Noise (Immunity/EMS) type and How to protect?

1. Noise type

The noises which is applied to power supply coming from outside are shown below.

  1. Electrostatic discharge immunity
  2. Impulse noise, Electrical fast transient/burst immunity
  3. Surge immunity
  4. Conducted Disturbances, induced by radio-frequency fields
  5. Radiated, radio-frequency, electromagnetic field immunity

2. Countermeasures

(1) Countermeasures in power supply

Basically, countermeasures for EMI could be effective for noise immunity as well. Therefore, various countermeasures for EMI play key role for noise immunity.
The following countermeasures are taken in power supply.

  1. Built-in input filter.
  2. Optimized FG line in design of printed-circuit board and chassis.
  3. Adopt noise countermeasure component, such as ferrite core, differential-mode choke.

(2) Countermeasures in user's system

EMC directive is generally applied to the end use product. Therefore, the following countermeasures should be taken to the whole system as well as power supply.

  1. External filter / Surge absorber
    Setting a surge absorber or a filter for tolerating impulse noise at AC terminal of the unit will be effective to reduce high-voltage noise.
  2. Wiring of input line / output line
    The input line and the output line should be separated to avoid spoiling an effect of noise filter.
  3. Earthing wire
    Earth potential ideally is stabilized potential. However, depending on the way of wiring, impedance will be increased and it may cause failure of system due to conducted noise.
    Earthing wire should be avoided to curl long and be wired as thick and short as possible.

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