[hpsdr] Demeter progress

[Jeroen Bastemeijer]

Dear All,

There are a lot of thoughts around about the implementation of Demeter 
(just read all the previous E-mails). As the whole HPSDR-project is 
based on modules, Demeter should be able to adapt (alomost) to each 
individual HPSDR configuration.
A modular power supply means a power supply with certain "options" (like 
e.g. a status display or a battery charger) but also with a variable 
power. For one configuartion 5V @ 1Amp might be sufficient while another 
configuration might need 5V @ 3.5 Amps. Building a power supply with 5V 
@ 20 Amps will certainly be sufficient for all kind of 
configurations...... but I'm sure this is not the solution we are 
looking for.
To make a power supply scaleable I have been looking around on the 
internet, and giving my creative thoughts some room...

There are a few things which would fit in the Demeter concept:
1. Using a PIC for the SMPS controller (you can check the Microchip 
website for AN216) This will certainly add the High Performance to Demeter.
2. Build a multiphase controller. Just google for "multiphase SMPS" and 
you will find loads of information. This solution will give some extra 
flexibility: People who need less power, can ommit a couple of "phases" 
as one or two phases can provide enough power for their solution. People 
who need more power can extend the SMPS to four phases. As this 
technique is rather new, I hope we don't get any patent-issues when we 
apply it for the HPSDR-project.
3. Another nice technique is 'soft-switching'. This will limit the 
influence of big switching spikes.

A general question I'm trying to get an answer on is the following: How 
does the output noise spectrum (please note: not the level of noise but 
the way it is distributed through the spectrum) of  a SMPS depend on the 
load of the SMPS?

The thought on which this question is based is the following: Looking at 
the spectrum of a 50% square wave you only see odd harmonics. When the 
duty-cycle starts to differ from 50% more even harmonics start to 
appear. The regulation principle of some types of switchers depends on a 
PWM switching signal. This means that they will produce more noise at 
low loads (duty cycle < 50%), the lowest noise at half the power rating 
(duty cycle 50%) and more noise for higher power levels. If this is 
true, it would be worth to try to match the power supply as close as 
possible to the power which is required for a certain HPSDR-configuration.

That's all folks, for now at least,

73 Jeroen PE1RGE

-- 
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
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