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Adapter Noise Resolution
Dec 06, 2018

1, circuit oscillation

The adapter output has a large low frequency stabilization. Mostly, the stability of the circuit is not enough. Theoretically, the frequency domain method/time domain method or the Laws criterion in the system control theory can be used for theoretical analysis. Now, computer simulation methods can be used to easily verify the stability of the circuit to avoid self-oscillation, and a variety of software can be used. For the circuit that has already been completed, the output filter capacitor or inductor can be increased, the signal feedback position can be changed, the integral capacitance of the PI adjustment can be increased, and the open-loop amplification factor can be improved.

2, adapter PCB design

Mainly caused by EMI noise, the RF noise adjusts the PI regulator to include disturbances in the output error signal. Mainly check whether the high frequency capacitor is too far away from the switching element, whether there is a large C-shaped surround wiring. The PCB line of the control circuit is shared by at least two points and the power circuit. PCB copper clad wire is not an ideal conductor. It can always be equivalent to an inductor or resistor. When the power current flows through the PCB line shared with the control loop, a voltage drop occurs on the PCB. When the nodes of the control circuit are dispersed in different positions. The voltage drop caused by the power current causes disturbance to the control network and makes the circuit emit noise. This appears to occur mostly on the power ground, and attention to single point grounding can be improved.

3, magnetic components

The magnetic material has the characteristics of magnetic to strain, and the enameled wire is also subjected to electric power in the leakage magnetic field. Under the joint action of these factors, local harmonic or 1/N frequency resonance occurs locally. Changing the switching frequency and magnetic component dip coating can be improved.

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