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In Reply to: RE: Power supply design for low power PC posted by John Swenson on January 03, 2009 at 16:46:07
Just your average linear power supply.
Any good electronics textbook would have the same circuit along with the theory you need to understand how to customize it to fit your needs.
Follow Ups:
Tweekeng wrote:
> > "Any good electronics textbook would have the same circuit along with the theory you need to understand how to customize it to fit your needs."
I'm sure that textbooks give informed readers the basic theory but not all of us on this list are competent to use it. Besides, the difference between a textbook circuit that works and a practical one that works well needs theory informed by experience and an eye for detail.
I do not understand why folk feel the need to be ungracious about a useful contribution to the list. If they think the design lacks merit, they should of course say why but it is wrong to suggest that John has merely rehashed a design note.
I've looked at dozens of power supply designs over the years, many of them very good. I've seen several broadly similar to John's (as you'd expect) but none identical and certainly not in the data sheets or in this context.
I find his argument about its merits convincing and it looks easy to build. It seeks to address a significant issue with PC audio and adds support to the notion of "satellite" players that he has been plugging.
I'd like to pursue the idea of adapting cMP2 to use such a device as (a) I don't know Linux but am reluctant to make the effort to learn it right now only to find I can't get it to work with my kit and (b) I am very satisifed with cMP2 and would need some convincing that Linux alternatives are better. (Never say never and all that but also a step at a time.)
Nevertheless, the core argument for using the likes of Fit-PC is strong and John's proffered PSU design adds to it. Many thanks for the effort.
Best
Dave
Not really. This design has been carefully optimized to give very low current spikes through the diodes and transformer secondary. Most modern linear designs will just use a large cap after the diode bridge. For a 1A load that will produce somewhere between 12 to 20A current spikes depending on what capacitors you used. Even if you go with a standard PI filter out of the textbook and design it the standard way you will still get current spikes in the 3-4A range, alot better than 12-20A, but this design gives you current spikes in the 1.5A range.
I never stated that this was a new unique never seen before power supply design, just that it was a carefully optimized design targeting parameters I have found to be important for audio purposes.
John S.
Because:
1) Choke in low power supply. No, this isn't the first one to do it -- Twisted Pear Audio uses small chokes in their low power supplies, for example, and DHT filament supplies have contained chokes for many years, but it isn't exactly "average".
2) TUNED secondary snubber network which as John has mentioned in previous posts can make a measurable difference with power transformer resonances.
3) Schottkys.
4) Lower value first C after diodes.
5) Extremely low DCR
6) Tested with specific components as a SYSTEM to be low noise, etc. This is a valuable and underrated aspect, IMO. Most of us don't even have the appropriate test equipment (or free time) to check things like transformer resonances.
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