Date: Mon, 20 Dec 1999 00:44:58 -0700 From: Wes Peters <wes@softweyr.com> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Cool little 100BaseTX switch - they're coming down in price Message-ID: <385DDE7A.1A0ED466@softweyr.com> References: <199912190410.UAA01049@apollo.backplane.com> <385C60FC.7613CB55@bellatlantic.net> <19991218225758.A23729@futuresouth.com> <199912190556.AAA08484@whizzo.transsys.com> <199912191943.LAA06826@apollo.backplane.com> <385D47D3.FCEE9EAB@softweyr.com> <199912192127.NAA09156@apollo.backplane.com>
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Matthew Dillon wrote:
>
> :> I really hate these switching regulated DC wall plugs. They always use
> :> cheap caps in them to save money and then don't bother adding any
> :> protection to the motherboard. I prefer AC wall plugs or unregulated DC
> :> wall plugs and then a small switching regulator on the motherboard. That
> :> way you can throw anything up to 40V into it and it will still work.
> :
> :And nearly double the cost of the item, and make it much more difficult
> :(read as "expensive") to pass FCC/EC requirements. You may prefer such
> :things, but you're not willing to pay for them. (Generic "you" meaning
> :"everyone" here).
>
> This is not true at all.
Oh, and how many products have you passed through FCC/EC/Japanese environmental
certification? None, apparently.
> First, the U.L. is handled by the wall adapter.
> Second, getting FCC certification for a small device whos U.L. is
> arleady handled by a wall adapter is *trivial*.
Right, becasue you don't have to certify the power supply, you just buy
one that's already certified. If your "unit under test" requires 12vdc
input, you can provide it with any form of 12vdc power you want. At our
test facility, the most common is a car battery 200 ft away.
The power supplies are often the hardest part to certify, and the major
reason why most networking equipment is on FCC Class B certified, rather
than Class A. For those of you who are wondering why this matters, it
means it is illegal for you to use the equipment IN YOUR HOME anywhere
in the USA if it interferes with any radio or TV reception anywhere.
> Moving the switching
> supply inside verses depending on a DC adapter does not make FCC cert.
> more difficult.
You're wrong. It nearly always requires adding some sort of faraday cage
around the power supply, and often around the entire enclosure due to the
difficulty in isolating the 60 Hz harmonics within the power supply in
small equipment. For a small, cheap hub or switch this just kills the
bill of materials. The Intel 8-port switch was already noisy enough they
had to paint the inside of the case with copper spray; an internal power
supply would have killed the product entirely due to the cost of the casing
material.
> There is an expense in the power supply verses the cheap crap you get
> in a DC regulated wall adapter - well, doh! That's why it's better!
Yup, and you'd be amazed the number of people that will buy the $99 switch
over the $139 (or even $109) switch, even if they don't know the difference
is the wall-wart. Other factors (like brand recognition) aside, that number
is vanishingly close to "all of them."
--
"Where am I, and what am I doing in this handbasket?"
Wes Peters Softweyr LLC
wes@softweyr.com http://softweyr.com/
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