Explanation of external disturbances of switching power supplies
External interference to a switching power supply can exist in either "common mode" or "differential mode". The type of interference can vary from a short duration spike to a complete loss of power. It also includes voltage variations, frequency variations, waveform distortion, persistent noise or clutter, and transients.
The main thing that can be transmitted through the power supply and cause damage to the equipment or affect its work is the electrical fast transient pulse group and surge shock wave, while the electrostatic discharge and other interference as long as the power supply equipment itself does not produce vibration, output voltage drop and other phenomena, it will not result in the power supply caused by the impact on the power equipment.
Power conversion circuit: power conversion circuit is the core of the switching regulator power supply, it produces a wider band and harmonic rich. The main components that produce this pulse interference are:
1) switching tube switching tube and its heat sink and shell and power supply leads within the distribution capacitance, when the switching tube flows through a large pulse current (largely rectangular wave), the waveform contains many high-frequency components; at the same time, the switching power supply device parameters such as switching power tubes, such as storage time, the output stage of the large current, switching rectifier diode reverse recovery time, will cause an instantaneous short-circuit circuit, resulting in a very large Short-circuit current, in addition, the load of the switching tube is a high-frequency transformer or storage inductor, in the instant of switching tube conduction, the transformer primary appears to be a large inrush current, resulting in spike noise.
2) high-frequency transformer switching power supply transformer, used as isolation and transformer, but due to leakage inductance, will produce electromagnetic induction noise; at the same time, in the high-frequency condition of the transformer layer of the distributed capacitance will be the primary side of the high-harmonic noise to the secondary side, and the transformer to the shell of the distributed capacitance to form another high-frequency path, so that the electromagnetic field generated around the transformer is more likely to be coupled to the other lead to the formation of noise.
3) rectifier diode secondary side rectifier diode used as a high-frequency rectifier, due to the factor of reverse recovery time, often forward current accumulation of charge in the addition of reverse voltage can not be immediately eliminated (due to the presence of carriers, there is a current flow). Once this reverse current recovery when the slope is too large, flow through the coil inductance produced a spike voltage, in the transformer leakage inductance and other distribution parameters will produce a strong high-frequency interference, the frequency of which can reach tens of MHz.
4) Capacitors, inductors and wires switching power supply due to work at a higher frequency, will make the low-frequency component characteristics change, which produces noise.
