Voltage regulators: LDO or switching converter?
Linear regulators (LDO) versus switching converters (buck, boost): dropout voltage, efficiency, heat dissipation, noise, quiescent current and how to choose for a battery or 12 V product.
Linear regulators and LDOs
A linear regulator lowers the voltage by burning the difference as heat. The input current equals the output current, so the power lost is P = (Vin − Vout) × I. An LDO (low-dropout) can regulate with a small difference between input and output, typically 0.1 to 0.3 V. Simple, quiet, cheap.
The heat calculation
From 12 V down to 3.3 V at 200 mA: (12 − 3.3) × 0.2 = 1.74 W of heat. A regulator in a SOT-23 package has a thermal resistance of roughly 150 to 250 °C/W to the air, which would mean hundreds of degrees of temperature rise. It goes into thermal shutdown, or worse. From 5 V to 3.3 V at 50 mA, the same regulator dissipates 85 mW and is perfectly fine.
Switching converters
A buck converter chops the input with a transistor and smooths it with an inductor and capacitors. Efficiency is typically 85 to 95 %, so the same 12 V to 3.3 V at 200 mA wastes about 0.1 W instead of 1.7 W. The cost: more parts, switching noise that must be managed in the layout, and a design that has to follow the datasheet closely. A boost converter raises the voltage, for example from one Li-ion cell to 5 V.
How to choose
| Situation | Choice |
|---|---|
| Small voltage difference, low current | LDO |
| Large difference or current above ~100 mA | Buck converter |
| Output higher than input | Boost converter |
| Noise-sensitive analog, RF | LDO, or buck followed by an LDO |
| Battery device that sleeps | Either, but check quiescent current (µA) |
A switching converter that works on the bench can fail EMC tests, ring, overheat at high ambient or become unstable with a different capacitor. Designing, laying out and measuring converters is exactly what our power electronics work covers.
Parts and tools to practise
| Item | What to look for | Buy |
|---|---|---|
| Voltage regulator modules | Small buck converter and LDO modules to power experiments safely. | View on Amazon ↗ |
| Adjustable bench power supply with current limit | 0 to 30 V, 0 to 5 A. The current limit saves boards on first power-up. | View on Amazon ↗ |
| Digital multimeter | Auto-range with continuity beeper, CAT III rated. You will use it every day. | View on Amazon ↗ |
| The Art of Electronics (Horowitz and Hill) | The reference book. Dense, but worth it for anyone serious. | View on Amazon ↗ |
Links go to Amazon. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. We only list tools of the kind we use on our own bench.
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