Do you know the usual types of interference from switching power supply? In general, it is divided into two categories, respectively, the interference formed by the internal components of the switching power supply; The interference caused by switching power supply due to the influence of external factors. Both involve human and natural factors.

I. Internal interference of switching power supply

The key to EMI caused by switching power supply is the high harmonic current interference caused by the basic ballast and the peak voltage interference caused by the output power conversion circuit.

There is a distributed capacitance between the switch tube and the heat pipe radiator and the lead wire inside the housing and power supply. When the switch tube passes through large pulse current (roughly rectangular frame wave), the wave pattern has a lot of high frequency components. At the same time, the components of main parameters such as power supply application switch power tube of storage time, big output power flow, switch rectifier diode reverse recovery time, can lead to a control circuit instantaneous short circuit, caused great short-circuit current, in addition, the load switch tube is a high frequency transformer or energy storage inductors, at the instant of the switch tube conduction, transformer primary large flow, lead to the peak noise.

2: the transformer in the high frequency transformer switching power supply, as protection and voltage change, but because of the reason of leakage, will cause electromagnetic induction noise; At the same time, in the case of high frequency, the distributed capacitance between the transformer layer will transmit the high-order harmonic noise of multiple side to the secondary, and the transformer forms another high-frequency loop for the distributed capacitance of the housing, so that the magnetic field caused by the transformer surrounding is more likely to be coupled to other leads to form noise.

3: rectifier diode again side rectifier diode as a high frequency rectifier, because of the reverse recovery time factor, so the positive charge of the forward current accumulation in the reverse voltage can not be immediately removed (because of the carrier in, there is current flow through). If the slope of this reverse current repair is too large, the inductor passing through the solenoils will create a spike voltage, which will cause extremely high frequency interference in the form of leakage inductance of the transformer and other major distribution parameters, with a frequency of more than 100 MHz.

4: Switching power supply of capacitor, inductor coil and power transmission line works at high frequency, which will make the characteristics of high frequency components change greatly, thus causing noise.

Two, external interference of switching power supply

Switching power supply external interference can be "common mode" or "differential mode" method exist. The type of interference can vary from very short spikes to complete loss of power. At a minimum, it also includes voltage transitions, frequency transitions, mode loss of frames, continuous noise or low-frequency oscillations and their transients.

Can be transmitted according to the power supply and lead to the destruction of the equipment or the key to affect its work is the rapid electric transient monopulse group and the surge shock wave, and electrostatic discharge and other interference if the power supply equipment itself does not cause vibration stop, output voltage drop and other problems, it is not easy to cause the power supply caused by the impact on the power consumption equipment.