In modern electronic devices, the Switch Mode Power Supply (SMPS) is a widely used power conversion technology. It has been widely used in various occasions due to its advantages such as high efficiency, small size and light weight. However, SMPS also generates harmonics during operation, which may interfere with the power system and other electronic equipment. This article will introduce in detail what SMPS is and how it generates harmonics during operation, especially in the application of NVVV brand products.

1. What is a Switch Mode Power Supply (SMPS)?

A Switch Mode Power Supply (SMPS) is a power supply device that converts input voltage into the required output voltage through high-speed switching elements. Its core feature is to use pulse width modulation (PWM) technology to adjust the output voltage by controlling the on and off time of the switching element. Compared with traditional linear power supplies, switched mode power supply has higher efficiency and smaller size, so it has been widely used in various electronic devices.

Basic working principle of SMPS

The basic working principle of SMPS can be divided into several steps:

Rectification and filtering: The input alternating current (AC) is first converted into direct current (DC) through a rectifier circuit. This process is usually achieved through a full-wave rectifier bridge. The rectified DC usually has some ripples (i.e. the remaining AC component), so the waveform needs to be smoothed by a filter capacitor.

High-frequency switching: The smoothed DC is fed into the high-frequency switching circuit. The high-frequency switching circuit is the core part of the SMPS. It converts DC into a high-frequency pulse signal through the high-speed switching action of switching elements such as MOSFET or IGBT. The duty cycle of this high-frequency pulse signal determines the size of the output voltage.

Transformer: The high-frequency pulse signal is fed into a high-frequency transformer. The transformer can not only adjust the voltage, but also provide electrical isolation. High-frequency transformers are usually small in size but highly efficient, which is one of the important reasons why SMPS can be small in size.

Rectification and filtering: The high-frequency pulse signal after the transformer is rectified and filtered again, and the output is a stable DC voltage for the load.

Feedback control: SMPS is usually equipped with a feedback control circuit, which dynamically adjusts the on-time of the switching element by monitoring the output voltage and current to ensure the stability of the output voltage.

In practical applications, the output voltage of SMPS can be precisely controlled by adjusting the duty cycle of pulse width modulation (PWM). This allows SMPS to provide stable voltage output under various load conditions.

Advantages of SMPS

Compared with traditional linear power supplies, SMPS has many advantages:

High efficiency: Since SMPS regulates voltage by high-speed on and off of switching elements, energy loss is relatively small, so the efficiency is usually between 80%-90%, and some high-end products can even achieve higher efficiency.

Small size and light weight: Due to the high-frequency working principle, the transformer and filter elements in SMPS can be designed to be very small, which makes the overall power supply unit more compact and lightweight.

Wide input voltage range: SMPS can work stably within a wide input voltage range, which makes it more widely used worldwide, whether in the 110V American market or the 220V European and Asian markets, it can work normally.

Flexible output voltage: By adjusting the parameters in the control circuit, SMPS can provide a variety of different output voltages to meet different application requirements. For example, the NVVV brand 24VDC power supply is achieved in this way, and it is widely used in industrial automation, communication equipment and other fields.

However, despite the many advantages of SMPS, its high-frequency switching operation also causes some problems, the most important of which is the generation of harmonics.

2. How does SMPS generate harmonics?

Harmonics refer to voltage or current components with frequencies that are integer multiples of the fundamental frequency in addition to the fundamental frequency (usually 50Hz or 60Hz) in the power system. These harmonic components will interfere with the normal operation of the power system, causing equipment overheating, increased noise, reduced efficiency, and even equipment failure.

Relationship between high-frequency switching action and harmonics

The working principle of SMPS determines that it will generate harmonics. Specifically, the high-frequency switching elements (such as MOSFET or IGBT) in SMPS will generate high-frequency pulses when they are turned on and off. These high-frequency pulses appear as a series of harmonic components in the frequency domain.

Since the switching frequency of SMPS is usually between tens of kilohertz and hundreds of kilohertz, these high-frequency pulses introduce a large number of harmonics in the power system. The generation process of harmonics is as follows:

Switching element conduction: When the switching element is turned on, the current increases rapidly, and this process is manifested as high-frequency components in the frequency domain. These high-frequency components appear in the current and voltage waveforms in the form of harmonics.

Switching element turn-off: When the switching element is turned off, the current is suddenly interrupted, generating a transient voltage. This transient voltage also contains high-frequency components, further enhancing the intensity of harmonics.

Pulse width modulation (PWM): In SMPS, changes in the switching frequency and duty cycle of PWM control will also affect the distribution of harmonics. Especially when the load changes greatly, the instability of the PWM signal may lead to an increase in harmonic content.

These high-frequency harmonic components propagate through the power line, which may cause electromagnetic interference (EMI) to other equipment and cause harmonic distortion in the power system.

Impact of Harmonics on Power Systems

The impact of harmonics on power systems is multifaceted, mainly including the following points:

Voltage distortion: The presence of harmonics will cause the voltage waveform in the power system to be distorted, resulting in so-called voltage distortion. This distortion will affect the normal operation of the equipment, resulting in reduced equipment efficiency or even damage.

Current distortion: Harmonics will also cause distortion of the current waveform, increase the reactive power consumption of the equipment, cause overheating of power equipment (such as transformers, motors), and may shorten their service life.

Electromagnetic interference (EMI): The high-frequency harmonics generated by switching mode power supply will propagate through the power lines and cause electromagnetic interference to nearby electronic equipment. This interference may cause noise, signal loss and other problems in communication equipment, and may even cause sensitive equipment (such as medical equipment) to malfunction.

