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Linear Power Supply vs. Switching Power Supply: Definition and Principles

Date:2021.07.30   Views:2062

Everyday electronic devices, especially those with integrated circuits, need a reliable source of DC voltage that can be powered at all times without any problems. In this blog, we will examine two power supply design topologies for you to consider for your next project, linear regulated power supplies and switching power supplies. The power supply you choose ultimately depends on your requirements for efficiency, space, output regulation, transient response time, and cost.

Linear Regulated Power Supplies

Until the 1970s, linear regulators were the power supply of choice for converting alternating current (AC) to stable direct current (DC) for electronic devices. Although this power supply type is not commonly used today, it remains the best choice for applications requiring minimal noise and ripple.

How they work?

The main component that makes a linear regulator work is the steel or iron transformer. This transformer provides two functions. It acts as a barrier to isolate the high-voltage AC input from the low-voltage DC input, while filtering out any noise that enters the output voltage. It reduces the AC input from 115V/230V to approximately 30V, which can then be converted to a stable DC voltage.

The AC voltage is first stepped down by a transformer and then rectified by several diodes. It is then smoothed to a low DC voltage by a pair of large electrolytic capacitors. This low DC voltage is then regulated to a stable output voltage using transistors or integrated circuits.

Switching Power Supply

Switching Power Supply

Switching Power Supply (SMPS)

Switching power supplies were introduced in the 1970s and quickly became the most popular way to provide DC power to electronic devices. What made them so great? They stand out for their high efficiency and performance compared to linear regulators.

How they work?

Switching mode power supplies regulate the output voltage through pulse-width modulation (PWM). This process generates high frequency noise, but it provides high efficiency ratings in a small footprint. When plugged into an AC power supply, 115V or 230VAC is first rectified and smoothed by a set of diodes and capacitors to provide high voltage DC. This high DC voltage is then reduced using a small ferrite transformer and a set of transistors. The step-down process still maintains a high switching frequency between 200kHz and 500kHz.

The low DC voltage is eventually converted to a stable DC output through another set of diodes, capacitors and inductors. Any regulation needed to keep the output voltage consistent is handled by adjusting the pulse width of the high frequency waveform. This regulation process works through a feedback circuit that continuously monitors the output voltage and controls the switching ratio of the PWM signal as needed.

Switching Power Supply

Preferred Applications

You will often find switching power supplies used in applications where battery life and temperature are important, such as

Electrolysis, waste treatment or fuel cell applications

DC motor, tanker, aerospace and marine applications

R&D, manufacturing, and testing equipment

Battery charging of lithium-ion batteries for aerospace and vehicles

Electroplating, anodizing and electroforming processes

Linear Power Supply vs. Switching Power Supply

Switching power supplies may be more efficient than linear regulators, and some of the advantages to consider include

Small form factor The step-down transformer in the SMPS operates at high frequencies, which reduces its size and weight. This allows the switching power supply to have a much smaller form factor than a linear regulator.

High efficiency. The voltage regulation in a switching power supply is performed without excessive heat emission.

Flexible applications. Additional windings can be added to the switching power supply to provide multiple output voltages. Transformer isolated SMPS can also provide output voltages independent of the input voltage.

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