A simple analysis of the types of EMC filters

Under the same electromagnetic environment, using certain technical means to make various electronic technical means work normally without interfering with the normal operation of other devices is called electromagnetic compatibility (EMC).

The strict definition of electromagnetic compatibility in the national standard GB/T4365-1995 is that the equipment or system can operate normally in its electromagnetic environment without causing unbearable electromagnetic interference to anything in the environment.

Electromagnetic compatibility includes two aspects: electromagnetic interference (EMI) and electromagnetic endurance (EMS).

EMI refers to the interference and impact of electromagnetic waves caused by electromagnetic induction effects on surrounding electronic equipment; EMS refers to the ability of electrical products to prevent interference from external electromagnetic waves.

EMI includes: CE (conducted interference), RE (radiated interference), PT (interference power test), etc. EMS includes: ESD (electrostatic discharge), RS (radiation withstand), EFT/B (electrical fast transient burst), surge (lightning surge), CS (conducted disturbance), etc.

Classification of EMC filters

1. Reflective filter:

Composed of inductors and capacitors, it uses reflection or bypass to prevent interference signals from passing through.

2. Loss filter

Select materials with high loss coefficient or high loss angle tangent to convert high-frequency electromagnetic energy into thermal energy through eddy current.

For example: ferrite tube, ferrite magnetic ring, magnetic ring choke, etc.

3. Active filter:

Using active devices such as transistors can provide larger equivalent L and C values with smaller volume and weight.

Active Inductive Filter: Simulate the frequency characteristics of an inductive coil using transistors (the higher f, the greater the impedance).

Active capacitor filter: Use transistors to simulate the frequency characteristics of capacitors (the higher f, the smaller the impedance).

Cancellation filter (notch filter): It can generate current with the same amplitude and opposite phase (180 ° difference) as the interference signal to cancel the interference signal.