Subject: Re: serial port control
To: Wolfgang Rupprecht <>
From: Ted Lemon <>
List: current-users
Date: 02/12/1998 14:28:48
> I was talking about a 60hz UPS, and the assumption is that the person
> designing the UPS isn't a total dork and is limiting the rise time to
> something reasonable.  Further I assumed that they did a good job and
> didn't have horrible overshoot and ringing problems.  In short I'm
> assuming that they didn't use the excuse of square wave output to hide
> all sort of sins.

This is probably not a good assumption.   The watchword with the
square-wave-output UPS is typically "cheap, cheap, cheap!".

Thanks for the explanation of switching power supplies, BTW - I had
always wondered how they work.   Two of my machines downstairs use
switching supplies; the other uses a linear supply, so I'm in a
slightly different situation than the average user.   Also, I don't
think CRTs use switching supplies, do they?

Is it possible that a typical (cheap!) switching supply makes
assumptions about its supply that aren't valid if the supply produces
a square wave, and that this could cause the linear supply to behave
badly even though an ideal linear supply might love a square-wave
input?  The reason I ask is that I have definitely heard of switching
supplies being fried by square-wave UPS's.  Could be Urban Legend, I