[time-nuts] New Thunderbolts available without a power supply?
dave at uk-ar.co.uk
Thu Jul 16 12:19:31 UTC 2009
> Message: 7
> Date: Thu, 16 Jul 2009 04:42:13 -0700 (PDT)
> From: Stanley Reynolds <stanley_reynolds at yahoo.com>
> Subject: Re: [time-nuts] New Thunderbolts available without a power
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Message-ID: <382249.92561.qm at web30305.mail.mud.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
> Ok, but not very good, see :
> ----- Original Message ----
> From: "asmagal at fc.up.pt" <asmagal at fc.up.pt>
> To: time-nuts at febo.com
> Sent: Thursday, July 16, 2009 5:18:10 AM
> Subject: Re: [time-nuts] New Thunderbolts available without a
> power suppy?
> It seems to me that an ordinary PC power supply outputs +12,
> -12 and +5 Volt.
> Has someone in the list used one of those to feed the Thunderbolt?
> Thanks for reading,
> Quoting Robert Harmon <harmon52 at mchsi.com>:
> > Just wondering if the new TBolts from TAPR might be
> available WITHOUT a
> > power supply?
Applying the KISS principle...
Yes PC PSU's are noisy (most SMPS's are) especialy when "under loaded"
so the switching regulators are not working in the mode they were
designed for, resulting in their own internal filters not working
optimally for the EMI spectrum so produced. They can be relatively
quiet when correctly loaded, but to do that, you waste (a lot of)
energy, by needing loading up the "primary" output, the one with the
main feedback path to the controlling regulator. (Usually the +5V, but
not always with some of the modern stuff.)
Why not.... (Assuming a 24/7 powered PC is used...)
Fit a connector to the back panel of your PC (that will probably be used
to monitor it in any case) and then use an EMI filter, to get rid of
most of the noise Series L, Shunt C etc. You should easily be able to
better the "MeanWell" supplies noise performance, and save on hardware
I do this to run various external "attachments" from (Filtered) +5V and
+12V feeds from one of my PC's. If you look around, you can even get
panel mount versions of the 4 wire DC power connector most PC's used for
hard disks and CD ROMs. Making life even easier. Some will even fit in
redundant connector holes you may already have.
If you want a fairly quiet cheap +5V, start with the PC's 12V, and use a
good linear regulator, but remember to pay attention to it's local
decoupling, or you may remove the SMPS hash, but replace it with a 50MHz
spur on the 5V, as many 3 terminal fixed regulators will freely
oscillate if you don't get their local decoupling correct. See the
Oh, remember to fuse any supply you "borrow" from a PC. Most PC PSU's
can pack quite a punch!...
The only down side... Eggs and baskets. If the PC fails, your GPSDO
stops! But if it's just a time server with a GPS receiver for the 1PPS
signal as I use, no real long term issues.
Of course, for the ultimate in quiet supplies, it takes a lot to beat
the "old school" transformer rectifier and linear regulator approach.
Check out any collection of old "brick-in-cable" PSU's you may have
kept, after sending some early gadget to the landfill site. Many
devices used +-12 and +5V, as well as other useful voltages...
More information about the time-nuts