Typical Sources of Noise

especially radiated noise, can be reduced by understanding its sources and what design techniques can reduce its effects. There are several major 

Noise sources are part of noise loops which are printed circuit board connections between high-frequency current sinks and current sources. Following the PC board design practices in Section 3.14 will help greatly in reducing the radiated RFI. Appreciation of the high-frequency characteristics of the common components and PC boards is needed. 

Another major source of noise is the loop consisting of the output rectifiers, the output filter capacitor, and the transformer secondary windings. Once again, high-peak valued trapezoidal current waveforms flow between these components. The output Alter capacitor and rectifier also want to be located as physically close to the transformer as possible to minimize the radiated noise. This source also generates common-mode conducted noise mainly on the output lines of the power supply. 

One subtle, but major noise source is the output rectifier. The shape of the reverse recovery characteristic of the rectifiers has a direct affect on the noise generated within the supply. The abruptness or sharpness of the reverse recovery current waveform is often a major source of high-frequency noise. An abrupt recovery diode may need a snubber placed in parallel with it in order to lower its high-frequency spectral characteristics. A snubber will cost the designer in efficiency. Finding a soft recovery rectifier will definitely be an advantage in the design. 

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The variety of powered tools and equipment used on construction sites make many jobs easier, but at a price. That price is the noise they generate and the vibrations they set up in use. Typical sources of noise and vibrations include jack hammers, compactors, pneumatic drills, powered percussion tools, etc. The exhausts from internal combustion engines, whether in vehicles or stationary plant, adds to the level of noise. 

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