[Fwd: [Gb-ccb] Power supplies for CCB]

[Bob Simon]

Hi Rich,
      Sounds OK to me.  Also, you might look at Acopian power supplies. 
  They have tightly regulated linear 8V supplies available, see #A8MT500.
bob..


Richard Lacasse wrote:

> Galen, Roger, Bob,
> 
> The CCB group has changed its thinking on power supply mounting.  This 
> was triggered by the calculated, large IR drop in the original scheme.  
> I've discussed this new scheme verbally with Galen and Randy who, off 
> the top of their heads, see no problem.  Could all of you give this some 
> thought today and let me know if you see any problems.  The original 
> message is appended below.
> 
> Thanks,
> Rich
> 
> -------- Original Message --------
> Subject: [Gb-ccb] Power supplies for CCB
> Date: Mon, 10 Oct 2005 16:55:07 -0400
> From: Richard Lacasse <rlacasse at nrao.edu>
> Organization: National Radio Astronomy Observatory
> To: CCB <gb-ccb at donar.cv.nrao.edu>
> 
> Randy, Jason, et al.,
> 
> I've done a bit more thinking about power supplies for the CCB.  I'd like
> to run my thoughts by all of you and get whatever feedback you deem
> appropriate.
> 
> I think what would work best would be a system of two supplies and a
> regulator mounted on a bracket just below the CCB.  The two supplies would
> include a Power One HN5-9/OVPA (5 volts at 9 amps and 6.6 lbs) and an
> HC12-3.4-A (12 volts at 3.4 Amps and 4.25 lbs).  The regulator would be
> built around an LM338 5A linear regulator and would provide 8 volts at 2
> amps to the linear circuitry.
> 
> The following considerations drive me to this configuration electrically.
> The embedded computer is quite sensitive to the power supply level.  Having
> the 5-volt supply mounted very close by, with short wires will minimize the
> IR drop.  It eliminates the need for remote sensing.  With regards to the
> 8-volt supply, since it is not an industry standard voltage, we seem to
> have a choice between using an adjustable lab supply or adding a regulator
> to an existing supply.  Post-regulating the 12-volt supply down to 8 volts
> does not seem too unreasonable except for the wasted power, but hey this is
> analog!  One concern is the isolation of the analog supply from any noise
> generated by the fan.  We should look at this.  One thing that goes in our
> favor is the isolation gained from two regulators, one in the power supply
> chassis which regulates 12 volts down to 8 and a second in the CCB chassis
> which regulates 8 volts down to 5.  Another advantage of this approach is
> RFI.  We have used Power-One supplies in the past with no problems I am
> aware of.  If we were to buy an adjustable lab supply the RFI qualification
> could be a problem (not to mention extra weight).
> 
> There are some mechanical considerations we need to think through.  A power
> supply chassis like I'm proposing about would add about 15 pounds to the
> receiver package.  Does this have any negative consequences, e.g. pointing?
>  I don't think it makes a whole lot of difference to the moment generated
> by the supply weight, as compared to the traditional power supply plates.
> The supplies are mounted at about the same radius either way.  We would
> need to come up with an additional bracket to support the supplies below
> the CCB.  I don't think this would be very hard.  Access to the supplies
> would be a little better with them mounted below the CCB.  Installation
> would be easier.
> 
> Clearly, we need to get some decisions made fairly soon.  These supplies
> are not that expensive.  The 5-volt/9 amp for instance is $78 in stock at
> Digikey.  My feeling is that we ought to just go ahead and buy the
> supplies, design and build the bracket and give it a try.  If we have to
> backtrack, it will not have cost us very much.  What does everybody else 
> think?
> 
> Rich
> 
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