On 3/9/19 7:42 PM, Gerhard Hoffmann wrote:
Am 10.03.19 um 01:38 schrieb jimlux:
Has anyone tried a +5V to +15V DC/DC to run an OCXO, getting the 5V
from one of those rechargeable USB power bricks. I was thinking about
portable operation.
In my case, the OCXO is something like a Wenzel streamline. I would
think that the DC/DC probably has some noise, but maybe DC/DC to a
higher voltage, then a good linear regulator to clean it up (or would
the radiated noise just leak around).
How quiet is the output from those USB battery things..I've used one
to run a RTL-SDR, but that's hardly a ultimate low noise receiver.
That's impossible to predict. These boxes normally contain one Lithium
cell and a DC/DC converter to 5V.
Its output noise depends on the skill of the designer and the mood of
the bean counter. It is probably
not a high priority. Also, there my be "effects" from the interaction of
their switcher and your's.
And the efficiencies multiply.
BUT:
3 of these Li cells deliver 12V in ultimate quality:
True.. but there are a plethora of the USB 5V power blocks around - in
general, there are lots of USB 5V (noisy, I'm sure), e.g. Cars now have
5V USB jacks, so I was thinking about designing with that in mind.
The question is really more one of "how much filtering do I need to
design into the downstream power supply circuits"
<
https://www.flickr.com/photos/137684711@N07/39972841815/in/album-72157662535945536/
>
The squares on the paper are 5mm.
Noise density is better than 1nV / rtHz above 100 Hz. You definitely
need a fuse. Ishort is >> 30A.
Oh ho.. yes, as long as you stay with cylindrical cells.. if you go to
pouch cells, they can catch fire internally with no load needing to be
attached. We had a bit of excitement on lab a couple summers ago,
luridly captured in this nice headline from the Daily Mail
"Nasa reveals shocking video of secretive military 'RoboSimian'
EXPLODING as its batteries catch fire" (I *am* disappointed that they
didn't work aliens into it somehow)
Or from everyone's favorite, RT: "Shocking video shows NASA military
robot exploding due to battery failure"
https://media.wired.com/photos/5926a837cfe0d93c47430f84/master/w_582,c_limit/robot-explosion.gif
This Panasonic type is OK. There are lots of others on the market that
claim twice the power capacity
but it's a blatant lie.
for all practical purposes any legitimate 18650 sized Li-ion cell is
around 3.5 Ah.
regards, Gerhard
(who thinks about using a dozen of these for portable EME tests on 432
:-) )
You're going to run your kilowatt amp off 36 cells in series? Why not..
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