Re: gEDA-user: Switching regulator question

[John Doty <jpd@xxxxxxxxxxxxx>]

On Jun 18, 2007, at 9:48 AM, John Griessen wrote:

> Randall Nortman wrote:
>> On Sun, Jun 17, 2007 at 08:53:37PM -0400, Dan McMahill wrote:
>> [...]
>>> Personally I avoid aluminum electrolytics like the plague.
>
>> And I'm in the unfortunate situation of designing for 70C ambient,
>> natural air convection for cooling.
>
>
> That temp means some expensive caps, so you could design for  
> minimizing
> number of high quality caps -- like a spacecraft design.  How much  
> power?
> Horsepower?
>
> Do give ceramic multilayer caps a look.  They are much more dense  
> now than ten years ago,
> and Taiwanese and Chinese and making them high quality and low cost if
> you need to plan for production.  If you design
> a low cost one layer board of CEM-1 instead of FR-4 you could use  
> up more area
> holding rows of MLC caps and have a good design.  But then you need  
> to have
> assembly of wire jumpers to make your crossovers if you only have  
> one PCB layer...
> else surface mount jumpers to make crossovers with.
>

For the spacecraft converters I mentioned earlier, I used  
polypropylene capacitors. Bulky for a given capacitance, but you can  
find parts with very high ripple and surge current capability. When  
that's what drives the design, they are less bulky than other  
approaches, and as Dan has noted the capacitance is generally enough  
if they can handle the current. I also used wet slug tantalums for  
snubber/dampers, but they had resistors in series to limit the current.

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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