What is the difference between linear power supply and switching power supply?

Electronic products are increasingly updated quickly, coupled with electronic green advocacy, so electronic products pay more attention to energy efficiency, green environmental protection. Therefore, on the one hand, the package is made smaller in the linear voltage regulator power supply, with lower energy consumption. On the other hand, increase the development of switching power supply technology to solve the power consumption from the source, to achieve the green switching power supply products.

Linear power supply working principle

This diagram is the linear power supply working principle diagram. The error amplifier in the chart to capture the feedback signal used to control the MOSFET (crystal transistor) gate signal, through the control of the current flowing through the transistor to handle the voltage drop of the adjustment tube to output a stable voltage, so this power supply is also called a linear power supply.

Working principle of switching power supply

This diagram shows

Switching power supply working principle diagram. The error amplifier in the chart is used to capture the feedback signal for controlling the gate signal of MOSFET (crystal triode) Q1 to control the switching of Q1. Through the switch of Q1 to achieve Lo and Co energy storage work to ensure a stable voltage output. Q1 works in the cutoff or saturation state at this point in the figure, so this power supply is called a switching power supply.

Linear power supply and switching power supply

The adjustment tube of the linear power supply works in the amplification state. It has a large heat generation, low efficiency, and a large heat sink volume. At the same time, it also requires the same large volume of frequency transformer if the linear power supply of multiple voltage output volumes will be even more significant.

Switching power supply regulator tube work in the saturation/cutoff state, heat generation is small, high efficiency, large transformer volume to save. But the switching power supply output DC will be superimposed on the more significant ripple, which can improve the output side with a voltage regulator diode, addition is the switching power supply will generate a considerable spike pulse interference, so the circuit needs to be connected in series with magnetic beads to improve. There are not so many disadvantages to linear power supply, and the ripple can be tiny.


First of all, they are both power supplies that provide a stable voltage or current to the load within the rated specifications. But they have different means to achieve the purpose. The range of adaptation is also not quite the same.

The working principle of linear power supply is simple. It can equate its working process to an adjustable resistor, and the part of the voltage above the required voltage is turned into heat when it is bucked and consumed. It is like making a table of ten people if only one person menu. The linear power supply approach is to find nine people to help eat. Therefore, the greater the step-down, the lower the efficiency, the greater the waste.

So the linear power supply is not suitable for high voltage differential circuits and can only step down, not step up. Because the transistors in this power supply work in the linear amplification area rather than the switching state, the output is smooth and clean without harmonics. No interference with the load is more suitable for precision equipment.

Advantages of switching power supply

The most significant advantage of switching power supply is high efficiency, so it is more suitable for high voltage difference and high power occasions. If you also use the analogy of a banquet, it will automatically adjust the amount of food according to the number of people on the menu. There are a few people to do a few people’s meals, will not be wasted.

Its name is called switching power supply because its internal power devices work in the switching state, which is the key to its high efficiency. People usually discuss how to save electricity. Some people answer most: no need to keep the most! This would have been gambling and flirting word, but the switching power supply is developed according to this principle. It uses the complete conduction and complete cutoff of the two states alternately, unlike the linear power supply as a large resistor in a moment of constant consumption of “excess” power.

The switching power supply has a meager internal resistance during conduction, and no energy consumption during cutoff, so it has very high efficiency. This circuit uses different times (i.e., duty cycle) to adjust the on and off to achieve additional energy transfer. Because of this on/off frequency of tens of thousands of times per second, the transformer inside the power supply can be made very small, thus achieving the miniaturization of the size of the power supply while also allowing can use of the switching power supply to step down and step up. It is currently the most widely used power supply.

Disadvantages of switching power supply

However, the disadvantage of switching power supplies is also apparent: the large number of harmonics generated by the switching process of power tubes. Due to the high frequency and complex spectrum, it isn’t easy to filter out. These interferences can be spread with the wire can also be radiated to space, so the external interference is severe and now almost a public hazard.

Switching power supply does not have the main transformer, rectified DC power, and then through the power switch tube frequency regulation step-down. Linear power supply mainly relies on the main transformer step-down directly. The principle of the two power supplies is like the old kind of big and bulky copper wire welding machine and now small and cheap welding machine. At the same time, To step down and achieve the necessary power, the linear power supply must have a large main transformer. Still, it outputs electricity without pulses, which has the advantage of being suitable for electronic fields such as computer power supplies. Continuous power supply will not affect the pulse-sensitive computer.

However, it can’t say switching power supply terrible. It dramatically reduces the quality of the transformer and high efficiency of electrical conversion, so some industrial areas are very suitable for these switching power supplies, such as the IGBT tube tig arc welding machine.

Of course, many things now also use the advantages of linear power supply and switching power supply integrated into the power supply, and for example, high-power computer power supply, to improve the efficiency of higher electrical conversion, with changing tubes, but also to stabilize the voltage and current output, but also with the use of transformers and capacitors.


Ena Leung

Ena Leung

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