[time-nuts] Thunderbolt Supply

[Mark Spencer]

As mentioned before a suitably rated single transformer with a center tapped secondary will suffice if you want to build your own linear psu.  I use a 2 amp 25.2 volt center tapped transformer (along with a bridge rectifer, filter caps, 3 terminal regulators, fuse holder etc.)

I don't losse any sleep over the 5 volt regulator having to dissipate several watts more than it would if I had a differrent transformer.

On Mon Feb 14th, 2011 1:31 PM EST Larry McDavid wrote:

>I think you should look at the specifications for the noise-rejection capability of those three-terminal regulators. They are simple and inexpensive but not particularly good at noise rejection. Some of the noise from the switcher supply will pass through. Is it enough to cause a real problem? Unknown to me as yet.
>
>The power requirements of the Thunderbolt are not the usual ones you see standard supplies designed to meet. I have yet to find a small linear supply that is adequate that does not absolutely dwarf the Thunderbolt itself!
>
>Back in The Day, one could find a good assortment of multiple-secondary power transformers that would allow us to build a simple linear supply with the three-terminal regulators; there would no switcher to generate noise. Alas, these transformers are no longer easily available today. I think it can be done with two separate transformers but with the filters, regulators and actual wiring, this adds up to a lot of work!
>
>TAPR does offer a 13 vdc input, three-output power supply kit for their software-defined radio kits, but its -12 vdc output comes from a switching dc-dc inverter. That -12 vdc does supply the Thunderbolt OCXO so I have some concern about noise on that power feed.
>
>One could get a custom-designed PC board mount transformer and develop a board to supply adequate power. I doubt there is enough interest or purchase volume to justify this, however.
>
>So, I'm still looking for a compact linear power supply. I welcome your suggestions!
>
>Larry W6FUB
>
>
>On 2/14/2011 10:06 AM, EWKehren at aol.com wrote:
>> Yes I am doing it with some very low cost switchers off ebay, followed by
>> linear regulators as I mentioned previously. Works great.
>> Bert Kehren
>...
>
>-- Best wishes,
>
>Larry McDavid W6FUB
>Anaheim, CA  (20 miles southeast of Los Angeles, near Disneyland)
>
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