Features of adapter EMI

　　Features of adapter EMI

　　As an energy conversion device working in a switching state, the adapter has a high rate of change of voltage and current, and the interference intensity is relatively large; the interference source is mainly concentrated in the power switching period and the radiator and high-level transformer connected to it, compared with the digital circuit The location of the interference source is relatively clear; the switching frequency is not high (from tens of kilohertz and several megahertz), and the main forms of interference are conduction interference and near-field interference; and the printed circuit board (PCB) traces are usually wired by hand, with Greater arbitrariness, which increases the difficulty of the extraction of PCB distribution parameters and the estimation of near-field interference.

　　Resistor

　　Resistance, the English name resistance, is usually abbreviated as R. It is a basic property of a conductor and is related to the size, material, and temperature of the conductor. Ohm's law says, I=U/R, then R=U/I, and the basic unit of resistance is ohm, which is referred to as ohm for short. It is represented by the Greek letter "Ω" and has such a definition: when a voltage of one volt is applied to a conductor, the resistance corresponding to one ampere of current is generated. The main function of the resistor is to block the flow of current. The common unit that ohm often expresses the resistance value of resistance is also kiloohm (kΩ) and megaohm (MΩ).

　　1. Types of European power adapter resistors

　　There are many types of resistors, which are usually divided into three categories: fixed resistors, variable resistors, and special resistors. Among electronic products, fixed resistors are the most widely used. The fixed resistors can be divided into many categories by their manufacturing materials, but the commonly used and common ones are RT-type carbon film resistors, RJ-type metal film resistors, RX-type wire-wound resistors, and chip resistors that have been widely used in recent years. The model naming is very regular, R stands for resistance, T-carbon film, J-metal, X-wire wound, which is the first letter of pinyin. In old-fashioned domestic electronic products, you can often see resistors coated with green paint on the outside, which are RT-type. The red resistor is of type RJ. In general old-fashioned electronic products, green resistors are mostly used. why? This involves the issue of product cost, because although metal film resistors have high accuracy and good temperature characteristics, the manufacturing cost is also high, while carbon film resistors are particularly inexpensive and can meet the requirements of civilian products.

　　Of course, resistors also have power. The most common one is the 1/8 watt "color ring carbon film resistor", which is the most used in electronic products and electronic production. Of course, in some miniature products, a 1/16 watt resistor is used, which is much smaller. Then there is the miniature chip resistor, which is a member of the chip component family.

　　Second, the identification of professional custom power adapter resistors

　　These directly marked resistors are easy to identify the specifications when they are newly purchased. However, when assembling electronic products, it is necessary to take into account that for the convenience of future maintenance, the labeling surface should be oriented where it is easy to see. Therefore, pay special attention when bending your feet. In manual assembly, this additional process is not a big problem, but the machines on the automatic production line are not that smart. Moreover, the resistor elements are getting smaller and smaller, and the directly marked marks are difficult to see. Therefore, the "color circle notation method" is commonly used internationally. In fact, "color ring resistance" occupies the mainstream position of resistor components. "Color ring resistance", as the name implies, is to use different color rings on the resistor to indicate the resistance specifications. Some are represented by 4 color circles, and some are represented by 5. Is there a difference? Yes it is. Four-ring resistors are generally carbon film resistors. Three color rings are used to represent the resistance value, and one color ring is used to represent the error. The 5-ring resistor is generally a metal film resistor. In order to better express the accuracy, 4 color rings are used to indicate the resistance value, and the other color ring also indicates the error.

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