Capacitor-coupled switched shunt regulator (CCSS) App note from Microchip. App note here.
Shunt regulators consist of two elements: a voltage regulator in parallel with the load (the shunt), and a series element between the supply and load to limit current. The parallel shunt regulates voltage by varying its conduction to maintain the desired voltage across the load. As the load current decreases, the shunt compensates by conducting more current. This results in high standby current consumption.
The switched shunt regulator operates similarly to a linear shunt regulator except current is proportioned between shunt and load in a switched (on/off) manner. When the switch is in the lower position it acts as a zero-ohm shunt. When in the upper position it diverts input current to the output. Since the switch is ideally zero ohms, it conducts current with no losses.