Analysis of the development overview, key technologies and future trends of switching power supplies

1. Development Overview

Switching Power Supply is known as high-efficiency and energy-saving Power Supply. It represents the development direction of regulated power supply and has become the mainstream product of regulated power supply. For different equipment applications, switching power supplies are divided into two categories: (1) medium and small power switching power supplies; (2) high power switching power supplies. Medium and low-power switching power supplies generally adopt the form of switching power supply modules; while high-power switching power supplies are generally made of discrete components or control modules. For the core unit of high-power switching power supply, the pulse width modulation (PWM) controller integrated circuit was first developed abroad in 1977, typical products such as MC3250, SG3524, UC3842: Since the 1990s, foreign countries have developed switching frequency up to 1MHz. High-speed PWM, PFM (pulse frequency modulation) chips, typical products such as UC3842, UC1864, etc.; for the monolithic integration of centering, 21, and power switching power supplies, there are roughly two stages: In the early 1980s, Yifa Semiconductor Co., Ltd. The company (SCS-Thomson) first introduced the L4960 series of monolithic switching regulators; in the 1990s, the company introduced the L4970A series. Its characteristic is to integrate the pulse width modulator, power output pole, protection circuit, etc. on a chip. It needs to be equipped with a power frequency transformer to isolate it from the power grid during use. It is suitable for making low-voltage output (5.1-40V), high and medium power (under 400W) ), high current (1.5-10A), high efficiency (over 90%) switching power supply, but in essence, it is still a C power converter for DC. In 1994, POWER first successfully developed a three-terminal isolated pulse-width modulation single-chip switching power supply in the world, which was called "top switching power supply". The first generation product is the TOPSwitch series, and the second generation product is the TOPSwitch-n series in 1997. In 1995, the company introduced a high-efficiency, low-power, and low-cost four-terminal single-chip switching power supply series; in 1999, Motorola introduced the MC33370 series of five-terminal single-chip switching power supplies, also known as high-voltage power switch regulators (HighvoltagePowerSwitchRegulator) . At present, single-chip switching power supplies have formed 4 series and nearly 70 models of products.

There are more than 300 independent R&D and manufacturers of domestic switching power supplies, and more than ten have formed scale. Some companies, such as the power supply series independently developed by China Power China Star, have been widely recognized, and have considerable advantages in the power supply market competition, and a small number of them have begun to export; the switching power supply developed by universities and colleges, such as Northwestern Polytechnical University, has certain technical advantages. , Among them, the high-performance communication switching power supply developed by Northwestern Polytechnical University is a better product.

2. The key technology of switching power supply
2.1 Working principle of switching power supply

Switching power supply mainly refers to the use of various new self-shutdown devices and high-frequency switching DC stabilized power supply made by conversion technology. There are many forms of it, among which pulse width modulation (PWM) is the most popular, and now I will focus on this form of switching power supply.

The principle structure of a switching power supply using PWM technology is shown in Figure 1. The energy is transferred from the power grid to the load. The AC voltage of the power frequency grid passes through the input rectifier filter circuit to obtain a high-ripple unregulated DC voltage, which is then transformed into a consistent The required rectangular wave pulsating voltage is finally smoothed into a continuous low-ripple DC voltage by the output rectifier filter circuit.

The control loop needs to complete the control of output voltage stabilization while providing high-voltage switch T tube base driving pulse, and it must also be able to provide protection for the power supply or load. It usually consists of basic circuits such as detection and comparison amplifier circuit, voltage-pulse width conversion circuit (V/W circuit), clock oscillation circuit, base drive circuit, overvoltage and overcurrent protection circuit, and self-use voltage source.

Known as a clock oscillator, this power supply uses a detection circuit to reflect the output voltage value, generates an error signal by comparing with a given reference voltage, and then modulates the pulse width by the V/W circuit to adjust the output voltage.

2.2 Key technology

(1). High frequency switching technology The higher the switching frequency of the power supply, the smaller the capacity of the transformer and filter capacitor required. This is the fundamental means to reduce the size and weight of the switching power supply. But increasing the switching frequency will increase the switching loss and the loss of passive components, as well as electromagnetic interference problems. Moreover, the higher the switching frequency, the higher the requirements for switching devices, which will reduce the reliability of the power supply and increase the power supply. the cost of.

(2). Soft switching technology

In order to solve the various adverse effects caused by increasing the switching frequency, soft switching technologies are usually used, including passive and lossless (absorption network) soft switching technologies, active soft switching technologies, such as ZVS/ZCS resonance, quasi-resonance, and constant frequency soft switching Technology (ZVS/ZCS-PWM), and zero voltage, zero current conversion (ZVT/ZCT-PWM) technology, etc. Since soft switching technology can effectively reduce switching loss and switching stress, and achieve the purpose of improving efficiency and increasing reliability, soft switching technology has been one of the research hotspots in the field of power electronics in recent years.

