Answer 4—The circuit is one way to create a buck/boost regulator using a single coil. When the input voltage is less than the desired output voltage, switch #1 is held closed and switch #2 is operated as in the boost regulator described previously. When the input voltage is higher than the desired output voltage, switch #2 is held open and switch #1 is operated as a buck regulator. 

Contributor: David Tweed