Every embedded power supply design starts with the same question: linear regulator (LDO) or switching converter (buck)? Efficiency is the obvious metric, but it’s rarely the deciding factor.
The efficiency argument
An LDO drops voltage and wastes the difference as heat: P_loss = (Vin - Vout) × Iout.
A 5 V → 3.3 V LDO at 200 mA dissipates (5 - 3.3) × 0.2 = 340 mW. That’s 1.7 V × 0.2 A. The efficiency is 3.3 / 5 = 66%.
A buck converter at the same operating point runs at 85–93% efficiency depending on the IC and load. At 90%, losses are about 73 mW vs 340 mW. That’s a real difference — especially in battery-powered designs.
Use the LDO calculator to calculate the thermal dissipation for your specific conditions. Above about 200–300 mW of dissipation, an LDO starts needing a heatsink or careful thermal PCB design, which often tips the cost/space comparison toward a buck converter.
When LDOs win
Low power loads. At 10 mA output, the LDO dissipates 17 mW. The efficiency difference between LDO and buck is real in percentage terms but trivial in absolute energy. A buck converter has quiescent current (typically 50–300 µA) that an LDO doesn’t. Below ~30 mA load, a good LDO (like the TLV70033, 1 µA Iq) is often more efficient.
Noise-sensitive analog. Buck converters switch at frequencies from 200 kHz to 3 MHz. That switching noise couples into your power rail and into analog circuitry. A MEMS microphone, ADC reference, or PLL supply that picks up 30 mV of switching noise will perform far below spec. LDOs have PSRR (power supply rejection ratio) that suppresses input noise — 60–80 dB at low frequencies. Run a noisy supply through an LDO before connecting to sensitive analog circuitry.
Simplicity and cost. An LDO is one IC and one or two capacitors. A buck converter requires an inductor, at least two capacitors, a feedback resistor divider, and careful layout. Bill of materials cost is 3–5× higher for the buck. If you’re doing high-volume production and the LDO thermal loss is acceptable, the BOM savings matter.
Space. A compact LDO in a SOT-23-5 package takes ~9 mm². A buck converter with inductor and capacitors takes 50–200 mm². On a small sensor PCB, that can be the deciding factor.
When buck converters win
High input voltage. Running a 3.3 V MCU from a 12 V supply? An LDO dissipates (12 - 3.3) × Iout = 8.7 V × Iout. At 100 mA that’s 870 mW — definitely needing a heatsink, and represents thermal stress on the package and PCB. A buck converter handles this efficiently.
High output current. Above 500 mA, an LDO’s thermal loss quickly requires a significant heatsink or spreads heat across a large PCB copper area. A buck converter at 1–3 A is a standard catalog part.
Battery-powered systems. Extending battery life by 30–40% through switching conversion is worth the added cost and complexity in IoT, wearables, and portable equipment.
The hybrid approach
Use a buck converter to step down to an intermediate voltage (say, 5 V), then use small LDOs from that 5 V rail for analog and RF supplies. The buck handles the bulk power conversion efficiently; the LDOs provide clean, noise-filtered power for sensitive circuits from a supply that’s already close to the target voltage (so thermal loss is small).
A common nRF52 design: USB or Li-Ion (3.6–5 V) → buck to 3.3 V for digital → LDO from 3.3 V to 1.8 V for analog/RF. The 3.3 V → 1.8 V LDO at 20 mA dissipates 1.5 × 0.02 = 30 mW — trivially low, and the LDO cleans up the buck’s switching noise before it reaches the RF section.
Use the buck converter calculator to size the inductor and capacitors, then verify the LDO thermal performance with the LDO calculator for any downstream linear regulators.