Joe,
With the tradition rectifier/filter power is only drawn on both side of
the peak of the sine of line voltage, sort of like this:
--- ---
-----| |----------| |--------
because the rectifier diodes only conduct when Vsupply > Vcapacitor
With a switching converter, using an inductor as an intermediate energy
storage element, it is possible to draw current over more of the cycle.
This is called PFC, but is not PFC in the true sense, which is only
defined for sines.
-John
==================
> Although off-topic here, the PFC (or power factor correction) is a
> switching mode front-end used to correct the cos-phi of the otherwise
> capacitive load that every switching mode power supply is for the
> mains.
>
> On Sat, Jun 15, 2013 at 11:52 PM, J. L. Trantham <jlt...@att.net> wrote:
>> Sorry for the interruption but what is 'PFC'?
>>
>> Thanks.
>>
>> Joe
>>
>> -----Original Message-----
>> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
>> Behalf Of Poul-Henning Kamp
>> Sent: Saturday, June 15, 2013 4:09 PM
>> To: Robert Atkinson; Discussion of precise time and frequency
>> measurement
>> Cc: Perry Sandeen
>> Subject: Re: [time-nuts] HP and other equipment failure
>>
>> In message <1371329221.83869.yahoomail...@web171902.mail.ir2.yahoo.com>,
>> Robert Atkinson writes:
>>
>>> While I agree with everything else you say, you CAN have too much
>>> filter capacitance. At least where dc rectifier / filter (smoothing)
>>> circuits are concerned. Increasing C causes increased ripple current
>>> [...]
>>
>> And ripple current can be a major source of power-line frequency noise
>> in
>> all electronics.
>>
>> The main reason why switchmode power-supplies today (can) outperform
>> linear
>> power supplies with respect to noise, is because the legally mandated
>> PFC
>> correction eliminates the bridge-rectifier ripple harmonics.
>>
>> I would not hessitate to use a good quality switchmode to replace the
>> linear
>> supply in a HP5370B.
>>
>> I did some experiments a couple of years ago, with an audio-amplifier:
>> I put a standard PFC corrector chip on the secondary side of the trafo.
>>
>> The overall result was not satisfactory, but the 50 Hz "sneer"
>> we all know and hate was absent, and the "Tzoing!!!!!" power-on
>> mechanical
>> shock from the trafo was also eliminated, as was the consequent dimming
>> of
>> the lights ;-)
>>
>> The main reason not to do this, is that you need some physically
>> gargantuan
>> coils for a 10A+ PFC-switcher.
>>
>>
>> --
>> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
>> p...@freebsd.org | TCP/IP since RFC 956
>> FreeBSD committer | BSD since 4.3-tahoe
>> Never attribute to malice what can adequately be explained by
>> incompetence.
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