Electromagnetic Compatibility Research of Shenzhen PCB Design Company With the improvement of the performance of power semiconductor devices and the innovation of switching technology, power electronics technology has been widely applied to various power supply devices. The PCB design of the switching power supply is a crucial aspect to solve the electromagnetic compatibility problem of the switching power supply. Because it is responsible for the dual connection of the electrical components and mechanical components of the switching power supply, it is the key to reducing the EMI design of the electronic equipment.
1 Electromagnetic interference problems encountered by Shenzhen PCB design company
1.1 Electromagnetic coupling interference
In circuit design, electromagnetic coupling interference mainly affects other circuits through conduction coupling and common mode impedance coupling. From the perspective of EMC design, the switching power supply circuit is different from the ordinary digital circuit, and has relatively obvious interference sources and sensitive lines. In general, the interference source of the switching power supply is mainly concentrated on components and wires with large voltage and current change rates, such as power FETs, fast recovery diodes, high frequency transformers, and wires connected thereto. The sensitive line mainly refers to the control circuit and the line directly connected to the interference measuring device, because these interference coupling may directly affect the normal operation of the circuit and the interference level of the external transmission. Common mode impedance coupling is when the current of two circuits passes through a common impedance, and the voltage formed by one circuit's current on the common impedance affects the other circuit.
1.2 crosstalk interference
Crosstalk between lines, wires, and cables in printed circuit boards (PCBs) is one of the most difficult problems in printed circuit board wiring. The crosstalk mentioned here is a crosstalk in a broader sense, regardless of whether the source is a useful signal or noise, and the crosstalk is represented by the mutual capacitance and mutual inductance of the wires. For example, a strip line on the PCB carries control and logic levels, and a second strip line that is close to it carries a low level signal. When the parallel wiring length exceeds 10 cm, crosstalk interference is expected; Crosstalk interference also becomes a major issue when a long cable carries several sets of serial or parallel high speed data and remote lines. The crosstalk between the nearby wires and the cable is caused by the electric field passing through the mutual capacitance, and the magnetic field is caused by the mutual inductance.
When considering the problem of linear crosstalk on the PCB, the most important problem is to determine which of the electric field (mutual capacitance) and magnetic field (mutual inductance) coupling is more important. Determining which coupling model depends primarily on line impedance, frequency, and other factors. In general, capacitive coupling is dominant at high frequencies, but if one or both of the source or receiver is shielded and grounded across the shield, magnetic coupling will be dominant. In addition, there is generally a lower circuit impedance and inductive coupling at low frequencies.
1.3 Electromagnetic radiation interference
Radiated interference is interference introduced by the radiation of spatial electromagnetic waves. PCB electromagnetic radiation is divided into two types: differential mode radiation and common mode radiation. In most cases, the conducted interference generated by the switching power supply is dominated by common mode interference, and the radiated effect of common mode interference is much larger than that of differential mode interference. Therefore, reducing common mode interference is particularly important in the EMC design of switching power supplies. _)(^$RFSW#$%T
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