What type of linear regulator is used in applications requiring efficient utilization of the primary power source?

A series linear regulator places the control element (typically a transistor) in series with the load. It regulates the output voltage by acting as an automatic variable resistor, drawing only the current actually required by the load. This makes it far more efficient in utilizing the primary power source than alternative linear designs. In contrast, a shunt regulator places the control element in parallel with the load. A shunt regulator must continuously draw total system current to maintain the voltage, shunting excess current to ground even when the load is disconnected, which makes it highly inefficient for general power supply applications.