Date: Fri Nov 30 13:01:14 2007

Author: Bernard Cleyet

Subject: Re: Power Supplies - Switching vs. Linear

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Finally someone mentions filtering and shielding and, "... large
harmonic content"? I thought these supplies were DC output?

What gives?

If the output were intended as a 110 V. domestic supply from a solar
system I would understand that. I constructed an LC filter for a
friend's solar system. It wouldn't drive the motor in his slide
projector without it.

bc puzzled

Dan Bernoulli wrote:

> that might be affected are themselves powered by switching power
> supplies.>
>
> Its all in the engineering. Notice the shielded power cable with the
> ferrite toroid? Notice the way the equipment is enclosed in a faraday
> cage? Notice the FCC certification? The testing on these things is
> incredible. That's part of the reason one doesn't see so many
> homegrown products on the market anymore. The shielding requirements
> are really pretty tough. It takes tens of thousands of units to
> justify the design cost for most electronics instruments.
>
> As another confusing consideration, I recall many "precision" power
> supplies that had analog, i.e. linear front ends, then 40 kHz or so
> switchers for the "fine" stabilization. Some of the high end HP
> supplies from the 60(?)s worked that way. They were rock solid, could
> anchor a battleship (rhetorically speaking) and were worth their
> weight in gold (again rhetorically speaking). Its all in the
> specifications. Regardless of the topology, better supplies cost more.
>
> Were the 60s really 40 years ago?
>
> Dan Beeker

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Finally someone mentions filtering and shielding and, "... large
harmonic content"?=C2=A0=C2=A0 I thought these supplies were DC output?

What gives?

If the output were intended as a 110 V. domestic supply from a solar
system I would understand that.=C2=A0 I constructed an LC filter for a
friend's solar system.=C2=A0 It wouldn't drive the motor in his slide
projector without it.

bc puzzled

Dan Bernoulli wrote:

ng,
though, is the likely fact
that all of these nearby items that might be affected are themselves
powered by
switching power supplies.>

Its all in the engineering. Notice the shielded power cable with the
ferrite toroid? Notice the way the equipment is enclosed in a faraday
cage? Notice the FCC certification? The testing on these things is
incredible. That's part of the reason one doesn't see so many homegrown
products on the market anymore. The shielding requirements are really
pretty tough. It takes tens of thousands of units to justify the design
cost for most electronics instruments.

As another confusing consideration, I recall many "precision" power
supplies that had analog, i.e. linear front ends, then 40 kHz or so
switchers for the "fine" stabilization. Some of the high end HP
supplies from the 60(?)s worked that way. They were rock solid, could
anchor a battleship (rhetorically speaking) and were worth their weight
in gold (again rhetorically speaking). Its all in the specifications.
Regardless of the topology, better supplies cost more.

Were the 60s really 40 years ago?

Dan Beeker

cut




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