From: Peter Richard (prichard@microcure.com)
Date: 04/07/00-02:44:52 PM Z
Most switchers operate in the 80-400 kHz range and so are filtered to
stable DC using small caps. If the switcher is any good at all the
filtering is "robust" not "delicate". A well design logic board would
include large caps at the power source (output of onboard switcher) to
handle long (mSeconds) dropouts. Power supply noise is mostly generated by
switching transients in the onboard chips, this handled by adding plenty of
bypass capacitors placed across the Vcc and Gnd as close as possible to the
noisy components. If the designer of the Iopener did a decent job, you
really should not have to worry about any reasonably stable power source
used instead of the onboard switcher.
At 11:17 AM 4/7/00 -0700, you wrote:
>I for one wouldn't want to bypass the switchers that they have
>onboard. There is delicate filtering in those supplies to avoid transients
>associated with the high speed digital switching. That is probably why
>they had a separate power supply for the main unit. I doubt you can
>sufficiently filter if you do a 12V to 5 and 3.3 espeically if you have
>more than a couple of inches of cord between the supply and I-Opener.
>
>At 10:49 AM 4/6/00 -0400, you wrote:
>>Seems everyone looks at the power supply problem from the wrong
>>perspective. Everyone wants to condition the voltage to the input
>>requirements of the onboard switcher (which is at best, probably 80%
>>efficient). Bypass it instead, all you then need is the lower 5V and 3.3V
>>(or whatever the original outputs are) and you save the extra conversion
>>losses imposed by the onboard PS.
>>Peter
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