How to quickly find out the problem of switching power supply?
inductor
Switching power supplies use low EMI inductors with closed ferrite cores. Such as round or closed E-cores. Open cores can also be used if they have lower EMI characteristics and are kept away from low power wires and components. If using an open core, it is also a good idea to have the poles of the core perpendicular to the PCB. Rod cores are usually used to eliminate most of the unwanted noise.
Feedback
Try to keep the feedback loop away from inductors and noise sources. Also make the feedback line as straight as possible and thicker. There is sometimes a tradeoff between these two approaches, but keeping the feedback line away from the inductor's EMI and other noise sources is the more critical of the two. Place the feedback line on the side opposite the inductor on the PCB and separate it with a ground plane in the middle.
filter capacitor
When using a small ceramic input filter capacitor, it should be placed as close as possible to the VIN pin of the IC. This will remove as much of the effect of line inductance as possible, giving the internal IC lines a cleaner voltage source. Some designs of switching power supplies require the use of a feed-forward capacitor connected from the output to the feedback pin, usually for stability reasons. In this case, it should also be located as close as possible to the IC. Using surface mount capacitors also reduces lead length, which reduces noise coupling into the effective antenna due to through-hole components
compensate
If it is necessary to add external compensation components for stability, they should also be as close as possible to the IC. Surface-mount components are also recommended here for the same reasons discussed for filter capacitors. These components should also not be too close to the inductor.
traces and ground plane
Keep all power (high current) traces as short, straight, and thick as possible. On a standard PCB, it is best to have an absolute minimum width of 15mil (0.381mm) per amp. The inductor, output capacitor, and output diode should be as close together as possible. This can help reduce EMI caused by switching power supply traces when large switching currents flow through them. This also reduces lead inductance and resistance, which reduces noise spikes, ringing and resistive losses, which can create voltage errors. The IC's ground, input capacitor, output capacitor, and output diode (if present) should all be connected directly to one ground plane. It is best to have a ground plane on both sides of the PCB. This reduces ground loop errors and absorbs more EMI generated by the inductor, thereby reducing noise. For multilayer boards with more than two layers, a ground plane can be used to separate the power plane (the area where the power traces and components reside) and the signal plane (the area where the feedback and compensation components reside) to improve performance. On multilayer boards, vias are required to connect traces to different planes. If the trace needs to carry a large current from one side to the other, it is good practice to use one standard via per 200mA of current.
Arrange the components so that the first current loops rotate in the same direction. There are two power states depending on how the head regulator is operating. One state is when the opening is closed and the other state is when the opening is open. During each state, a current loop is created by the power device that is currently on. The power devices are arranged so that the current loop conducts in the same direction during each state. This prevents magnetic field reversals in the traces between the two half-rings and reduces EMI emissions.
cooling
When using surface mount power ICs or external power switches, the PCB can often be used as a heat sink. This is to use the copper clad surface on the PCB to help the device dissipate heat. Refer to the specific device handbook for information on using PCB thermal dissipation. This can usually save the cooling device added by the switching power supply.
