It's a fairly simple PSU with 12V battery backup.
It manages the charging and discharging of the battery.
I have built and tested the discrete version on a double sided PCB that I had made. (no SM components)
I have used a dual comparator (LM393) for voltage measurement.
Features include:
> Battery charge indication (red/green led)
> Changeover relay for mains supply/battery based on mains availability.
> Low voltage cutout to protect battery when fully discharged (with built-in hysterisys to stop relay energing when load is disconnected & battery voltage recovers).
> Battery charge current limitation to prevent overloading supply.
I have used 13 resistors, 1 preset pot, 5 capacitors, 3 diodes, 1 comparator, 1 voltage reference IC & 2 transistors.
All voltages are < 15 Vdc.