In EMC design, selecting the correct feedthrough capacitor is half the battle. A wrong choice can not only lead to filtering failure but may also cause signal integrity issues. LCA has organized a clear and practical selection methodology to help you avoid common pitfalls and accurately identify the most suitable model.
Step 1: Define Key Parameters——Establish Selection Criteria
1.Working Voltage
Basic Requirement: Ensure the capacitor’s rated voltage exceeds the sum of the maximum DC bias and the peak AC ripple voltage in the circuit.
Safety Margin: It is recommended to leave a margin of at least 20%-30% to account for voltage surges and long-term reliability needs.
Pitfall Avoidance: Never apply the DC rated voltage directly to high-frequency AC circuits, as dielectric losses at high frequencies can lead to thermal failure.
2.Rated Current
Steady-State Current: Select a model capable of continuously handling the maximum steady-state current in the circuit.
Pulse Current: If the circuit experiences high pulse currents, additional consideration for the capacitor’s pulse current withstand capability is required.
Pitfall Avoidance: Neglecting current ratings can cause the capacitor to overheat, leading to performance degradation or permanent damage. Power line applications are key scenarios for rigorous current requirement checks.
3.Target Filtering Frequency Band
Low-Frequency Interference (<100 MHz): Typically requires higher capacitance values (e.g., 1000pF to 0.1μF) to provide a low-impedance path.
High-Frequency Interference (>100 MHz): Low Equivalent Series Inductance (ESL) is crucial. Here, the structural advantage of the feedthrough capacitor far outweighs the capacitance value itself. Choose a model with moderate capacitance but extremely low ESL.
Pitfall Avoidance: Using a capacitor with too high a capacitance value in a high-frequency circuit can be counterproductive. Its self-resonant frequency might fall within the interference band, potentially amplifying noise.
Step 2: Choose the Mounting Style——Match the Physical Design
1.Soldered
Applicable Scenarios: Metal panels or shielded enclosures where the highest shielding effectiveness and mechanical strength are required.
Advantages: Lowest ground impedance and best shielding effect.
Considerations: Strict control of soldering temperature and time is necessary; refer to our provided soldering process guide.
- Threaded
Applicable Scenarios: Interfaces requiring frequent plugging/unplugging or maintenance.
Advantages: Easy installation and reusability.
Considerations: Ensure the panel thickness matches the thread specifications and apply sufficient torque to guarantee a good ground connection.
Correct selection is a balancing act, requiring the optimal compromise between electrical performance, physical structure, and cost. By following the steps above, you can systematically avoid common errors and select the most suitable “Electromagnetic Guardian” for your design.
——2020.8.17
