Switching power supply noise generation and suppression
First, the generation of power module noise
The topology of the flyback switching power supply is shown in Figure 1. The FET Q1 is turned on, the input current flows through the transformer and the FET Q1, and the FET Q1 is turned off, so that the input current is electromagnetically induced to the output end of the transformer to realize energy transfer. Due to the leakage inductance in the primary of the transformer, the leakage inductance and the parasitic capacitance of the FET Q1 oscillate, and the decompression spike generated by the oscillation is also transmitted to the output end during the energy transfer to form noise. The voltage waveform of the drain source stage is shown in Figure 2.
Figure 1 Flyback Power Topology
Figure 2 FET drain voltage waveform
Second, a good layout design to suppress noise
In the design process, engineers will add absorption circuits at both ends of the FET DS to reduce spikes and effectively reduce the output noise of the power module.
In practical applications, adding a capacitor to the input and output of the module, combined with a good PCB layout, can further reduce the output ripple and noise of the module. The layout of the PCB board, according to the current flow of the discharge capacitor, the power module ripple noise is no longer a problem. The figure below shows two layouts.
Figure 3 Correct Filter Capacitor PCB Board Layout
Figure 4 Wrong filter capacitor PCB layout
Zhou Ligong Zhiyuan Electronics developed the E_URBD-6W series module power supply design, considering the capacitance and transformer layout, effectively reducing the power module output ripple noise. The figure below shows the output ripple noise of the typical model E2405URBD-6W.
Figure 5 Excellent ripple noise
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hard copper wire
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