Adapter's noise solution

　　Noise comes from three aspects: PCB design, circuit oscillation and magnetic components:

　　1. Circuit oscillation

　　The adapter output has a great low-frequency wave stabilization. It is mostly caused by insufficient circuit stability margin. In theory, the frequency domain method/time domain method or the Routh criterion in the system control theory can be used for theoretical analysis. Now, computer simulation methods can be used to conveniently verify the stability of the circuit to avoid self-oscillation, and there are a variety of software available. For the circuit that has been completed, you can increase the output filter capacitor or inductance, change the signal feedback position, increase the integration capacitor of PI adjustment, and reduce the open-loop amplification.

　　2. Adapter PCB design

　　Mainly caused by EMI noise. RF noise adjusts the PI regulator to make the output error signal contain disturbances. Mainly check whether the high-frequency capacitor is too far away from the switching element, whether there is a large C-shaped surround wiring, etc.

　　There are at least two points on the PCB line of the control circuit shared with the power circuit. PCB copper-clad wire is not an ideal conductor, it can always be equivalent to an inductance or a resistor. When the power current flows through the PCB wire shared with the control loop, a voltage drop is generated on the PCB and the nodes of the control circuit are scattered in different positions. , The voltage drop caused by the power current disturbs the control network, causing the circuit to make noise. This appears to happen mostly on the power ground wire, pay attention to single point grounding can be improved.

　　3. Magnetic components

　　Magnetic materials have the characteristics of magnetism to strain, and the enameled wire will also be affected by electromotive force in the leakage magnetic field. Under the combined action of these factors, overtone or 1/N frequency resonance will occur locally. It can be improved by changing the switching frequency and dipping the magnetic components.https://powerstation-gf.com/prodcuts/SPS-001-wall-mounted-home-energy-storage_283.html

　　Noise sources

　　From the above analysis, we can know that there are many noise interference sources in the adapter, and there are various interference channels. The noise interference sources with greater impact can be summarized into the following three types:

　　1. The interference caused by the reverse recovery time of the diode.

　　2. Harmonic interference generated when the switch tube is working.

　　The power switch tube flows through a relatively large pulse current when it is turned on. During the cut-off period, the sudden change of current caused by the leakage inductance of the high-frequency transformer winding will also cause spike interference.

　　3. Interference caused by the AC input circuit of the camera power adapter.

　　The rectifier tube at the input end of the adapter will also cause high-frequency attenuation oscillations during the reverse recovery period. Generally, a relatively large filter capacitor is always connected to the back of the rectifier circuit, so the conduction angle of the rectifier tube is small, which will cause a large charging current, which will distort the AC current on the AC input side and affect the power supply quality of the power grid. In addition, the equivalent series inductance of the filter capacitor also has a greater impact on interference.

　　All these interferences can be divided into conduction interference and radiated interference according to the propagation path. The interference caused by the spike interference and harmonic interference energy generated by the adapter propagates through the input and output lines of the adapter is called conducted interference. When the energy of harmonics and parasitic oscillations propagate through input and output lines, electric and magnetic fields are generated in space. These interferences generated by electromagnetic radiation are called radiation interferences.

　　Because the adapter itself is a strong interference source, in addition to taking measures on the circuit to suppress its electromagnetic interference, the adapter should also be effectively shielded, filtered and grounded.

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