Right now, my problem is where to strike a reasonable yet good compromise.
I thought of using DC/DC but these are quite noisy, and noise comes from both
ends. I had one powering distribution amplifiers. For an experiment, I placed
a ferrite bead on the output and the whole thing oscillated rail to rail. (and
killed the dist.amp) Also, these things switch at very high speed where
ability of 3 terminal regulators to reduce noise is at minimum.
On the other hand, I was playing with red label T-bolt. This thing has
internal DC/DC converters to take 24V and turn it into +/- 12V and 5V.
Powering it with clean linear supply and a garden variety switcher, output was
equally clean. (at least far below my lab's ability to observe issues) I saw
no difference in output at all. Tech support at SRS demanded I use linear
supply for PRS-10, and declined to discuss further. Yet, I've seen most DIY
implementation uses switcher. I *think* /tvb uses 48V common supply. I also
read a comment on this list, when one is dealing with time-nut level accuracy
and stability, every milli-volt counts.
I guess I'll have to deal with this on case-by-case basis. (pun intended)
---------------------------------------
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
On Saturday, February 8, 2020, 9:11:13 AM EST, jimlux
<[email protected]> wrote:
On 2/7/20 7:01 PM, Taka Kamiya via time-nuts wrote:
> I recall S-100 scheme had an issue of per-board regulator failing short and
> dumping 8V into bus killing rest of the system....
More like the 5V regulator (most likely a trusty 7805 in a TO-3 package)
shorting, applying 8V to all those TTL parts on the board, which die,
and put 8V on the address and data lines. However, I'm not sure that
was a particularly common failure. In many years of working with a lot
of S100 systems, I never had that problem.
> I am thinking of making use of 28V (aircraft power supply?) regulated power
> supply, and have local linear regulator to created needed voltages. One
> concern is, should I need large amount of 5V then loss will be tremendous.
Probably a better solution is multiple bulk supplies off line AC then
regulate down. Or a DC/DC from 28V to 8V, then good linear regulator to 5V.
There's really no way around it, although you can do things like
synchronize all your PWM converters, so if you do get spurs, they're in
consistent places.
I just came across an article that discussed magnetic field
sensitivity of LPRO-101. The author ended up relocating the transformer
off-board. (in a different case) A very timely information as this is
what I am actually working on.
> Further comment will be appreciatedTakaTime-nut in training
> ---------------------------------------
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
>
>
> On Thursday, February 6, 2020, 6:51:38 PM EST, jimlux
><[email protected]> wrote:
>
> On 2/6/20 3:14 PM, Will Kimber wrote:
>> Hi,
>>
>> Usual (best?) is supply slight over voltage and use LDO/RC filtering in
>> each unit as Bob suggested. But that would require either supplying
>> 24v/12v/5v/-12v (with some margin 10%?) or converting some single supply
>> of 24v or 48v in each unit to required voltages at each piece of
>> equipment. The later requires switching supplies to get all voltages.
>
>
> Well that was the strategy used on S-100 boards. Bulk 8V unregulated
> supply regulated down to 5V on the board.
>
>
>
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