EMC technology application in switching 18650 battery 3.7v 2200mah

　　1 Generation and transmission of electromagnetic interference

　　There are two ways of electromagnetic interference transmission: one is conduction transmission, and the other is radiation transmission. Conducted transmission is a complete circuit connection between the interference source and sensitive equipment. The interference signal is transmitted along the connecting circuit to the receiver and electromagnetic interference occurs.

　　Radiated transmission is a form of interference in which interference signals propagate outward through a medium in the form of electromagnetic waves. There are three common types of radiation coupling: 1) The electromagnetic wave emitted by one antenna is accidentally received by another antenna, which is called antenna-to-antenna coupling; 2) The electromagnetic field in space is coupled through the induction of wires, which is called field-to-line coupling. 3) The coupling formed by the mutual induction of high-frequency signals between two equal wires is called line-to-line inductive coupling.

　　2 The generation mechanism of electromagnetic interference

　　From the perspective of the sensitive equipment being interfered with, interference coupling can be divided into conductive coupling and radiation coupling.

　　●Conduction coupling model

　　According to its principle, conductive coupling can be divided into three basic coupling modes: resistive coupling, capacitive coupling and inductive coupling.

　　●Radiation coupling model

　　Radiated coupling is another form of interference coupling. In addition to the intentional radiation emitted from the interference source, there is also a large amount of unintentional radiation. At the same time, the traces on the PCB board, whether they are power lines, signal lines, clock lines, data lines or control lines, can act as antennas, radiating interference waves and receiving them.

　　3Electromagnetic interference control technology

　　①Transmission channel suppression

　　●Filtering: When designing and selecting filters, attention should be paid to frequency characteristics, voltage resistance, rated current, impedance characteristics, shielding and reliability. Whether the filter is installed correctly or not has a great impact on its insertion loss characteristics. Only when the installation position is appropriate and the installation method is correct can the expected filtering effect on interference be achieved. When installing the filter, the installation location should be considered, the wiring on the input and output sides must be shielded and isolated, as well as the high-frequency grounding and bonding methods.

　　●Shielding: According to the principle, electromagnetic shielding can be divided into three types: electric field shielding, magnetic field shielding and electromagnetic field shielding. Electric field shielding includes electrostatic shielding and alternating electric field shielding; magnetic field shielding includes low-frequency magnetic field shielding and high-frequency magnetic field shielding. Different types of electromagnetic shielding have different requirements for shielding bodies. In actual shielding, the electromagnetic shielding effectiveness depends to a greater extent on the structure of the shield, that is, the continuity of conduction. Due to manufacturing, assembly, maintenance, heat dissipation, observation and interface connection requirements, actual shields generally have holes of different shapes and sizes. These holes play an important role in the shielding effectiveness of the shield. , so measures must be taken to suppress electromagnetic leakage from holes and gaps.

　　●Grounding: There are two types of grounding: safety grounding and signal grounding. At the same time, grounding will also introduce ground impedance and ground loop interference. Grounding technology includes the selection of grounding points, circuit combinations, grounding design, and the reasonable application of measures to suppress grounding interference.

　　●Overlapping: Overlapping is a low-impedance connection between conductors. Only good overlapping can enable the circuit to complete its designed function and enable various interference suppression measures to take effect. Overlapping methods can be divided into permanent overlapping and semi-permanent overlapping, while overlapping types are divided into direct overlapping and indirect overlapping.

　　●Wiring: Wiring is the key to the electromagnetic compatibility design of printed circuit boards. Reasonable wire widths should be selected and correct wiring strategies should be adopted, such as thickening the ground wire, closing the ground wire into a loop, reducing wire discontinuity, and using multiple Laminates, etc.

　　②Spatial separation

　　Spatial separation is an effective method to suppress space radiation harassment and inductive coupling harassment. By increasing the spatial distance between the harassment source and the receiver sensitive equipment, the intensity of the harassment electromagnetic field when it reaches the sensitive equipment has been attenuated to below the sensitivity threshold of the receiving equipment. , thereby achieving the purpose of suppressing electromagnetic interference. It can be known from the electromagnetic field theory that the field strength in the near-zone induced field is attenuated by 1/r3, and the field strength distribution of the far-zone radiation field is reduced by 1/r. Therefore, in order to meet the electromagnetic compatibility requirements of the system, try to increase the spatial distance between the various devices that make up the system. In equipment and system wiring, limit the minimum spacing of parallel cables to reduce crosstalk. In PCB design, the minimum spacing between lead strips is specified. In addition, spatial separation also includes the azimuth adjustment of the radiation direction of the harassment source and the control of the spatial orientation of the electric field vector and magnetic field vector of the harassment source when space is limited.

　　③Time separation

　　When the disturbance source is very strong and cannot be reliably suppressed by other methods, the time separation method is usually used so that the useful signal is transmitted within the time when the disturbance signal stops transmitting, or when a strong disturbance signal is transmitted, the sensitive equipment susceptible to harassment is short-lived. Always turn it off to avoid damage. There are two forms of time separation control. One is active time separation, which is suitable for situations where there is a definite sequence relationship between the appearance time of useful signals and the appearance time of interference signals; the other is passive time separation, which is based on the characteristics of interference signals and useful signals. One of the signals is quickly turned off to achieve the control requirements of non-overlapping time and non-coverage.

　　④Spectrum management

　　The planning and division of spectrum is to allocate each frequency band to various radio services and develop frequency bands for specific users. The development of national standards and specifications is the basis for preventing interference and, in some cases, ensuring that communication systems achieve the required communication performance. This includes the approval procedures for radio equipment and the documentation of minimum performance standards required for type approval of radio transmitters, receivers and other equipment.

　　⑤Electrical isolation

　　Electrical isolation is a reliable way to avoid conducted interference in a circuit while allowing useful signals to be properly coupled and transmitted. Common forms of electrical isolation coupling include mechanical coupling, electromagnetic coupling, photoelectric coupling, etc. DC/DC converter is a widely used electrical isolation device. It converts one DC voltage into another DC voltage. In order to prevent multiple devices from sharing a 18650 battery 3.7v 2200mah and causing interference from the internal resistance of the common 18650 battery 3.7v 2200mah, a DC/DC converter is used. Supply power to each channel separately to ensure that the circuit is not interfered by signals in the 18650 battery 3.7v 2200mah.

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