Q&A(FAQ) Types of noise (Emission/EMI) and how to priotect?
1. Types of EMS
The noise applied to the power supply from external sources is shown below.
The types of external noise that may affect the power supply are as follows:
- i.Electrostatic discharge (ESD)
- ii.Impulse noise and electrical fast transient (EFT)/burst
- iii.Surge
- iv.Conducted disturbances induced by radio-frequency fields
- v.Radiated radio-frequency electromagnetic fields
2. Countermeasures for EMS
(1) Countermeasures in the power supply
In general, countermeasures for EMI are also effective for improving noise immunity. Therefore, various EMI countermeasures play a key role in enhancing noise immunity.
The following countermeasures are implemented in the power supply.
- i.Built-in input filter.
- ii.Optimization of the FG line in the design of the printed-circuit board and chassis.
- iii.Use of noise-suppression devices such as ferrite cores and differential-mode chokes.
(2) Countermeasures in the User’s System
The EMC directive generally applies to the end-use product. Therefore, the following countermeasures should be implemented not only in the power supply but also throughout the entire system.
- i.External Filter / Surge Absorber
Setting a surge absorber or a filter at the AC input terminal of the unit is effective in reducing high‑voltage impulse noise.
* When an EMI filter is used on the input line, and a surge voltage is applied, the input voltage may increase due to the energy stored in the choke coil of the EMI filter. Sufficient evaluation with the actual application is required to select a suitable EMI filter. - ii.Wiring of Input Line / Output Line
The input and output lines should be routed separately to avoid degrading the effectiveness of the noise filter. - iii.Earthing Wire
Ideally, the ground potential should be stable. However, depending on the wiring method, the impedance may increase and cause system failure or malfunction due to conducted noise.
The earthing wire should be as thick and as short as possible.