If you replace the diode in a boost or buck converter with a second switch that is turned on and off complementary to the other one, they are the same circuit run in opposite directions. Just an observation.
You can use this observation to build a "buck-boost" topology that can make the output voltage larger or smaller than the input voltage. This is common for 1sNp Li-ion batteries that need a high-current 3.3V rail - buck from 4.2V to 3.3V at full charge, boost from 3V to 3.3V at low charge.
There's actually a bunch of ways to make buck-boost style converters that can do both functions, like the cuk and sepic topologies. There's also bidirectional bridge converters that can change input and output direction - you see this a lot on hybrid vehicles (12V to 48V or vice versa) and electric vehicles (48V to 400V and vice versa).
