Boost Converter

The switch charges the inductor from the input; when it opens, the inductor's voltage adds to the input and pushes current through a diode into the output capacitor:

$V_{out} = \frac{V_{in}}{1 - D}$

Example: 3.7 V Li-ion to 5 V needs $D$ ≈ 0.26. Input current is higher than output current (power is conserved), so make sure the battery and inductor can handle it. Uses: USB power banks, LED drivers, single-cell gadgets.