A 30 W solar battery charger with regulated 5 V and 3.3 V rails: an STM32G031 running perturb & observe MPPT and a CC/CV charge state machine, steering a TI LM5175 4-switch buck-boost through a single analog control input. Four-layer KiCad board, schematic and PCB generated from Python, with an electrothermal simulation run against the published board file.