Basic principles and practical cases of switching power supply modules

In modern electronic devices, switching mode power supply (SMPS) plays a vital role. It not only provides efficient power conversion, but also demonstrates its unique advantages in various application scenarios. Whether in household appliances, industrial equipment, or in communications and computer systems, SMPS has shown its irreplaceable importance. This article will answer three key questions and explore the basic principles of SMPS, different topologies and precautions in practical applications to help readers better understand and apply this technology.

What is the basic principle of SMPS?

The basic principle of switching mode power supply is based on converting the input power supply to the required output voltage and current through high-frequency switching. Unlike traditional linear power supplies, SMPS controls voltage and current by quickly switching transistors to achieve efficient power conversion.

First, the input alternating current (AC) is converted into direct current (DC) through rectification and filtering. The DC power at this time is fed into a high-frequency switching circuit, which is usually composed of transistors or field-effect transistors (MOSFETs). By adjusting the on and off time (duty cycle) of these switches, the transmission of electrical energy can be controlled, thereby achieving regulation of the output voltage.

Next, the pulse voltage generated by the high-frequency switch passes through the transformer for voltage adjustment and isolation. The transformer not only regulates the voltage, but also provides electrical isolation to enhance the safety of the system. After passing through the transformer, the pulse voltage is rectified and filtered again, and finally outputs a stable DC power.

A significant advantage of high-frequency operation is that it allows the use of smaller transformers and inductors, which makes SMPS more compact and lightweight than traditional linear power supplies. In addition, SMPS is generally more efficient because it reduces energy loss during the conversion process. A typical application is the 12 volt power supply, which is widely used in various electronic devices to provide reliable power support.


What are the common topologies of SMPS?

Switched mode power supply (SMPS) can be divided into multiple topologies based on their circuit configuration and working mode, each of which has unique advantages and characteristics in different application scenarios. Understanding these common topologies will help you make more informed decisions when designing and selecting SMPS.

First, one of the most common topologies is the Buck converter. Buck converters are used to reduce higher DC input voltages to lower DC output voltages. Its working principle is based on controlling the on and off of the switching transistor, thereby regulating the current through the inductor and finally obtaining a stable low voltage at the output. Buck converters are highly efficient and simple in structure, so they are widely used in various electronic devices, such as 12 volt power supplies.

BUCK switching power supply architecture diagram

Another common topology is the Boost converter. In contrast to the Buck converter, the Boost converter is used to increase the lower DC input voltage to a higher DC output voltage. It achieves energy storage and release in the inductor through the control of the switching transistor, thereby increasing the output voltage. Boost converters are widely used in situations where voltage needs to be increased, such as electric vehicles and solar energy systems.

In addition, there is the Buck-Boost converter, which combines the Buck and Boost modes and can work when the input voltage is higher or lower than the output voltage, providing flexible voltage regulation capabilities. This topology is very practical in battery-powered devices because it can stabilize the output voltage when the battery voltage changes.

The Flyback converter is another important SMPS topology, which is often used in isolated power supply designs. The Flyback converter achieves electrical isolation between the input and output through a transformer, and regulates the output voltage by controlling the current storage in the primary winding of the transformer and the energy release in the secondary winding. Flyback converters are suitable for applications with lower power, such as adapters and small power modules.

Finally, there is the forward converter, which is also an isolated topology. Unlike the flyback converter, the forward converter transfers energy directly through the transformer, which provides higher efficiency and more stable output. This structure is often used in medium power range applications, such as communication equipment and industrial power supplies.

Understanding these different topologies can help us choose the most appropriate SMPS design according to specific application requirements to achieve the best performance and efficiency.

What should I pay attention to when using SMPS?

Although the switch mode power supply (SMPS) has many advantages, some key issues should also be paid attention to during design and use to ensure its stable and reliable operation.

First, EMI (electromagnetic interference) is an issue that requires special attention. Since SMPS operates at high frequencies, it will generate strong electromagnetic radiation, which may interfere with surrounding electronic devices. In order to reduce the impact of EMI, appropriate shielding and filtering measures can be added to the design. For example, EMI filters can be installed at the input and output ends, and metal shielding covers can be installed on key circuit parts to reduce electromagnetic radiation.

Secondly, thermal management is another major challenge in SMPS design. Although SMPS has high efficiency, some energy is still dissipated in the form of heat. In order to ensure the reliability of the power supply, an effective heat dissipation system needs to be designed, such as using heat sinks, fans or heat pipes. In addition, when laying out the PCB, the layout of the power components should be optimized as much as possible to improve the heat dissipation efficiency.


Furthermore, the selection and reliability of components are also key points that need to be paid attention to. SMPS involves a variety of high-frequency and high-power components, such as switching transistors, transformers and inductors. The performance and reliability of these components directly affect the overall performance and life of the power supply. Therefore, high-quality components should be selected during the design process, and rigorous testing and verification should be carried out.

In addition, the protection mechanism of the power supply, such as overvoltage, overcurrent, overtemperature and short-circuit protection, needs to be considered during the design process. These protection mechanisms can protect the power supply and load from damage under abnormal conditions and improve the safety and reliability of the system.

Finally, debugging and testing are also important links to ensure the reliability of SMPS. During the production process, comprehensive functional testing, aging testing and environmental adaptability testing should be carried out to ensure that the power supply can operate stably under various working conditions.

In specific applications, DC power supply is a common SMPS application, which provides reliable power support for various electronic devices through efficient and stable DC output.


As a core component in modern electronic devices, the switching power supply has been widely adopted in many applications due to its high efficiency, compactness and flexibility. By deeply understanding the basic principles of SMPS, different topologies and precautions for use, this technology can be better designed and applied, thereby improving the overall performance and reliability of electronic devices. Whether it is a 12V power supply or a DC power supply, the technological progress and application prospects of SMPS will continue to promote the development of the electronics industry and provide solid power support for various innovative applications.


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