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LDO vs Switching Regulator: Key Differences Explained

Both produce a stable voltage from a DC input voltage, but they handle the excess voltage differently. Linear regulators such as LDOs use a transistor like a variable resistor and dissipate the difference between input and output voltage as heat. Switching regulators turn transistors on and off at high speed and transfer energy through an inductor and capacitor, so they stay efficient even with a large voltage difference and can also boost. In exchange, switching produces ripple and noise.

AspectLDO (linear regulator)Switching regulator
How it worksThe output transistor operates in its linear region and drops the difference between input and output voltageTransistors switch on and off, and an inductor and capacitor transfer energy
EfficiencyRoughly output voltage ÷ input voltage. Producing 1.0 V from 1.8 V gives about 56%About 80 to 95% depending on conditions, even with a large voltage difference
Heat(input voltage − output voltage) × current all becomes heatLosses are small, so little heat is generated
Output noiseVery low. No switching noiseRipple at the switching frequency and harmonic noise (EMI)
Switching frequencyNoneAbout a few hundred kHz to a few MHz
Part countFew: about an IC plus input and output capacitorsMany: inductor, capacitors and, depending on the topology, diodes
Board designSmall and simpleThe inductor takes space, and layout must be careful to keep noise down
Boost and inversionNot possible. Step-down only, and the input must exceed the output by at least the dropout voltageStep-down, step-up, buck-boost and inversion are possible
Response to load changesFastSet by the control loop bandwidth, and often slower than an LDO
CostLowHigher, because of the extra parts
Typical usesSupplies for noise-sensitive circuits such as ADCs, PLLs and RF circuits, small voltage differences, low currentsCPU and SoC core supplies, high currents, efficient conversion from batteries, when boosting is needed

Figures are typical orders of magnitude and vary by process generation and product.

When to use which

LDO (linear regulator)
When the input-output voltage difference is small, the current is low, or for supplies to circuits where low noise matters, such as ADCs, PLLs and RF circuits.
Switching regulator
When the voltage difference is large, the current is high, you want long battery life, or you need a voltage higher than the input.
Combined
A common arrangement steps the voltage down efficiently with a switching regulator and then places an LDO after it to remove ripple. The LDO's input-output voltage difference is small, so its loss stays small too.

FAQ

How do you calculate LDO efficiency?

The same current flows at the input and output, so ignoring the LDO's own current consumption, efficiency is roughly output voltage ÷ input voltage. From 5 V to 3.3 V it is about 66%, and from 3.6 V to 3.3 V about 92%; the smaller the voltage difference, the higher the efficiency.

Why are switching regulators so efficient?

The transistors are used fully on or fully off. When on, the voltage across them is almost zero, and when off, the current is almost zero, so the loss, which is the product of voltage and current, is small except during transitions and similar moments.

What is the dropout voltage of an LDO?

It is the minimum difference between input and output voltage needed to keep the output at its specified voltage. In an LDO it can be as small as about 0.1 to 0.3 V, and if the input falls below that, the output voltage drops as well.

Check your understanding

Compared with a linear regulator (such as an LDO), which is a characteristic of a switching regulator?

  1. ALower efficiency but very low noise
  2. BIt outputs AC
  3. CHigh power-conversion efficiency, but switching tends to produce noise
Show answer and explanation

Answer: C. High power-conversion efficiency, but switching tends to produce noise

A switching regulator turns transistors on and off at hundreds of kHz to several MHz and transfers energy through inductors and capacitors, achieving about 80–95% efficiency even with large voltage differences, and it can also boost or invert. A linear regulator burns the difference as heat, so its efficiency is roughly Vout ÷ Vin (about 28% for 12 V to 3.3 V). Noise-sensitive circuits commonly follow a switcher with an LDO.

What does the dropout voltage of an LDO (low-dropout linear regulator) mean?

  1. AThe maximum output voltage
  2. BThe change in output voltage when the load is removed
  3. CThe minimum voltage difference between input and output needed to keep the output at its specified voltage
Show answer and explanation

Answer: C. The minimum voltage difference between input and output needed to keep the output at its specified voltage

Dropout voltage is the minimum input-output difference at which a regulator can still hold its output. LDOs use a PMOS (or similar) pass transistor to bring it down to about 0.1–0.3 V—for example, producing 2.8 V from a lithium-ion cell (3.0–4.2 V). Loss is (Vin − Vout) × current, so a small difference means better efficiency. With high ripple rejection, LDOs are widely used to power noise-sensitive circuits.

Why is a switching power supply more efficient than a linear power supply, which operates its transistor linearly?

  1. ABecause the transistor is used fully on or fully off, minimizing the time it sees voltage and current at once
  2. BBecause it uses no transistors
  3. CBecause its output voltage is always higher than its input
Show answer and explanation

Answer: A. Because the transistor is used fully on or fully off, minimizing the time it sees voltage and current at once

Transistor loss is voltage times current. A linear supply makes the transistor absorb the excess voltage while carrying the load current, so converting 12 V to 5 V is only about 42% efficient. A switching supply uses only the on state (almost no voltage) and off state (almost no current), losing little except during transitions, and reaches over 90% efficiency. It does require noise countermeasures.

  1. What is the closest efficiency of a linear regulator (LDO) producing 1.0 V from a 1.8 V input (ignoring the regulator's own quiescent current)?
  2. Which DC-DC converter outputs a DC voltage higher than its input?
  3. An LDO with a PSRR (power supply rejection ratio) of 60 dB at 1 kHz has a 1 kHz, 100 mV ripple on its input. Which is the guide for the ripple appearing at the output?

Practice Analog and electronic circuits questions

Key terms explained

LDO
Short for low-dropout regulator: a linear regulator that works with only a small difference between input and output voltage. It is low-noise, but the voltage difference times the current is lost as heat.
DC-DC converter
A circuit that converts one DC voltage into another. Using switches, inductors and capacitors, buck types lower the voltage and boost types raise it.
PSRR (power supply rejection ratio)
A measure of how little supply-voltage variation reaches a circuit's output. The larger it is, the more immune the circuit is to supply noise.
Power management IC (PMIC)
An IC that generates multiple voltages from a battery or similar and manages power-up sequencing and voltage changes.

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