Giorgos from PCBheaven designed an SMPS buck regulator with 2xAA NiMh battery trickle charger and power failure output:
Some time ago I presented a small circuit with the MCP1640, the High Efficiency Battery Boost Regulator using the MCP1640. My original intention was to combine it with this one and make a complete power supply unit with SMPS technology, dual voltage output, battery charger and power failure signal output. And here it is!