[time-nuts] Power supply for Thunderbolt
Dave Brown
tractorb at ihug.co.nz
Thu Aug 7 12:21:44 UTC 2008
----- Original Message -----
From: "Bruce Griffiths" <bruce.griffiths at xtra.co.nz>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Wednesday, August 06, 2008 10:43 AM
Subject: Re: [time-nuts] Power supply for Thunderbolt
> 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
It would be interesting to see how the 'red panel' Thunderbolts (the
packaged type that run from an included switching supply fed from 24
VDC) perform under a test regime such as that TVB used to compare
various three rail power supplies. In 'distant past' posts, maybe 18
months back, it was suggested that this supply is a particularly good
performer, but IIRC no data was supplied to support this statement.
Anyone able to oblige?
DaveB, NZ
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