Date: Mon, 20 Dec 1999 11:49:45 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Wes Peters <wes@softweyr.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Cool little 100BaseTX switch - they're coming down in price Message-ID: <199912201949.LAA16719@apollo.backplane.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> <385DDE7A.1A0ED466@softweyr.com>
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:> :"everyone" here).
:>
:> This is not true at all.
:
:Oh, and how many products have you passed through FCC/EC/Japanese environmental
:certification? None, apparently.
Four in the last 15 years. I've been involved with in-home electronic
management systems and believe me, all that shit needs FCC and UL.
:> 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
:
:Wes Peters Softweyr LLC
:wes@softweyr.com http://softweyr.com/
This is old news - modern switching power supplies (and we are talking
basically a chip, an inductor, and two big caps here) switch at 50 KHz
or higher, which makes things a whole lot easier. No 60Hz humm, no
vibration - hell, you can even run the frequency up past 100 MHz and
not hear a peep out of it. Modern switching power supply chips also
have most of the shutdown circuitry required, including temperature and
current limiting, slow-start, and other features. Add in few small caps
or perhaps a ferrite bead or two to filter out HF on the DC output and
you are all done. Whoopie.
Whoopie. The only time we've ever needed a faraday cage has been in a
cable network unit for a hotel, and the video switching channels for the
in-home unit - to protect sensitive RF circuitry from the rest of the
world.
If there is a specific reason you believe that putting a small switching
supply inside the box requires extra FCC work, I'm all ears.
-Matt
Matthew Dillon
<dillon@backplane.com>
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