Linear vs. switching power supplies: what’s the difference?

You probably use a smartphone, laptop or PC every day. These electronic devices use direct current (DC) to operate. However, since households are normally powered by high voltage alternating current (AC), you will need to lower the voltage and convert alternating current to direct current by using a power supply, such as your power block or charger.


The most common power supplies in use today are the linear and switching power supplies. Knowing which one to use for specific applications will keep your electronics safe and functioning optimally.

Read on below for a comparison between linear and switching power supplies.


What are linear and switching power supplies?

Linear and switching power supplies are electrical devices used to power and charge electronic DC devices. These devices are tasked with doing two things: lowering the voltage and converting alternating current to direct current. While both devices reduce and correct power, the difference in how they perform these tasks makes them better suited to certain applications.

A linear power supply is a device used in low-noise and precise operations. Using heavy duty transformers and analog filters, this power supply can deliver clean voltages at the expense of low efficiency, heavier weight and larger size. Linear power supplies are best used in recording equipment, electrical musical instruments, medical equipment, and high-precision laboratory measurement instruments.

A switching or switching power supply (SMPS) is used for highly efficient and high currents. Unlike linear power supplies, switching power supplies use solid-state components to modulate and control incoming voltages. These power supplies rely on high-frequency switching using power transistors, making them noisy but highly energy efficient, lightweight and compact. Switching power supplies are commonly used in computers, phone chargers, manufacturing equipment, and many low-voltage electronic devices.

How a linear power supply works

Using purely analog components available in the 1950s, linear power supplies had to rely on heavy current transformers and bulky electrolytic capacitors to lower and correct voltages. Although transistors were already being mass-produced back then, high AC voltages simply produced too much heat for transistors to handle.

Here is a schematic of a linear power supply:

A linear power supply works in three steps:

Step 1: Reduce the incoming high AC voltage by using a transformer.

Step 2: The reduced voltage then passes through a full bridge rectifier, which rectifies AC voltages to pulsating DC voltages.

Step 3: The pulsating DC voltage signals pass through a filter consisting of coils and capacitors. This smoothing filter removes the signal fluctuations from a pulsating DC voltage, making them useful for delicate electronic devices.

How a switching power supply works

Switching power supplies are complex devices that use solid-state components to run high-frequency power switching and a smaller ferrite core transformer. These types of power supplies can increase and decrease voltages by using a DC feedback loop to control the output voltages.

This is how they work:

Step 1: The high voltage alternating current enters the power supply through a circuit protection module consisting of a fuse and an EMC filter. The fuse is for surge protection and the EMC filter protects the circuit from the signal ripples coming from the unfiltered AC power.

Step 2: After ensuring that the circuit is properly protected, the high voltage AC power is then passed through the second module which consists of a full bridge rectifier and a smoothing capacitor. The full bridge rectifier converts alternating current into pulsating direct current, which is then smoothed by a capacitor.

Step 3: The high-voltage DC is then sent through a PWM driver, which receives feedback and drives a power MOSFET that regulates the voltage through high-frequency switching. The switching also makes the straight DC current into a square wave.

Step 4: The DC square wave now enters a ferrite core transformer and transforms the signals back to AC square waves.

Step 5: The AC square waves pass through a bridge rectifier, convert the signal into pulsating DC current, and then pass it through a smoothing filter. The final output is then used to send signals to the PWM driver, which creates a feedback loop that regulates the output voltages.

Linear vs. switching power supplies

There are several reasons why a power supply for specific applications is chosen. These often include efficiency, noise, reliability and repairability, size and weight, and cost. Now that you have a general idea of ​​how they work, here’s how their way of energy processing affects their performance and usability in certain applications.

efficiency

Because electricity must pass through a series of electrical and electronic components, the process of correcting and controlling voltages will always have inefficiencies. But how much?

Depending on how they are rated, switching power supplies can have an efficiency of 80 – 92%. This means that your device can produce 80-92% of the energy you put into it. The efficiency comes from using smaller but efficient components that regulate voltages through high frequency low voltage switching.

In contrast, a linear power supply can only be 50 – 60% energy efficient due to the use of larger and less efficient components.

Signal noise and ripple

Though inefficient, linear power supplies make up for their inefficiencies with their stable, clean, low-noise signal outputs. Using analog components of a linear power supply allows them to process the electricity in a smooth and non-switchable manner, making their output ripple or noiseless.

On the other hand, switching power supplies rely on high-frequency switching of low voltages to reduce heat, have better efficiency, and produce a lot of noise! The amount of signal noise depends on the design and quality of the specific switching power supply.

Size and weight

The size and weight of a power supply can greatly affect its application to smaller electronic devices. Since linear power supplies use heavy and bulky components, their use on discrete electronic devices is impossible unless you use the power supply as a charger.

As for switching power supplies, since they use small and lightweight components, they can be designed to be small enough to integrate into already smaller devices. The low weight and small size of a switching power supply combined with its energy efficiency make it applicable to the vast majority of portable electronic devices.

Reliability and repairability

With fewer parts to break during operation, linear power supplies provide consistent and reliable outputs. The simplicity in design and use of more common electronic components makes it easier for people to buy parts and repair linear supplies.

With significantly more delicate components, switching power supplies are more likely to break before a linear power supply would. However, good design and the use of high quality components can make switching power supplies very reliable, perhaps as reliable as linear power supplies. The real problem with switching power supplies is that they are increasingly difficult to repair the more complex their design is.

Cost efficiency

In the past, linear power supplies were the most cost-effective device due to their simple design and the use of fewer components. It also didn’t help that the manufacture of semiconductor components was expensive. However, as the demand for semiconductors increased, manufacturers were able to scale up and make solid-state components exponentially cheaper than before. This, in turn, makes many switching power supply designs more cost-effective than linear power supplies.

Using the right nutrition

So that’s about all you need to know about linear and switching power supplies. To make sure your electronic devices are safe, always use the original chargers that came with the device, but if they aren’t available, you can always buy a power adapter.

Before you buy, remember that linear power supplies are ideal for electronics used for precision applications such as electric musical instruments, radios and medical devices, while switching power supplies are used for high-efficiency situations such as computer power supplies, chargers and lighting.

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