[Elecraft] OT: Quiet 12V-to-5V converter

[Jack Smith]

There are quite a few simple switching regulator chips for 12V --> 5V, 
requiring only a handful of parts to make a complete switching 
converter. For example, National Semiconductor (now TI after the recent 
purchase) LM2591HVT-5.0/NOPB. Stocked by Mouser and DigiKey at about $6. 
This series is available in a through hole 4-pin TO-220 style device so 
breadboarding up a one-off power supply isn't too difficult.

With careful attention to detail, bypassing and shielding it should be 
possible to build a quiet 5V, 1A supply around these parts. It can be 
small enough to fit into a 2"x2"x1" Hammond die cast enclosure, and you 
can use feedthrough caps for input and output, along with some internal 
LC filtering.

Still, 5V at 700 mA with a switching regulator and a 12V battery 
(assuming 100% efficiency which isn't possible of course) the setup will 
require 300mA from the battery. For 100 hours of operation, you're 
looking at a 30 Ah battery requirement. While a battery will output more 
Ah with a 100 hour discharge cycle, it's not that much more.  A 35Ah 
sealed 12V gel-cel type lead acid battery will run you about $100.

For serious long duration battery operation, I would look for a more 
thrifty data logger.

Jack K8ZOA


On 1/6/2012 10:10 AM, John Gibson wrote:
> Dear Elecraft list members,
>
> The recent thread on noisy switching power supplies leads me to a related question. My son n8fyk, who teaches radio astronomy, has set up a project with his students. They are using a 15m direct-conversion Radio Jove receiver in the field to monitor radio emissions from Jupiter, the sun, and the galaxy. The receiver operates from 12V, which is readily supplied by a portable utility 12V battery pack. Their problem is powering their data recorder, which needs about 5V at 0.7A.
>
> The data recorder is designed to operate from three internal AA alkaline cells, but these give a limited run time. My son would like to be able to leave the receiver and recorder for unattended operation for several days at a time.
>
> One solution would be to use a 12V-to-5V power converter between the 12V battery and the data recorder. For long battery life, it would be nice to have the efficiency of a switching converter. Such a converter would have to be RF-quiet, so as not to interfere with their weak-signal reception.
>
> I will be interested to hear what list members recommend.
>
> Thank you and 73,
>
> John, no8v
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