What are the main sources of electromagnetic interference in the power adapter?

Issue Time:2019-05-14
I don't know if you really understand the power adapter. Do you know the main electromagnetic interference sources in the power adapter? I don't know if it's okay, let's take a look at the main electromagnetic interference source in the power adapter.

The electromagnetic interference sources in the power adapter mainly include switching devices, diodes and non-linear passive components; in the switching power supply, improper wiring of the printed circuit board is also a major factor causing electromagnetic interference. For the power adapter, the electromagnetic interference generated by the switching circuit is one of the main sources of interference for the switching power supply. The switching circuit is the core, mainly composed of a switching tube and a high frequency transformer. It produces du/dt with a large amplitude pulse, wide frequency band and rich harmonics. The main reasons for this pulse pulse interference are:

1. The switch tube load is the primary coil of the high frequency transformer and is an inductive load. At the moment when the switch is turned on, the primary coil flows through a large inrush current, and a high surge spike voltage appears at both ends of the primary coil; when the switch tube is disconnected, a part of the energy is caused by the leakage flux of the primary coil. Without being transferred from the primary coil to the secondary coil, this portion of the energy stored in the inductor will form a fading oscillation with a capacitor and a resistor in the collector collector circuit, superimposed on the turn-off voltage to form a turn-off voltage spike. This power supply voltage interruption produces the same magnetizing inrush current transient as when the primary coil is turned on. This noise is conducted to the input and output terminals, causing conducted interference, which may break through the switching transistor.

2. The high-frequency switching current loop formed by the primary coil of the pulse transformer, the switching tube and the filter capacitor may generate large space radiation and form radiation interference. If the capacitance of the capacitor is insufficient or the high-frequency characteristics are not good, the high-frequency impedance on the capacitor causes the high-frequency current to be conducted in differential mode to the AC power source to form conducted interference.

Electromagnetic interference generated by a diode rectifier circuit. The |dv/dt| of the reverse recovery current generated by the rectifier diode in the main circuit is much smaller than the |di/dt| of the reverse recovery current of the freewheeling diode. As a source of electromagnetic interference, the rectifying diode reverse recovery current forms a large interference intensity and a frequency bandwidth. The voltage jump generated by the rectifier diode is much smaller than the voltage jump generated when the power switch in the power supply is turned on and off. Therefore, it is also possible to study the rectification circuit as part of the electromagnetic interference coupling channel without considering the effects of |dv/dt| and |di/dt| produced by the rectifier diode. The relationship between dv/dt and load size. The dv/dt generated when the power switch is turned on and off is the main interference source of the switching power supply. Theoretical analysis and experiments show that the load increases, the value of |dv/dt| generated by shutdown increases, and the load change has little effect on the opening dv/dt. Due to the difference in |dv/dt| generated when turned on and off, the externally generated interference pulses are also different. These are the main sources of electromagnetic interference in the power adapter.

Shenzhen Lianyunda Electronics Co., Ltd. is a professional power adapter manufacturer. Quality is our survival fundamentals, selected parts, comprehensive compatibility, fine craftsmanship, full quality, repeated testing, long life and more stable quality.

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