Switched-Mode Power Supply (SMPS) is widely used in modern electronic devices. Due to its high efficiency, small size and light weight, it has become the core power supply device of almost all modern electronic devices. Although it has become an indispensable part of daily life, many people are still unclear about the working principle of switching power supply and how it is different from traditional linear power supply. This article will delve into the basic principle of switching power supply and explain the technical details behind its efficient operation.

1. How does a switching power supply work?

The basic principle of switching power supply is based on regulating voltage and current by switching high-speed switching elements between on and off. In this way, the switching power supply can efficiently convert the input power into a stable output voltage and current. Unlike traditional linear power supplies, switching power supplies achieve power regulation through high-frequency switching and pulse width modulation (PWM) technology, which can maintain high efficiency over a wider range.

Input rectification and filtering

The first step of a switching mode power supply is to convert the input alternating current (AC) into direct current (DC). This is usually achieved through a rectifier circuit. The rectifier circuit contains multiple diodes, which can convert the positive and negative waves of the AC voltage into pulsating DC in a single direction.
However, the rectified DC power is not smooth, it still contains some ripples and noise. Therefore, the next step is to add a filter to smooth the current waveform, reduce the fluctuations in the voltage, and make the output current more stable.

High-frequency switching

The core part of the switching power supply is the high-frequency switching part. Here, high-speed switching transistors (such as MOSFET or IGBT) are used to achieve the conversion of electrical energy. These switching elements can switch at very high frequencies (usually tens of kilohertz or even hundreds of kilohertz). When the transistor is in the "on" state, the current passes, and when it is in the "off" state, the current is cut off.
The advantage of this high-frequency switching is that it can greatly reduce power loss. Compared with traditional linear power supplies, switching power supplies do not need to consume excess energy by adjusting resistors or through transformers. High-frequency switching can quickly convert voltage, and there is almost no excessive power loss between the "on" and "off" of the switch.

Transformation and isolation

The switched mode power supply also uses a transformer to adjust the output voltage. The DC power after the high-frequency switching operation is transmitted to the transformer, which adjusts the voltage according to demand and isolates the input and output. The role of this isolation is to ensure the safety of the equipment and prevent high voltage from directly acting on the terminal equipment.
Another advantage of the transformer is that it can convert high voltage to low voltage, or convert low voltage to high voltage. Through this voltage conversion, the switching power supply can adapt to the needs of different devices and ensure that each device receives the appropriate operating voltage.

Output Rectification and Filtering

After adjusting the voltage through the transformer, the current still needs to pass through the rectification and filtering circuit to ensure the smoothness of the output voltage and current. Similar to the input stage, the rectification circuit converts the pulse signal after high-frequency switching into direct current, and then further reduces the ripple through the filter.
Finally, the current after rectification and filtering becomes a stable direct current that can safely power electronic devices.

2. Why is the switching power supply so efficient?

Compared with traditional linear power supplies, one of the biggest advantages of switching power supplies is high efficiency. Linear power supplies usually rely on consuming excess power to achieve voltage regulation, while switching power supplies achieve efficient energy conversion through high-frequency switching and adjusting load current. So, what makes switching power supplies so efficient?

Differences in energy conversion methods

Linear power supplies adjust voltage by changing resistance or through a voltage regulator. This means that when the voltage difference is large, the linear power supply needs to consume a lot of energy to achieve a stable output voltage. Energy is wasted in the form of heat, so linear power supplies are generally less efficient.
Switching power supplies are different. It uses high-speed switching elements to switch the input high voltage to a low voltage suitable for the device, while consuming almost no excess power. This control method through pulse width modulation allows the switching power supply to adjust the voltage over a wide range with minimal energy loss.

High-frequency switching reduces transformer losses

In switching power supplies, the size and weight required for the transformer are also greatly reduced due to the presence of high-frequency switching. This is because at high frequencies, the transformer works more efficiently and can handle the same amount of current in a smaller volume.
In contrast, the transformer in a linear power supply often needs to be larger and heavier to handle the same power demand, which not only increases energy loss, but also takes up more physical space.

Low standby power consumption

Another significant advantage of switching power supplies is their low standby power consumption. When the device is in standby or low load state, the switching power supply can reduce energy consumption by reducing the switching frequency. This allows the switching power supply to remain efficient even when the device is not in use.

3. What are the applications of switching power supplies?

The high efficiency, lightness and flexibility of switching power supplies make them widely used in various fields. Whether it is consumer electronics, industrial equipment, or automobiles and communication equipment, switching power supplies play a vital role. The following are several major application areas of switching power supplies.

Computers and servers

Switching power supplies are widely used in computers and servers. Computers and servers usually require high-power power supplies and have high requirements for the efficiency of power conversion. Through efficient energy conversion, switching power supplies can meet high power requirements while maintaining low energy loss. This not only helps the operating stability of the equipment, but also reduces the overall energy consumption of the server.

Communication equipment

Switching power supplies are also widely used in the communication field, such as routers, base stations, switches and other equipment. Communication equipment has high requirements for power supply stability, and the efficient regulation and stable output of switching power supplies can meet this demand. In addition, since communication equipment is usually in a continuous operation state, low-energy switching power supplies can also help save a lot of electricity costs.

Consumer electronics

Many portable consumer electronic products, such as mobile phones, laptops, power tools, etc., are powered by switching power supplies. They rely on the small size and high efficiency of switching power supplies to provide a continuous and stable power supply. The lightness of switching power supplies allows these devices to be designed to be more compact and portable.

Medical equipment and laboratory equipment

Since switching power supplies can provide stable, low-noise power output, they are also widely used in medical equipment and laboratory equipment. They can provide power support for precision instruments and equipment while maintaining efficient operation to ensure the accuracy and safety of the equipment.

4. How to choose a suitable switching power supply?

In practical applications, choosing a suitable switch mode power supply is crucial to ensure the normal operation of the equipment. The following are several key factors to consider when choosing a switching power supply.

Output power

When choosing a switching power supply, output power is one of the most important considerations. According to the power requirements of the equipment, choosing a suitable switching power supply can ensure the normal operation of the equipment. Too low power will cause the equipment to fail to start, and too high power may cause waste and safety hazards.

Input voltage range

The input voltage range of the switching power supply determines the power supply environment it can adapt to. In some unstable power supply environments, choosing a switching power supply that can adapt to a wide input voltage range can ensure that the equipment can operate normally under different conditions.

Efficiency and Heat Dissipation

High-efficiency switching power supplies not only reduce energy loss, but also reduce the need for heat dissipation. Heat dissipation is an important issue in the operation of switching power supplies, especially in high-power devices. Therefore, choosing a switching power supply with good heat dissipation design and high-efficiency energy conversion can improve the overall stability and service life of the system.

Size and Weight

For portable or space-limited devices, the size and weight of the switching power supply is a key factor. Since the switching power supply can provide higher energy output in a smaller volume, it is necessary to consider whether its size is suitable for the physical requirements of the device when selecting it.

Conclusion

Switching power supplies have become an indispensable part of modern electronic devices with their high efficiency, small size and light weight. It provides efficient and stable power output through multiple links such as high-frequency switching, pulse width modulation, rectification and filtering. Whether in consumer electronics, industrial equipment, medical equipment or communications, switching power supplies have demonstrated their excellent performance.
When selecting and using a switching power supply(SMPS), it is important to understand its working principle and its influencing factors (such as efficiency, output power, heat dissipation, etc.). By reasonably selecting the right switching power supply, users can ensure the normal operation of the equipment and maximize the overall efficiency of the system.