With the rapid development of computer and electronic technology, the application of electronic technology is becoming more and more extensive, and the types of electronic equipment are more and more. Electronic equipment is closely related to people's work and life. Any electronic equipment is inseparable from the reliable power supply, their power requirements are getting higher and higher. The miniaturization and low cost of electronic equipment make the power supply towards light, thin, small and efficient.
1.1. Development of Switching Power Supply
Switching power supply is divided into DC / DC and AC / DC two categories, the former output high quality DC, while the latter output high quality AC. The core of switch power is a power electronic converter, according to energy conversion type, can be divided into four kinds, the DC-DC converter is a DC can be converted into one or more DC power converter; inverter is the DC can be converted into one or more DC energy converter; rectifier is to convert AC to DC power converter, AC-AC converter.
By 1990s, the switching power supply has been widely used in the fields of electronics, electrical equipment and household appliances, and the switching power supply technology has entered a period of rapid development.
The switched-mode power supply uses a power semiconductor device as a switch to adjust the output voltage by controlling the duty cycle of the switch. In the case of a power transistor, the voltage drop across the collector and emitter is close to zero when the switch is saturated, and its collector current is zero when the switch is off. So its power is small, the efficiency can be as high as 70 to 95 percent, and the power is small, the radiator also decreases. Switching mode power supply directly to the grid rectifier, filter, adjust, and then by the switching regulator to regulate voltage, no power transformer. In addition, the switching frequency is tens of kilohertz, the filter capacitor and the inductor value is small, so the switching power supply has the advantages of light weight and small size. Finally, due to low power consumption, machine temperature rise, improve the stability and reliability of the machine, and its ability to adapt to the power grid has greatly improved, the general series power supply to allow power grid fluctuations range of 220V, and Switching type power supply in the grid voltage range of 110V-260V changes, can get a stable output voltage (Houyi Zhen. 2015).
The high frequency switching power supply is the development of the power technology innovation technology, the high frequency of the benefit is that small switching power supply device is unprecedented, and switching power supply into a wider field, especially in the high-tech fields, it promoted the small high-tech products, light switch, and development with the application of power supply has far-reaching significance in saving resources and protect the environment.
The 21st century, the market switching power supply in the power tube using bipolar transistor, the switching frequency up to tens of kilohertz; MOSFET switching power supply conversion frequency up to hundreds of kilohertz. To improve the switching frequency, high-speed switching devices must be used. For the megahertz switching frequency of the power supply can use resonant circuit, this work is called resonant switch mode, it can greatly improve the switching speed, the theoretical switching loss is zero, the noise is very small, which is a method to improve the switching power supply operating frequency. The megahertz converter with resonant switch mode has been put into practical use.
The development of switching power supply has always been associated with the development of semiconductor devices and magnetic components. The realization of high frequency requires the corresponding high speed semiconductor devices and high performance of high frequency electromagnetic components. Development of high-speed power MOSFET, IGBT and other new high-speed devices, the development of high-frequency low-loss magnetic materials used to improve the magnetic components of the structure and design methods to improve the filter capacitor dielectric constant and reduce its equivalent series resistance, it has always produced a huge role in promoting for switching power supply miniaturization. In short, in the switching power supply technology, in the study of low loss circuit technology, but also the development of new components, promote each other, and push switch power supply to more than two annual double-digit growth rate to a small, thin, high frequency, low noise and high reliability direction.