How do you choose between LDO and linear regulator for your circuit design?

1 What are linear regulators and LDOs?

Linear regulators and LDOs are both types of voltage regulators that use a series pass transistor to control the output voltage. The transistor acts as a variable resistor that adjusts its resistance according to the feedback from the output voltage. The difference between linear regulators and LDOs is the amount of voltage drop across the transistor. Linear regulators require a higher input voltage than the output voltage, typically by at least 2 V. This means that the transistor has to dissipate a lot of power as heat, which reduces the efficiency and increases the temperature of the regulator. LDOs, on the other hand, can operate with a much lower input voltage than the output voltage, typically by less than 0.5 V. This means that the transistor has less power dissipation and less heat generation, which improves the efficiency and reduces the temperature of the regulator.

2 When to use linear regulators?

Linear regulators are a popular choice for many applications due to their simplicity, affordability, and ease of use. With a low output noise and ripple, they are suitable for sensitive analog circuits, as well as having a fast transient response to adjust to changes in load current or input voltage. Linear regulators are ideal for applications with low current consumption, a large input-output voltage difference, and a stable input voltage. Some examples of linear regulator applications include powering microcontrollers, sensors, and logic devices; providing reference voltages for analog circuits; and isolating noise-sensitive circuits from noisy power sources.

3 When to use LDOs?

LDOs are more complex and expensive than linear regulators, and they typically have higher output noise and ripple, as well as a slower transient response, making them less suitable for sensitive analog circuits. Despite these drawbacks, LDOs have advantages that make them ideal for applications with high current consumption, small input-output voltage difference, and variable input voltage. Examples of LDO applications include powering RF circuits, audio amplifiers, LEDs, providing post-regulation for switching regulators, and extending battery life for portable devices.

4 How to choose between linear regulators and LDOs?

When deciding between a linear regulator and an LDO for a circuit design, there is no definitive answer. You should consider factors such as input voltage range, output voltage level, load current requirement, power efficiency, noise performance, transient response, cost, and board space. As general guidelines, use a linear regulator if you have a large input-output voltage difference, a low current consumption, a stable input voltage, and a noise-sensitive circuit. An LDO should be used if you have a small input-output voltage difference, a high current consumption, a variable input voltage, and a power-sensitive circuit. When there is a moderate input-output voltage difference with moderate current consumption and mixed noise and power sensitivity, you can choose either depending on preference and availability.