source:Industry News Popular:adapter release time:2022-03-23 09:17:07 Article author:sznbone
The power adapter is a power supply conversion device for small portable electronic equipment and electronic appliances. It is generally composed of shells, transformers, inductors, capacitors, control ICs, PCB boards and other components. Its working principle is to convert AC input to DC output; press the connection The way can be divided into wall type and desktop type. Widely used in security cameras, set-top boxes, routers, light bars, massagers and other equipment. The adapter is essentially a switching power supply, so the EMC problem has attracted more and more attention. Next, we will focus on analyzing the causes and treatment measures of radiation interference.
The test of radiated interference includes electric field emission and magnetic field emission, the electric field emission is produced by du/dt, and the magnetic field emission is produced by di/dt. Note: Spatial capacitance is a channel for electric field emissions, and common mode currents can generate considerable electric field emissions.
1. Electric field emission is mainly generated in the following parts:
(1) The primary and secondary voltage changes, in which the amplitude of the primary winding voltage change is large, which plays a leading role in the electric field emission.
(2) The magnetic core is also an electric field emission source.
2. Solution
Laying a copper sheet on the bottom layer of the PCB of the system or adding a copper sheet or a single panel at the forehead can effectively reduce the electric field emission and common mode current.
(2) Magnetic field emission
1. Magnetic field emission analysis 1
The loop with high di/dt generates magnetic field emission through the parasitic inductance of the loop, and the current on the secondary side changes with a large amplitude, which plays a leading role in the magnetic field emission.
Solution:
The parasitic inductance of a high di/dt loop increases with loop area, so magnetic field emissions are critical to PCB design. The current loop area on the secondary side should be as small as possible, and the wiring should be as short and thick as possible.
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