[hpsdr] [Fwd: Re: Tiny Demeter]

[Jeroen Bastemeijer]

Dear Mike,

Thank you for your comments. I think, I read most articles you are 
referring to. Currently I'm looking into so called multiphase DC/DC 
(buck) converters.
These converters consist of multiple smaller DC-DC converters in 
parallel. The phase relation between the different converters is well 
controlled. These converters have some advantages:
* they can be used with smaller filters, the effective current ripple is 
at a higher frequency
* faster reaction to transients in the current
* the switchers can be used closer to their 50% duty-cycle

Main question at this moment is the maximum noise the HPSDR system can 
handle on its power supply lines. I hope Phil (or someone else with a 
Mercury board) will come up with a number one of these days.

73 Jeroen PE1RGE

Mike Monett schreef:
>   Hi Jeroen,
>
>   I just joined the mailing list and was starting to read the archives
>   when I  came across this thread concerning the noise  from switching
>   supplies. I don't know how to post to an existing thread yet, so I'm
>   taking the liberty of mailing you directly. I hope you don't mind.
>
>   Switching noise  can be a difficult problem when you  are  trying to
>   get the  best performance on weak signals.  Shielding  and filtering
>   seems to  give  best  results at  the  beginning,  but  then further
>   improvement is very difficult.
>
>   One trick is to reduce the energy of the switching transient  at the
>   source by  reducing  the  slew  rate  of  current  through  the pass
>   element. Jim  Williams at Linear Technology has several  articles on
>   designing very low noise switching regulators using this technique.
>
>   For example, the LT1534 ultralow noise switching regulator  uses two
>   external resistors  to control the slew rate of the  current through
>   the pass  element.  You  can   trade  a  small  amount  of regulator
>   efficiency to optimize the amount of noise reduction needed.
>
>   Jim wrote several articles including one titled "Switching-regulator
>   design lowers  noise  to 100 uV", that appeared in  the  December 4,
>   1997 issue of EDN:
>
>   http://www.edn.com/archives/1997/120497/25df_03.htm
>
>   Other methods  change the feedback loop to reduce the  ripple voltge
>   swing on  the regulator output capacitor. There are  other  notes in
>   the Linear  Technology  Newsletter  and  Application  Notes  on this
>   topic, including a design for a switching regulator to  generate the
>   voltage needed  for the bias in a varactor vco. I could dig  them up
>   if this interests you.
>
>   Once the  switching regulator is optimized, there are other  ways of
>   generating low  dropout  regulators   that  provide  excellent noise
>   reduction. This  would  minimize the power loss  and  resulting heat
>   generated that would have to be dissipated somehow.
>
>   I hope this reaches you OK.
>
>   Best Regards,
>
>   Mike Monett
>
>
>   

-- 
Ing. Jeroen Bastemeijer

Delft University of Technology
Department of Electrical Engineering
Electronic Instrumentation Laboratory
Mekelweg 4, Room 13.090
2628 CD Delft
The Netherlands

Phone: +31.15.27.86542
Fax: +31.15.27.85755
E-mail: J.Bastemeijer at TUDelft.nl
GPS: Lat N52.00002 Lon E4.37157 Alt 46.2m