[time-nuts] Power supply for Thunderbolt

David C. Partridge david.partridge at dsl.pipex.com
Mon Apr 21 04:40:51 EDT 2008

I'm in the process of buying a Thunderbolt, and will need to provide it with
some volts.

I sat down over the weekend to design a linear supply for it.  Initially
things looked OK using a 12-0-12 transformer, and a few IC voltage
regulators, but then I did some worst case design and dissipation analysis,
and found that I needed to use a 15-0-15 transformer to allow for a -10%
mains variation, and add pass transistors and lots of heat sinking to all
the regulators to allow for a +10% mains variation.

Add to that transformer regulation issues (over-size transformer), the time
to design the PCB and the cost of getting it made, and things started to
look expensive :-(.

I can probably source a linear supply on eBay, but these are typically
pretty large and heavy.  For example: eBay item number 330201077319

So is it reasonable to use an SMPS, and add additional filtering to the
output?  Typically these talk in terms on 150mV ripple & noise which I need
to reduce by a factor of ten or better. 

If you have been there, done that, I'd be interested to hear what you did.

Dave Partridge

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