[time-nuts] Power supply for Thunderbolt
Bruce Griffiths
bruce.griffiths at xtra.co.nz
Tue Aug 5 22:43:03 UTC 2008
David C. Partridge wrote:
> I'm using the Meanwell T30-B, but Tom van Baak's test on this shows a bit of
> phase noise at 1Hz offset which is a tad nasty:
>
> http://www.leapsecond.com/pages/tbolt/noise.htm
>
> I'm wondering if this can be reduced with a bit of extra de-coupling on the
> 5V supply, but haven't got round to scoping the 5V supply to see what
> happens every second (presumably as the output is sent to the serial port).
>
> Cheers
> Dave
>
>
Dave
If phase noise at 1Hz offset is a problem you will probably need a
power supply filter with cutoff frequency well below 1Hz to make any
discernable difference.
Since the an RC filter will produce a voltage drop in the 5V supply the
resistor value will have to be kept small and the capacitor value
correspondingly large (several farads).
It may be possible to stack 3 low ESR super capacitors in series
(maximum voltage rating is around 2v -2.5V those with higher ratings are
actually series connected stacks) to do this but this is a relatively
expensive proposition.
Alternatively a modified version of the Wenzel active power supply
filter could be used if a series stack of 2 low ESR supercaps were
substituted for the capacitor connected from the supply to the
transistor base. The modified circuit stabilises the transistor's
effective emitter resistance and keeps the active filter dc current low.
It may also be possible to use a variation of Wenzel's opamp augmented
active filter scheme, however the filter low frequency cutoff will have
to be well below 1Hz for it to be effective.
Bruce
More information about the Time-nuts_lists.febo.com
mailing list