(3). Power factor correction technology

Increasing the input power factor of the switching power supply can reduce the reactive power loss of the power supply and reduce the harmonic pollution of the power supply to the power grid. Since switching power supplies are widely used in various fields, when a large number of switching power supplies are used simultaneously, it will have a serious impact on the power grid. Therefore, the use of power factor correction technology is the future development trend of switching power supplies, and the input power factor is an important parameter to measure the quality of switching power supplies.

(4). Intelligent technology

At present, foreign communication systems generally use centralized monitoring and distributed power supply (distributed households), and this power supply method is also being developed in China. The distributed power supply method has the advantages of high reliability, low cable loss, and strong failure tolerance. However, compared with the centralized power supply system, routine maintenance is inconvenient. Therefore, the use of intelligent technology to realize unattended operation can give full play to the advantages of the distributed power supply system and achieve obvious economic benefits. The intelligent technology of high-frequency switching power supply includes communication, fault diagnosis, control, etc., and intelligence is the development trend of high-frequency switching power supply.

3. The future trend of switching power supply
3.1 High frequency

High frequency is currently one of the main directions of the development of switching power supply technology, and it is also one of the main trends in the development of high-frequency switching rectifiers. But as the switching frequency increases, the switching loss of the power device will increase proportionally. Therefore, when the switching rate is relatively high, very effective "softening" measures must be taken to reduce the switching loss of the device as much as possible. At present, the more popular method is to use active soft switching technology, such as resonance technology, quasi-resonance (or multi-resonance) technology, ZCS-PWM (or ZVS-PWM) technology and ZCT-PWM (or ZVT-PWM) technology. Another more practical method is to use passive and lossless soft switching technology, that is, using passive devices (L, C, D, etc.) to form a unique (patented) circuit network to achieve lossless stepping for power switches.

3.2 Modularity

In addition to its strong adaptability, the modular structure has some important advantages, such as: low initial investment in the system, very convenient expansion, convenient installation and transportation, redundant work with little extra investment, and quick and convenient maintenance. At present, most communication power supply manufacturers adopt modular design, and have formed serialization. Their single rectifier modules

The current is mostly 5A, 10A, 30A, 50A, 100A, 200A, etc. In the field of communications, including mobile communications, the rectifier modules that are widely used are 30A, 50A, 100A, which can form DC systems of various power levels such as 150A, 300A, 600A, and 1000A, and are mainly used in large electronic telephone exchanges, mobile communication base stations, etc. .

3.3 Intelligent

Intelligentization is the inevitable result of the high standard requirements of modern communication systems for its basic power supply, and it is the perfect embodiment of the application of new SCM technology in the field of switching power supply. At present, most communication power supply manufacturers have successfully applied single chip microcomputer technology to high-frequency switch rectifier modules and monitoring modules, and connected to microcomputers through RS232, RS422 and other standard communication ports and MODEM to realize the "three remotes" function. Finally, through the public telephone network or the communication private network, the power system in different areas and even the world is connected to implement large-area centralized monitoring, which meets the high standards and high reliability requirements of modern communication systems, and achieves the purpose of intelligence .

3.4 Standardization

At present, the standards that high-frequency switching rectifier products need to meet when designing, in addition to their own specifications, mainly include electromagnetic compatibility standards and safety standards. Relevant international organizations and relevant domestic departments have actively formulated various electromagnetic compatibility standards, and various power supply manufacturers have already or are preparing their products to meet the requirements of these standards in order to achieve "green" products. Corresponding safety standards have been formulated at home and abroad, and various safety certifications have been implemented. For example, Europe has "CE" and logo certification, and China has "Great Wall" logo certification. Standardization is the need for product quality improvement and international development trends.

With the advancement of technology, especially the upgrading of power devices, the continuous improvement of power conversion technology, the continuous use of new electromagnetic materials, the continuous improvement of control methods, and the continuous development of related disciplines, switching power supplies have become a multi-disciplinary technical phase. The product of fusion.

At present, the communication high-frequency switching power supply produced in China is close to foreign products in function, but there is still a gap in performance, mainly in the lack of reliability and stability. The lack of systematic, modular, and engineering design methods and necessary simulation methods are the reasons why the system cannot work well. In short, the development direction of switching power supply is: (1) The frequency should be high, so that the dynamic response is fast, which is also necessary to cooperate with the high-speed microprocessor; (2) The volume should be reduced, and the transformer, inductance, and capacitor should be reduced in size; (3) The efficiency should be high, the heat generated is reduced, the heat dissipation is easy, and it is easy to achieve high power density, and then the ultra-high-power high-frequency switching power supply is manufactured; (4) The power system is highly integrated.

Best regards,

Ada Zheng