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​1. What are possible reasons for severe heating of common mode inductors? How to troubleshoot?​
Answer: Possible reasons:

Excessive differential mode current: Common mode inductors have weak suppression capability for differential mode current. If differential mode current in the circuit exceeds design values, it increases copper loss (I²R) in windings, causing heating.
Core saturation: When common mode current or differential mode current is too high, magnetic flux density in the core exceeds saturation point, permeability drops sharply, and eddy current losses increase dramatically, causing core heating.
· Abnormal winding resistance: Winding wires are too thin, local short circuits or poor contact during winding.

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1. What fixture should be used for insertion loss testing of common mode inductors? Why?​
Answer: Insertion loss testing of common mode inductors typically uses 50Ω standard coaxial fixtures (such as BNC or SMA interface fixtures), and in some scenarios, they are used in conjunction with LINE IMPEDANCE STABILIZATION NETWORK (LISN). Reason: According to EMC testing standards (such as CISPR 16, IEC 61000-4-6), the characteristic impedance of the testing system needs to be unified to 50Ω.

​Question 1. How to optimize interference suppression above 10MHz through the combination of common mode inductors and Y capacitors?
Answer: Common mode inductors suppress interference through high common mode impedance from low to medium-high frequencies (e.g., below 1MHz), but at high frequencies (above 10MHz), impedance decreases due to parasitic capacitance (between windings, between windings and core), weakening suppression effect. Y capacitors (usually ceramic capacitors, such as MLCC) have low equivalent series resistance (ESR) and parasitic inductance (ESL), providing low impedance paths in high-frequency bands to divert common mode interference to ground. Optimization methods:
Capacitance selection:

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1. What is the optimal distance between common mode inductors and X capacitors? Why?​
Answer:
The optimal distance between common mode inductors and X capacitors is generally recommended to be controlled within 3-5cm. The reason is that common mode inductors mainly suppress common mode interference, while X capacitors mainly filter differential mode interference. The two need to work together to form an EMI filter.
If the distance is too far, parasitic inductance between leads increases, causing impedance matching of the filter network in high-frequency bands (e.g., above 100MHz) to be disrupted, and interference signals may "bypass" the filter through parasitic parameters...

1. What special parameter requirements do common mode inductors need to meet in 5G base station power supplies?​
Answer:
High-frequency response and low parasitic capacitance: Need to maintain high impedance (e.g., above 1000Ω) in frequency bands above 100MHz, parasitic capacitance needs to be <10pF to avoid high-frequency signal leakage.
High saturation current: Meet large current requirements of base station power supplies (e.g., above 10A). Core materials preferably nanocrystalline or iron silicon aluminum to balance saturation characteristics and high-frequency loss.
Wide temperature range: Operating temperature needs to cover -40°C to +85°C, some outdoor base stations require...

Point 1. What is the impedance difference between MnZn ferrite and NiZn ferrite common mode inductors at 30MHz frequency?
Answer: The permeability of MnZn ferrite can reach 5,000,
  but permeability may start to decline at 20kHz frequency. At 30MHz frequency, its permeability has decreased significantly, resulting in relatively low impedance.
  NiZn ferrite has low initial permeability but maintains permeability unchanged at high frequencies (100MHz). At 30MHz, it can maintain certain permeability, so impedance is relatively high. However, specific...

Question 1. How to calculate the saturation margin of common mode inductors based on the circuit's maximum surge current?
Answer: The saturation margin of common mode inductors is a key parameter to ensure they do not enter magnetic saturation under surge current. Calculation steps are as follows:
 
Key logic: Differential mode currents generate magnetic fluxes that cancel each other in common mode inductors, usually not causing saturation; while common mode surge currents superimpose magnetic flux, potentially saturating the core. Margin needs to be achieved through core material selection and increasing coil turns or magnetic circuit cross-sectional area.
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Question 2. What is the...