Procedures in Noise Countermeasures

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 on the right describes the freedom of noise countermeasures, that is, the number of different countermeasure options available, as well as the costs incurred in deploying these countermeasures, plotted along the time axis that extends through design/development, evaluation, and mass production. The higher a curve is along the vertical axis, the more freedom there is, and the higher are the costs incurred.

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.