Degraded power quality: A large number of harmonics will reduce the power quality of the power system, reduce the overall efficiency of the system, and increase power loss.

For brands like NVVV, reducing harmonic generation and improving the power quality of power supply units is an important part of product design. This involves not only improving the quality and performance of switching components, but also the application of harmonic suppression technology.

3. How to reduce the harmonics generated by SMPS?

In practical applications, although the generation of harmonics is difficult to completely avoid, the impact of harmonics on the power system can be effectively reduced by optimizing the design and using advanced technologies. Below we will explore some common harmonic suppression methods and the application of the NVVV brand in this regard.

Use of filters

Filters are one of the most common means of harmonic suppression. By adding a low-pass filter to the input or output of the SMPS, the propagation of high-frequency harmonics can be effectively blocked and the impact on the power system can be reduced.

Input filter: Adding an LC low-pass filter to the input of the SMPS can suppress the harmonics entering the device from the power supply side. This filter can effectively reduce the transmission of high-frequency harmonics and protect the stability of the power supply system.

Output filter: Adding an LC filter to the output can reduce the harmonic content of the SMPS output, thereby reducing the impact on the load. This method is particularly important in situations where high-quality DC power is required, such as communication equipment and medical equipment.

NVVV brand uses efficient filtering technology in its 24vdc power supply products, which not only reduces the output harmonic content, but also improves the overall stability and reliability of the power supply.

Improving the performance of switching elements

Using high-performance switching elements is another effective way to reduce harmonic generation. In modern SMPS designs, high-frequency, high-efficiency MOSFETs or IGBTs are widely used. These elements can switch at a faster speed, thereby reducing switching losses and harmonic generation.

High-speed switching elements: High-speed switching elements can complete the on and off operations in a shorter time, reducing the current fluctuations during the switching process, thereby reducing the generation of high-frequency harmonics. The use of these elements can significantly improve the working efficiency of SMPS while reducing the interference of harmonics on the system.

Soft switching technology: Soft switching technology is a new technology developed in recent years. By reducing the rate of change of voltage and current (dv/dt and di/dt) at the switching moment, it reduces switching losses and reduces the generation of harmonics. Soft switching technology is commonly found in ZVS (zero voltage switching) and ZCS (zero current switching) circuits, which can further improve system efficiency while reducing EMI.

NVVV brand 24VDC power supply products use advanced high-frequency switching technology and soft switching design, which not only improves the efficiency of the product, but also effectively controls the generation of harmonics, making these power supply products widely used in various industrial and communication equipment.

Circuit layout optimization

The circuit layout of SMPS also has an important impact on the generation of harmonics. By optimizing the circuit layout, the coupling and propagation of switching noise can be effectively reduced, thereby reducing the amplitude of harmonics.

Compact PCB design: By arranging high-frequency switching components and related filters closely on the PCB, the effects of parasitic inductance and capacitance can be reduced, thereby reducing the amplitude of switching noise and harmonics. When designing, the key traces should be as short as possible and the ground layer should be complete to reduce the propagation of electromagnetic interference.

Layered design: In multi-layer PCB design, reasonable layering can further reduce signal interference. For example, isolating the switching circuit from the control circuit on different layers, or using a shielding layer to protect sensitive circuits can reduce electromagnetic interference and reduce the impact of harmonics.

NVVV brand uses a well-designed PCB layout in its SMPS products to ensure the best performance of each circuit module and effectively control harmonic interference. This design approach not only improves the reliability of the product, but also enables these power supplies to operate stably in complex power environments.

Use active harmonic compensation technology

In addition to traditional filters and circuit optimization, modern SMPS can also use active harmonic compensation technology (Active Harmonic Compensation, AHC) to further reduce harmonics.

Active filter: An active filter is an active compensation device that can detect and eliminate harmonic components in the power system in real time. Unlike passive filters, active filters generate currents opposite to harmonics through feedback control circuits to offset harmonics and improve power quality.

Harmonic suppression control algorithm: By introducing a harmonic suppression algorithm in the control circuit of the SMPS, harmonics can be compensated before they are generated. Such an algorithm can adjust the working state of the switching elements in real time, reduce harmonic generation, and optimize the overall performance of the system.

NVVV brand SMPS products have introduced advanced harmonic suppression technology, which not only reduces the impact of harmonics on the system, but also improves the overall stability and efficiency of the product. These technologies make NVVV's 24VDC power supply perform well in industrial control and communication equipment, becoming a leading product in the market.

Conclusion

As an important part of modern power conversion equipment, the switching power supply (SMPS) is widely used in various electronic devices due to its high efficiency, small size and strong adaptability. However, SMPS will inevitably generate harmonics during operation, which may interfere with the power system and other equipment. By understanding the working principle of SMPS and the mechanism of harmonic generation, we can take effective technical means, such as using filters, high-performance switching components, circuit layout optimization, and active harmonic compensation technology, to reduce the generation and impact of harmonics.

In this regard, NVVV brand SMPS products, with their excellent design and advanced technology, especially their 24VDC power supply products, have performed well in reducing harmonics and improving power quality. This has made NVVV's power supply solutions widely recognized and applied in industrial automation, communication equipment and other high-demand applications.

In future applications, with the increasing requirements for power quality and the continuous advancement of technology, SMPS will continue to play its irreplaceable role, and how to better control harmonics will become an important topic in product development and application. Through continuous innovation and optimization, we look forward to seeing more efficient and reliable power products provide more stable power support for our lives and work.