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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