DC-DC Converters

In continuous conduction mode with duty cycle $D$:

Converter	$V_{out}/V_{in}$	Notes
Buck	$D$	step-down
Boost	$\dfrac{1}{1-D}$	step-up
Buck-boost	$-\dfrac{D}{1-D}$	inverted output
Ćuk / SEPIC	$\dfrac{D}{1-D}$	SEPIC non-inverting
Flyback	$\dfrac{N_s}{N_p}\cdot\dfrac{D}{1-D}$	isolated, low power (< ~150 W) chargers
Forward	$\dfrac{N_s}{N_p}D$	isolated, medium power

These follow from volt-second balance on the inductor: the average voltage across an inductor in steady state is zero. Isolated converters use a high-frequency transformer, which is far smaller than a 50 Hz transformer.