I’ve designed a prototype. I’ll provide noise and ripple measurements when I get the first boards back. I’m going to shoot for <= 35 mV P-P. If you need better than that, then it probably turns into a hybrid switching+linear system, which would be more expensive. It’s been a while since I looked, but I believe that’s what I was able to achieve with the supplies for the FE-5680A GPS discipline board.

I’ve not made any efforts along those lines to start with. For one, the input is +12 V and is simply passed through as the +12 volt output (there is a TVS and cap on the input, however). Given that the Thunderbolt that I have on loan came with what I can only guess was once a laptop power supply, I started off thinking the bar was pretty low.

If you want the hybrid approach, then adding the temperature compensation to the linear regulators would clearly be the way to go.

Nick wrote:>

It's been years since I played with Tbolts (as opposed to just using
them), but as I recall there was no possibility whatever of getting the
best results from any switching supply without at least one stage of
linear "polishing."  In fact, everything I tried with initial switching
regulation benefitted from two levels of linear polishing.  It was my
conclusion that starting with a switching supply of any sort is a bad idea.

I found that for best performance the -12v supply, which feeds the DAC,
needs to be about 1000 times better than what you are shooting for
(i.e., low tens of uVp-p).  That surprised me, because I assumed there
must be some internal regulation of the DAC supplies -- but it was what
my testing showed.

Sure, a Tbolt will work with dirtier power than that, but for real
time-nuts performance I consider an all-linear supply with an
ultra-low-noise -12v rail to be absolutely necessary.  Since that is not
very hard to provide, I see no reason to try to make do with less.

One low-cost solution is to wait for a cheap Power One HTAA-16W-A
triple-output power supply to show up on ebay, and do a very minor
modification to raise the +12v current limit (so it will handle the
first moments of a cold start without current limiting) as detailed here:

http://www.ko4bb.com/getsimple/index.php?id=download&file=06_Misc_Test_Equipment/Power_One/Power_One_HTAA-16W-A_mod_for_Thunderbolt_power_supply.pdf

That approach achieves excellent results -- close to the best you can do
-- with very little fiddling.  If one wants the very best performance,
the -12v supply can be adjusted down to -16v or so to provide the
headroom to add a ULN regulator or a capacitance multiplier.  (The Tbolt
only draws a few mA from the -12v supply, so the ULN regulator can be a
suitable op amp with no external pass transistors.)

Last time I bought them, I paid $25 for a lot of three HTAA-16W-A's.

Best regards,

Charles

Charles, do you have the schematic for the HTAA-16W-A  ?  The KO4BB mod has limited info

Tnx

Jerry
K1jos@arrl.net

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of Charles Steinmetz
Sent: Wednesday, August 31, 2016 4:49 AM
To: time-nuts@febo.com
Subject: Re: [time-nuts] Anybody want a Thunderbolt power supply?

Nick wrote:>

It's been years since I played with Tbolts (as opposed to just using them), but as I recall there was no possibility whatever of getting the best results from any switching supply without at least one stage of linear "polishing."  In fact, everything I tried with initial switching regulation benefitted from two levels of linear polishing.  It was my conclusion that starting with a switching supply of any sort is a bad idea.

I found that for best performance the -12v supply, which feeds the DAC, needs to be about 1000 times better than what you are shooting for (i.e., low tens of uVp-p).  That surprised me, because I assumed there must be some internal regulation of the DAC supplies -- but it was what my testing showed.

Sure, a Tbolt will work with dirtier power than that, but for real time-nuts performance I consider an all-linear supply with an ultra-low-noise -12v rail to be absolutely necessary.  Since that is not very hard to provide, I see no reason to try to make do with less.

One low-cost solution is to wait for a cheap Power One HTAA-16W-A triple-output power supply to show up on ebay, and do a very minor modification to raise the +12v current limit (so it will handle the first moments of a cold start without current limiting) as detailed here:

http://www.ko4bb.com/getsimple/index.php?id=download&file=06_Misc_Test_Equipment/Power_One/Power_One_HTAA-16W-A_mod_for_Thunderbolt_power_supply.pdf

That approach achieves excellent results -- close to the best you can do
-- with very little fiddling.  If one wants the very best performance, the -12v supply can be adjusted down to -16v or so to provide the headroom to add a ULN regulator or a capacitance multiplier.  (The Tbolt only draws a few mA from the -12v supply, so the ULN regulator can be a suitable op amp with no external pass transistors.)

Last time I bought them, I paid $25 for a lot of three HTAA-16W-A's.

Best regards,

Charles

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and follow the instructions there.

Ah,  these are the LM723 based linear supplies,  Lambda Coutant made
variants as did Farnell,  they're renowned as high reliability,  low noise
supplies.

There are schematics out there for the variants but they're all extremely
similar if not identical.

I think I may even have a couple of original manuals with schematics,  I
may be able to dig them out and scan if they're of interest.

On 31 Aug 2016 13:01, "Jerry O. Stern" jsternmd@att.net wrote:

Jerry wrote:

Clint wrote:

noise

extremely

I don't have a schematic for the HTAA-16W-A, but Clint is correct --
each of the three supplies is a bog-standard LM723 circuit.  I am
attaching a reverse-engineered schematic I found on the net of a
different Power One supply as an example.  I hope I've made it small
enough to get through the server without list-minder approval, in case
Tom is still away.

Best regards,

Charles

On 8/31/16 11:22 AM, Charles Steinmetz wrote:

with the venerable 2n3055 (1960s!) as the series pass device, and an
exotic TIP29 (my 1985 databook has it, but the original datasheet says
1968) to drive it..

They probably used the 1970s versions of the transistor, of course,
since the 723 didn't come out til early 70s..

Some things just keep working...
I think they've amply recovered the development cost for those parts..

I am

jim wrote:

Fairchild introduced the orginal 723 (the µA723) in 1968.  I think
National brought out the LM723 within the year, but can't swear to it.

While the schematic I posted shows a TIP29 driver transistor, that was
for a different, 3A supply.  The lower-current +/-12v supplies in the
HTAA-16W-A do without the driver, and connect the 3055 directly to the
723 output (which can source up to 150mA).  The schematic I posted also
shows foldback current limiting, which the +/-12v supplies in the
HTAA-16W-A do not have.

Best regards,

Charles