It is possible to reduce noise, especially radiated noise, by comprehending its causes and using appropriate design strategies. The majority of the conducted and radiated noise in a PWM switching power supply is produced by a few main noise sources. These sources are simple to identify, and we can change the design to lower the power supply's noise generation.
The loop between the current source and the high frequency current junction on the printed circuit board is one source of some of the noise. RFI radiation can be significantly decreased by using good PCB design practices. Understanding the high frequency properties of common components and PCBs is also essential.
The input power circuit, which includes the power switch, the primary winding of, is the first significant source of noise.
Another significant source of noise is the loop created by the secondary winding of the transformer, the output rectifier, and the output filter capacitor. Trapezoidal current waveforms with strong peaks also move between these components. To lessen radiated noise, the output filter capacitor and rectifier should also be installed as close to the transformer as practicable. On the grid power lines, this noise also produces common-mode conducted noise.
The output rectifier's reverse recovery procedure is a significant additional source of noise. Switching power supply noise generation is directly impacted by the rectifier's reverse recovery properties. The primary cause of high frequency noise on a waveform is typically abrupt reverse recovery currents. By joining an absorber in parallel, its high frequency spectral features can be muted.
