Subject: Re: serial port control
To: None <current-users@NetBSD.ORG>
From: Greg A. Woods <>
List: current-users
Date: 02/12/1998 18:55:27
[ 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
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