In PCB design, there are no more than two kinds of common power devices, DC/DC and LDO.

LDO is a low dropout linear regulator, or a low voltage drop device, which is generally used for occasions requiring depressurization. It has the advantages of low cost, low noise and small quiescent current. It requires few external components and usually only requires one or two bypass capacitors.
The main reason for the performance of the LDO linear regulator is that the regulator tube is P channel MOSFET. P channel MOSFET is voltage driven and does not require current, so it greatly reduces the current consumed by the device itself. In addition, the voltage drop on the P channel MOSFET is approximately equal to the product of the output current and the on resistance. Because of the small on resistance of the MOSFET, the voltage drop above it is very low.

DC/DC means DC to DC (different DC power conversion), as long as this definition can be called DC/DC converter, including LDO. But generally speaking, the device that converts the direct current to the direct current by means of a switch is called DC/DC.

The DC/DC includes step-up, step-down, step-up / step-down, and reverse equal circuits. DC/DC converter has the advantages of high efficiency, high output current and small quiescent current. With the improvement of integration, many new DC/DC converters require only a few external inductors and filter capacitors. However, the output ripple and switching noise of this kind of power controller are relatively large and the cost is relatively high.

How to select?

If the input voltage is very close to the output voltage, it is better to use the LDO regulator to achieve high efficiency and, above all, low cost. Peer expert summed up the applications for LDO: such as the need to suppress the high requirements of the power supply noise suppression and the ripple of the products, such as PCB in a small area, such as mobile phone and other handheld electronic products, such as the power supply circuit does not allow the use of inductors, such as mobile phone and other products, such as the power output state with instantaneous calibration and self checking function for example, the regulator requirements of low pressure drop, its low power consumption products, such as requiring low cost and simple circuit scheme of products.

If the input voltage and the output voltage difference, or pressure drop, it should consider the use of switch type DC/DC, because the input current of LDO is basically equal to the output current, if the drop is too large, the energy consumption in LDO is too large, the efficiency is not high, so DC/DC is very suitable. DC/DC although high efficiency, you can output large current, but at the same time output interference is larger, the volume is relatively large, the cost is slightly higher.

Conclusion: step-up is necessary to select DC/DC, while the buck is to choose DC/DC or LDO, in terms of cost, efficiency, noise and performance on the analysis.