Safe shut down BBB

Happy New Year

I would like my BBB to be shot down correctly via shut down or halt command if power into BBB is interrupted ( and by doing that avoid corruption of my SD card).
So, I have two supercapacitors - 10F 2.7v connected in series, what I am looking for is a dc/dc converter ( stepUp) to keep output at 5V even when voltage from capacitors is slowly dropping. I need about 6 sec for system to shut down correctly from the moment of power shortage . So up to 500 mA stepUp voltage regulator. Any idea which one to use?? Anybody worked on this kind of design??
Thanks in advance

There are some interesting and unbelievably cheap converters on eBay (i.e. $1.56 + $1 shipping!):

However, in order to force a clean shutdown you’ll need to detect loss of input power (voltage comparator circuit on a breadboard cape?), generate an interrupt to the CPU, and have a software driver force a shutdown. The shutdown process might take more time than your supercaps will supply. Might be easier to use a cheap UPS, or keep a few backup SD cards.

These converters are small, so you could put one of these on a breadboard cape with your supercaps and a voltage comparator, feed input power to the cape, and power the BBB from the cape, ignoring the 5V connector on the BBB.

This converter will accept inputs from 3V-35V. You need to set the output voltage with a trimpot.

This one produces 5V output and will work with input voltage 0.9V - 5V.

Or this one if you don’t want a USB connector for output:


I really have not researched or looked into it at all really, but It seems to me as kevind says above it would be best to buy, or even make an “inline” UPS. I had been looking at these high capacity USB charger type devices, which to me seems to be a perfect fit. But again I have no looked too deeply into it.

Also, no one says just because something like this started out being a “USB charger” that it would have to stay that way . . .