(Author: China Computer Newspaper, 2000 at 16:27 on November 17)
■ The power supply of the power supply is the heart of the computer, the quality of the quality is not only damaged by the motherboard, hard disk, but also shortens the normal service life of the computer. Of course, the price of a quality power must not be cheap, so some merchants often use cheap and power to deceive consumers, and some users don't know much about this, but the difference between the district dozens of dollars may cause it. The loss of thousands of dollars, this is indeed a little worthless, so pay special attention to whether the quality of the power supply is excellent in purchasing. Safety standards have made strict regulations in the start of user life and property safety, in terms of insulation and flame retardant and other aspects of raw materials. Products that meet the safety standards not only require the product itself in line with safety standards, but also require a relatively complete safety production system for the production manufacturers. In these standards, the VDE-0806 standards based on German 1EC-380 standards are most stringent. my country's national standards are GB4943-1995 "information technology equipment (including electrical equipment)." The power supply is guaranteed by the above standards. The power supply meets the safety standards of a certain country and obtains certificates issued by their statutory sectors, such as obtaining certificates issued by UL agencies, called acquisition UL certification. China's safety certification body is CCEE. Regardless of the safety certification of the country, strict regulations on the cramping distance, anti-electricity strength, leakage current, temperature and the like. The creepage distance requires that the climbing distance refers to the shortest distance between the two conductive devices measured by the insulating surface or between the conductive devices and the device interface. UL, CSA and VDE safety standards emphasize the safety requirements of creepage distance, which is to prevent device between devices or devices and ground to threaten personal safety. The requirements of the electrical strength are added between or between the AC input line or between the zero voltage is added to the alternating current 1500V or DC 2200V, the no breakdown or pull arc is qualified. The requirements of leakage currents UL and CSA require exposure, and non-charged metal parts should be connected to the earth. The measurement of the leakage current is to measure the leakage current through a 1.5 kΩ resistance between these parts and the earth. The leakage current of the switching power supply should not exceed 3.5 mA under 260V AC input. Temperature requirements The safety standards pay attention to the temperature requirements of the electrical appliances, while the material is required to have flame retardancy. For the switching power supply, the internal temperature should not exceed 65 ° C, if the ambient temperature is 25 ° C, the temperature of the power supply should be less than 90 ° C. Power from the safety standard does not have a direct adverse effect on the user when you start using it, but after a long time, due to the influence of moist air and dust, it may cause short circuits in the high pressure area, which is not only damaged by the power supply itself, but also serious Affect the grid, thereby adversely affecting other electrical appliances. Regarding electromagnetic interference, the standards of internationally universal standards include FCC-A (industrial standards), FCC-B (civil standards), and power supply should comply with civil standards. After the switching power supply is a direct flow of the power frequency AC, then the switch is changed to high frequency communication, and thereafter rectifies a power source that stabilizes DC, so there is a noise and switch waveform generated by the rectifier waveform of the power frequency power supply. The noise is manifested in the input side leakage as a conduction noise and radiation noise, and the leakage of the output side appears as a ripple. Electromagnetic interference is divided into conduction interference and radiation interference. The conduction interference is propagated through the power line, the frequency is 30MHz, and the audio band is mainly interfered. Since the computer switching power supply has a metal shell shield, it is mainly conducted interference. The size of the conduction interference is an important standard for measuring the quality of the computer. It includes two aspects: one is to prevent electromagnetic interference from the power grid through the electromagnetic interference generated by the power supply itself into the grid, affect the normal operation of the host system; second, prevent the host itself Electromagnetic interference enters the grid and affects other electrical appliances. We may have such experience in our daily work. When the microcomputer is turned on, the electrical appliances, sounds, such as TVs, sounds, etc., which are not used properly, which is the influence of conduction interference.
