On Wed, Sep 22, 2010 at 9:26 PM, Jon Elson <el...@pico-systems.com> wrote:
> Don Stanley wrote:
> > It had not entered my mind to power the USC from the computer 12Volts.
> > The old "keep the noise out of the computer" mind set. But the printer
> cable
> > has already piped the USC ground into the motherboard.
> > If the USC input filter capacitor is able to swamp any noise from the
> > USC Isolated power chopper (on the new boards) that will work well
> > on my boards also. If it does not, a high frequency cap across the USC
> > power input will.
> >
> The 12 V in a computer is incredibly noisy, as it powers the spindle
> motors and head
> arms of the hard drives. If you put a scope or voltmeter on it, you'd
> be amazed, it will
> jump between 11.0 and 12.5 V when there is disk drive activity.
>
> There is a large MLC cap right at the switching regulator input and a
> large aluminum electrolytic right at the power input terminals.
> I think you have nothing to worry about. The isolating DC-DC converter
> has always been there, the new switching regulator
> is not of the isolated type.
>
> Jon
>
OK, thanks Jon. Now my Wall warts con go back to the devices they
were stolen from.
Don
>
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