond faster to a 
changing load, but the output is very noisy, intolerably so in an 
environment with poor power.

In either of them, the output voltage varies as the load varies, but they both
respond to that change in a manner that appears to result in a stable voltage.

> Why exactly is it that you're supposed to wait ~30 sec between switching
> off and on again.

Never heard that one.  I think it might be to wait for hard disks to come
to a stop, nothing to do with the supply.
-- 
---
Clarence A Dold - dold@tsmiti.Convergent.COM            (408) 435-5293
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