(1) Overview of switching power supply technology
1. What is a switching power supply?
Switch Mode Power Supply (SMPS for short), also known as switching power supply and switching converter, is a high-frequency power conversion device and a type of power supply. Its function is to convert a level of voltage into the voltage or current required by the user through different forms of architecture. The input of a switching power supply is mostly AC power (such as mains) or DC power, and the output is mostly equipment that requires DC power, such as a personal computer, and the switching power supply converts the voltage and current between the two. 【Baidu Encyclopedia】
The switching power supply is different from the linear power supply. Most of the switching transistors used by the switching power supply are switched between the fully open mode (saturation region) and the fully closed mode (cut-off region). These two modes have the characteristics of low dissipation. The conversion will have higher dissipation, but the time is very short, so it saves energy and generates less waste heat. Ideally, switching power supplies themselves consume no power. Voltage regulation is achieved by adjusting the turn-on and turn-off times of the transistors. On the contrary, in the process of generating the output voltage of the linear power supply, the transistor works in the amplification area and consumes power itself. The high conversion efficiency of the switching power supply is one of its major advantages, and because the switching power supply has a high operating frequency, a small-sized and light-weight transformer can be used, so the switching power supply is also smaller in size and lighter in weight than the linear power supply.
Switching power supply products are widely used in industrial automation control, military equipment, scientific research equipment, LED lighting, industrial control equipment, communication equipment, electrical equipment, instrumentation, medical equipment, semiconductor refrigeration and heating, air purifiers, electronic refrigerators, liquid crystal displays, LED Lamps, communication equipment, audio-visual products, security monitoring, LED light strips, computer cases, digital products and instruments and other fields. 【Baidu Encyclopedia】
2. Overview of switching power supply technology
At present, the power tubes in switching power supplies on the market mostly use bipolar transistors, and the switching frequency can reach tens of kilohertz; the switching frequency of switching power supplies using MOSFETs can reach hundreds of kilohertz. In order to increase the switching frequency, high-speed switching devices must be used. For power supplies with switching frequencies above MHz, a resonant circuit can be used, and this working method is called a resonant switching method.
It can greatly increase the switching speed, theoretically the switching loss is zero, and the noise is also very small, which is a way to increase the operating frequency of the switching power supply. A megahertz converter using a resonant switching method has been put into practical use. The technical pursuit and development trend of switching power supply can be summarized as the following four aspects.
2.1 Miniaturization, thinning, light weight, high frequency
The volume and weight of the switching power supply are mainly determined by the energy storage components (magnetic components and capacitors), so the miniaturization of the switching power supply is essentially to reduce the volume of the energy storage components as much as possible; within a certain range, the improvement of the switching frequency , not only can effectively reduce the size of capacitors, inductors and transformers, but also suppress interference and improve the dynamic performance of the system. Therefore, high frequency is the main development direction of switching power supply.
2.2 High reliability
Switching power supplies use tens of times fewer components than continuous duty power supplies, thus improving reliability. From the perspective of life, the life of devices such as electrolytic capacitors, optocouplers, and exhaust fans determines the life of the power supply. Therefore, it is necessary to focus on design, use as few devices as possible, and improve integration. This not only solves the problem of complex circuit and poor reliability, but also adds functions such as protection, simplifies the circuit, and improves the mean time between failures.
2.3 Low noise
One of the disadvantages of switching power supplies is that they are noisy. Simply pursuing high frequency will increase the noise. Using partial resonance conversion circuit technology, in principle, it can not only increase the frequency but also reduce the noise. Therefore, reducing noise influence as much as possible is another development direction of switching power supply.
2.4 Using computer-aided design and control
Using CAA and CDD technology to design the latest conversion topology and optimal parameters, so that the switching power supply has the simplest structure and the best working condition. Introducing microcomputer detection and control into the circuit can constitute a multi-functional monitoring system, which can detect, record and automatically alarm in real time.
The development of switching power supply has always been closely related to the development of semiconductor devices and magnetic components. The realization of high frequency requires corresponding high-speed semiconductor devices and high-frequency electromagnetic components with excellent performance.
