[ On Thu, February 12, 1998 at 14:28:48 (-0800), Ted Lemon wrote: ]
> Subject: Re: serial port control 
>
> This is probably not a good assumption.   The watchword with the
> square-wave-output UPS is typically "cheap, cheap, cheap!".

Exactly!  You get what you pay for!  ;-)

> 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?

All of my terminals and monitors, including my old VT100's all have
switching supplies.  The only linear supply I have that I'm thinking of
still using is one that's in a really nice rack-mount chassis I hope to
build my new firewall into.

> 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
> suppose.

I've seen switching PS's that have been fried and the only explanations
possible are either that the square-wave "U"PS (they're not usually
truly un-interruptible -- though the timings are quite fast compared to
all the old-fashioned ones) caused the damage, or some really wicked
spikes got through as the power failed.  One would think though that the
spikes would have damaged the UPS too....

-- 
							Greg A. Woods

+1 416 443-1734			VE3TCP			robohack!woods
Planix, Inc. <woods@planix.com>; Secrets Of The Weird <woods@weird.com>