[sdiy] wall warts--wishful thinking

[John L Marshall]

Four terminal capacitors.

Take care,
John

www.sound-photo.com
47-30-39.02 N, 122-09-51.75 W, elev 440'
----- Original Message ----- 
From: "Tim Parkhurst" <tim.parkhurst at gmail.com>
To: "John Blacet" <blacet at blacet.com>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, August 16, 2005 3:03 PM
Subject: Re: [sdiy] wall warts--wishful thinking


> On 8/16/05, John Blacet <blacet at blacet.com> wrote:
>> I did some very basic external filtering work with a small switcher and
>> got nowhere! Obviously, this not trivial.
>> 
>> If anyone comes up with a decent filter or some technical info of
>> interest, let us know.
>> 
>> It would be great to get rid of heavy transformers and get more
>> efficient energy wise.
>> 
>> --
>> Regards,
>> John Blacet
>> 
>> Blacet Research
>> http://www.blacet.com
>> 
> 
> Hey John,
> 
> Have you tried the CLC "Pi filter" suggested by FMC (Fabio)? It was
> suggested in the "switched mode PSU" thread, and looks to be
> promising. I've included an excerpt below.
> 
> 
> Tim (Pi R round, the last time I looked) Servo
> -- 
> "Imagination is more important than knowledge." - Albert Einstein
> 
> *************************
> Old-fashion pi filters (C-L-C) can do miracles... don't know why they
> aren't used anymore. (cost? space?..) Try a dual pi scheme, ie:
> 
> _____C______   __L1__   _____C_____    __L2__   _____C______
> 100pF + 1nF ->  50uH -> 1nF + 0.1uF -> 150mH -> 0.1uF + 470uF
> 
> L1 can be done with some copper and one 1/2W resistor, L2 can be done
> from the secondary of a dead wall-wart trafo (choose one with an open
> primary, discard those whose primary is burnt (melt))
> 
> I've seen some designs using Rs instead Ls for the pi. This is bad.
> The inductor on the pi keeps Rsource low while having a hi_z for the ac
> content (including transients), something that doesn't happens with
> resistors. A Pi(c-r-c) and a Pi(c-l-c) are two completely diferent
> things.
> 
> Of course, a good emi shield is another completely diferent thing too.
> 
> As a side note: I always include L-C filtering in power rails of
> every pcb I make. It takes a bit more time and space (just a bit)
> but it extend noise isolation not only between the card and the PS
> but among the cards themselves. (and it doesn't hurt)
> 
> Fabio.
> ***************
>