Feedthrough capacitors are essential in suppressing high-frequency noise and electromagnetic interference (EMI) in electrical and electronic systems. Whether used in power lines, shielded enclosures, or critical control systems, selecting the right feedthrough capacitor ensures system stability and compliance with EMI standards.
This article explores the key factors to consider when choosing a feedthrough capacitor for your specific application.
1. Capacitance Value
• Noise Filtering Effectiveness
The capacitance determines how well the capacitor can suppress noise across different frequency bands. Higher capacitance values typically provide better attenuation at lower frequencies due to lower impedance.
• Application Match
For broadband EMI suppression, a higher capacitance might be necessary, while for targeted high-frequency filtering, a lower value with appropriate resonance characteristics could be more efficient.
2. Voltage Rating
• Safety Margin Is Key
Always choose a voltage rating that comfortably exceeds your circuit’s maximum operating voltage—typically by 20% to 50%. This prevents failures caused by voltage spikes or surges.
• Long-Term Reliability
Underrated capacitors are more prone to dielectric breakdown, leading to reduced lifespan or catastrophic failure.
3. Current Handling Capability
• Thermal Stress Consideration
The capacitor must safely carry the expected load current without overheating. Excessive current can lead to resistive heating, degrading internal materials.
• Verify RMS and Peak Load
For AC applications, both the RMS current and peak transient currents should be accounted for, especially in switching power supplies or motor drive systems.
4. Frequency Characteristics
• Self-Resonant Frequency Matters
Every capacitor has a self-resonant frequency (SRF)—the frequency at which its impedance is lowest and filtering is most effective. Select a capacitor whose SRF is above the frequency range you need to filter.
• Tailored EMI Suppression
For best results, match the capacitor’s frequency profile to the EMI spectrum of your circuit.
5. Temperature and Environmental Stability
• Operating Range Compatibility
Ensure the capacitor’s rated temperature range aligns with your environmental conditions. Industrial and outdoor environments may require wide-range components.
• Low Drift Preferred
Capacitors with stable dielectric materials (like C0G or NP0 ceramics) offer minimal drift in capacitance over temperature.
6. Mounting Method and Layout
• Choose the Right Type
Feedthrough capacitors are available in solder-in, bolt-in, and screw-terminal types. Your choice depends on the mechanical design, space constraints, and grounding strategy.
• Ground Path Optimization
Good grounding is essential for EMI suppression. Bolt-in types often provide superior mechanical and electrical grounding for shielded enclosures and panel filters.
• Layout Impacts Performance
Poor PCB layout or long leads can introduce parasitic inductance, undermining high-frequency filtering performance.
7. EMI Filtering Strategy
• Filter Configurations
Feedthrough capacitors can be used alone or in configurations like Pi filters (capacitor-inductor-capacitor) or T filters (inductor-capacitor-inductor), depending on the suppression level required.
• Filter Depth and Spectrum
In environments with high EMI levels—like industrial automation or military systems—a multi-stage filter may be required to meet emissions standards.
• Useful Insight
As noted by EMC Directory, feedthrough capacitors are most effective when used as part of a comprehensive EMI strategy, especially when signal integrity is a concern.
8. Minimize Parasitic Effects
• Low Inductance Design
Feedthrough capacitors are specifically designed with a coaxial structure to reduce parasitic inductance. Still, installation matters—excess lead length or poor grounding can reduce performance.
• Short, Direct Paths
Ensure that signal and ground paths are as short and direct as possible to preserve filtering efficiency.
• Design Consideration
Parasitics may not show in simulations but have major real-world effects—especially at frequencies above 10 MHz.
9. Application-Specific Needs
• Power Lines
Use high-voltage, high-current types with robust mechanical mounting.
• Medical and Telecom Equipment
Focus on leakage current, compact size, and precision filtering across GHz frequencies.
• Shielded Enclosures
Select capacitors with superior grounding and high attenuation ratings to preserve shielding effectiveness.
• Military and Aerospace
Require components that meet high reliability standards, thermal extremes, and low EMI emission levels.
For more information, please refer to our article
👉 What is the purpose of a feedthrough capacitor?
