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

You probably use a smartphone, laptop or personal computer on a daily basis. These electronic devices use direct current (DC) to operate. However, since fireplaces are normally powered by high voltage alternating currents (AC), you will need to step down the voltage and convert the AC to DC using a power supply such as your power supply or charger.


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

Keep reading 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 direct current electronic devices. These devices are responsible for doing two things: lowering the voltage and converting alternating current to direct current. Although both devices step down and step down power, the difference in how they accomplish these tasks makes them better suited for certain applications.

A linear power supply is a device used in low noise and precision operations. Its use of heavy transformers and analog filters allows this power supply to produce clean voltages at the cost of low efficiency, heavier weight and larger size. Linear power supplies are best used in recording equipment, electric musical instruments, medical equipment, and high precision laboratory measuring tools.

A Switch Mode Power Supply (SMPS) is used for high efficiency and high current operations. Unlike linear power supplies, switching power supplies use solid-state components to modulate and regulate incoming voltages. These power supplies rely on high-frequency switching using power transistors, which makes them noisy but very energy efficient, lightweight and compact. Switch mode power supplies are often used in computers, phone chargers, manufacturing equipment and many low voltage electronic devices.

How does a linear power supply work?

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

Here is a schematic of a linear power supply:

A linear power supply works in three stages:

Step 1: Step down the high incoming AC voltage through the use of a transformer.

2nd step: The lowered voltage then passes through a full-bridge rectifier, which rectifies the AC voltage to pulsating DC voltages.

Step 3: Pulsed DC voltage signals pass through a filter made up of inductors and capacitors. This smoothing filter removes signal fluctuations from a pulsating DC voltage, making them usable for delicate electronic devices.

How does a switching power supply work?

Switch mode power supplies are complex devices that use solid state components to perform high frequency power switching and a smaller ferrite core transformer. These types of power supplies can step up and down voltages by using a DC feedback loop to control the output voltages.

Here’s how they work:

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

2nd step: After making sure that the circuit is well protected, the high voltage alternating current then passes through the second module consisting 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 direct current is then sent through a PWM driver, which takes into account and controls a power MOSFET which regulates the voltage by high frequency switching. Switching also transforms DC current into a square wave.

Step 4: The DC square wave now enters a ferrite core transformer, transforming the signals into AC square waves.

Step 5: AC square waves pass through a bridge rectifier, converting the signal to pulsating DC and then passing 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 or switching power supplies

There are different reasons why a power supply is chosen for use in specific applications. These would 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 the way they handle energy affects their performance and ease of use in certain applications.

Efficiency

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

Depending on their classification, switching power supplies can have an efficiency of 80 to 92%. This means that your device can produce 80-92% of the energy you put into it. Its efficiency comes from the use of smaller but efficient components that regulate voltages by low voltage high frequency switching.

In contrast, a linear power supply can only have 50-60% power efficiency due to its use of larger and less efficient components.

Signal noise and ripple

Although inefficient, linear power supplies make up for their inefficiencies with their stable, clean, and low-noise signal outputs. The use of analog components by a linear power supply allows them to process electricity smoothly and without switching, making their output low ripple or low noise.

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

Height and weight

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

As for switching power supplies, since they use small and light components, they can be designed to be small enough to be integrated 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 likely to break during operation, linear power supplies provide consistent and reliable outputs. The simplicity of design and use of the most common electronic components facilitates the supply of parts and the repair of linear supplies.

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

Profitability

In the past, linear power supplies were the most cost-effective devices due to their simple design and the use of fewer components. It also didn’t help that manufacturing semiconductor components was expensive. However, with semiconductors being more in demand, manufacturers have been able to scale up and make semiconductor components exponentially cheaper than before. This, in turn, makes many switch-mode power supply designs more cost effective than linear power supplies.

Using the Proper Power Supply

So that’s pretty much all you need to know about linear and switching power supplies. To ensure the safety of your electronic devices, always use the original chargers that came with the device, but if they are not available, you can always purchase an AC adapter.

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

Rosemary C. Kearney