Efficiency

Buck Converter: Much more efficient when the input-to-output voltage difference is large. A switching buck typically achieves 80–95% efficiency since it stores and transfers energy via an inductor rather than dissipating it as heat.

LDO: Efficiency equals Vout/Vin. If Vin is 12 V and Vout is 3.3 V, efficiency is only ~27%. LDOs are practical when Vin ≈ Vout (small dropout), but wasteful when Vin ≫ Vout.

Noise and Ripple

Buck Converter: Generates switching noise and ripple due to inductor charging/discharging and fast switching transients. Requires output LC filtering and careful PCB layout to minimize EMI.

LDO: Very low output noise and ripple, often used to “clean up” noisy rails. An LDO can follow a buck converter to provide a quiet, final regulated voltage for sensitive analog/RF circuits.

PCB Size and Complexity

Buck Converter: Requires inductor, switching MOSFET(s), diode (or synchronous MOSFET), and multiple capacitors. Layout is critical to prevent EMI.

LDO: Very simple—just the regulator IC and a couple of decoupling capacitors. Minimal layout sensitivity.

Cost

Buck Converter: More expensive due to inductors, switches, and higher part count.

LDO: Cheap and compact, often integrated into MCUs or SoCs for local regulation.