Floating the regulators to support high voltages
A linear regulator operates by using a voltage-controlled current source to force a fixed voltage to appear at the regulator output terminal. The control circuitry must monitor (sense) the output voltage, and adjust the current source (as required by the load) to hold the output voltage at the desired value. Any regulator has datasheet specifications controlled by the semiconductor process. To operate the device safely without crossing the absolute maximum limits of the regulator, it needs some tricks to float the voltage levels.