2018.06.21 Switching Noise - EMC
From here, we begin a new chapter on “Noise Countermeasures”. The countermeasures discussed here address noise in switching power supplies. However, the fundamentals and basic approach are applicable to electronic noise in general. In this first section of the new chapter we will explain “Procedures in Noise Countermeasures”.
Noise Countermeasures and the Product Development Phase
Prior to describing procedures in noise countermeasures, we shall first explain the noise countermeasures that should be taken at different stages, from product design and development through volume production.
The figure illustrates the fact that as development advances, the techniques and means that can be used to address noise become limited, and that the costs of countermeasures rise inexorably. If a noise problem is discovered only after mass production is begun, there are few options available; all that remains are highly undesirable measures such as modifying boards and the like.
As a basic rule, by conducting through studies and evaluations in the initial stage of product development, any noise problems that are discovered can be addressed with plenty of margin for error. It is also essential that noise types and properties be understood, and that effective countermeasures be employed for the respective types of noise. If measures are taken haphazardly, in many cases no effect may be observed, and the situation may even be worsened.
Procedures in Noise Countermeasures
As stated above, random countermeasures may merely worsen the problem. A number of procedures must be taken before a measure can be finalized. An example is presented below.
●Step 1: Ascertain the frequency components of the switching waveform
It is necessary to determine the frequency components of various phenomena that occur together with the fundamental wave--the switching frequency, rising and falling edges, overshoot/undershoot, ringing, and the like. This is because the countermeasures and components to be used will differ depending on the frequency of the noise that is to be addressed, and if appropriate methods and components are not selected, an improvement cannot be expected.
●Step 2: Ascertain the sources of the noise and the conduction paths
Determine the paths of conduction of the switching noise that is occurring on the primary side, or on the secondary side. Noise countermeasures must be implemented along the paths of noise conduction. Moreover, measures must be taken for all the conduction paths. If even one conduction path is overlooked, the countermeasure will be incomplete.
●Step 3: GND reinforcement
The final step in taking noise countermeasures is adding components to deal with the noise, but prior to this, reinforcement of the PCB (printed circuit board) ground should also be studied. A capable ground design is important not only for noise countermeasures, but for boosting performance and improving stability as well. Improved ground design can reduce loop impedance. Moreover, ground reinforcement is also effective for enhancing the effect of filters.
●Step 4: Add filters or other components to address the noise
Finally, components for dealing with noise are studied and are added to the circuit--filters for attenuation, bypass capacitors for noise bypass, chip beads and other resistive components to absorb noise, and so on, according to the type and properties of the noise. The effect of filters and bypass capacitors will differ according to the quality of the circuit ground, as explained in Step 3, and so ground reinforcement should always be performed beforehand.
・The further along product development advances, the more the techniques and means available to address noise are limited, and the more expensive the available options become.
・By conducting thorough studies and evaluations early in the product development stage, it is possible to implement noise countermeasures with a considerable margin for error.
・It is extremely important that noise types and properties be understood, and that measures suited to the respective noise types be implemented.
・Noise countermeasures are implemented through the procedures of first ascertaining frequency components, then grasping the sources and conduction paths of the noise, then reinforcing the circuit ground, and finally adding components to deal with the noise.