Jim Harrington posted:
YLB - So what's in there? Capacitors and rectifier & voltage regulator?
Quite a lot of stuff. Obviously, there's a supercap, need that to store the energy. I first use a linear regulator to charge the supercap to 5 volts. Since the supercap rated at 5.4 volts, and the RailSounds board needs around 7 volts minimum, it's obvious that I can't simply use that voltage to power the battery output directly. So, there's a second switching boost regulator to generate 8 volts for the output. There's a good reason for the two regulators. My boost regulator will continue to supply the 8 volts until the supercap discharges to around 2 volts, so I get to use a majority of the stored energy in the capacitor for power. If I assume 19 joules of energy when charged to 5V, and 3 joules of energy when charged to 2 volts, I got to use a vast majority of the energy in the cap, 16 joules. If I were to simply charge two supercaps in series and use the voltage directly, I'd only get to use a much smaller fraction of the stored energy as when the two series caps discharged to 7 volts, I'd be done. That also only allowed me to use about half the stored energy in the capacitors. That's the way other supercap based backup batteries are configured. The more efficient use of the stored energy allows me to make a smaller package with only one supercap. That allows the YLB to easily able to fit into the form factor of a 9V flat battery. Actually, it's considerably thinner than the flat battery.