Buck converters
A buck converter switches the input on and off rapidly and smooths it with an inductor and capacitor. The output is the input times the duty cycle, the fraction of time the switch is on. The inductor is chosen so that its current ripple is 20 to 40% of the output current: L = Vout × (Vin − Vout) ÷ (Vin × f × ΔI). A higher switching frequency allows a smaller inductor and capacitor.
Boost converters
A boost converter stores energy in the inductor while the switch is on, then releases it into the output at a higher voltage. The input current is higher than the output current by the voltage ratio, so the inductor and switch must handle it. The output capacitor supplies the whole load while the switch is on, so it needs more capacitance than a buck's.
Radio noise
Switching converters can cause interference on receivers, at the switching frequency and its harmonics. Keep the switching loop small, use a shielded inductor, add filtering on the input and output, and choose a frequency whose harmonics miss the bands you use. The harmonics calculator shows where they land. For a quiet linear alternative, see the LM317 calculator.
Questions
What is the duty cycle of a buck converter?
About Vout ÷ Vin, a little more to cover losses. 5 V from 13.8 V needs about 40%.
How do I choose the inductor?
For 20 to 40% current ripple, using L = Vout × (Vin − Vout) ÷ (Vin × f × ΔI), and rated for the peak current.
Why does my switching regulator cause radio interference?
Fast switching edges radiate harmonics. Shielded inductors, tight layouts, filtering and ferrites help.
When is a linear regulator better?
For low currents, small voltage drops, or very noise-sensitive radio circuits.