Most of these power supplies use a transformer ... The second circuit presented adds voltage stabilization using a transistor and 78XX regulator. From there, zero-crossing detection is added ...

Though there is nothing spectacularly challenging about a power supply from the perspective ... it can be a shunt regulator, and there is even a circuit for its use as a switching regulator ...

Based on SMIC 0.18μm 3.3v/1.8v Logic process, this design of Low-Dropout (LDO) regulator is to provide both 3.3V and 1.8V supplies that are regulated from the single 5V input. The maximum output ...