Filtering, Power Supply & Cable/Shielding
Once a failure is diagnosed, the fix usually comes from this module's toolkit: an LC filter tuned to the right corner frequency, correctly-sized common-mode and differential-mode components, a topology-aware layout, and disciplined cable shielding.
Drag the sliders to change the filter's inductance and capacitance and watch the insertion-loss curve (and corner frequency) update live.
A common-mode choke is wound so that differential current through the two windings cancels in the core (little differential impedance, so wanted power current passes freely), while common-mode current in both windings adds in the core (high common-mode impedance, blocking CM noise).
| Component | Targets | Placement Rule |
|---|---|---|
| X-capacitor | Differential mode | Directly across L-N, close to the noise source or the input connector |
| Y-capacitor | Common mode | From L/N to chassis/earth -- value limited by leakage-current safety requirements |
| Common-mode choke | Common mode | In-line on both conductors together, as close to the source of CM noise as practical |
| DM inductor | Differential mode | In series with each conductor individually |
Click a topology to see its typical CE failure mode and the layout discipline that keeps it clean.
- Terminate shields 360° at both ends where possible -- a "pigtail" connection defeats most of the shield's benefit at conducted-relevant frequencies.
- Keep noisy switching cables physically separated from quiet input/mains cables inside the enclosure.
- Twist differential pairs to reduce loop area and improve common-mode rejection.
- Bond shields to chassis at the point noise enters, not just at a single "convenient" ground point.
- Keep cable bundle length and height above any reference/ground plane consistent with the standard's test method, since it affects repeatability.
Module 9 Quiz
Select the best answer for each question. Instant feedback is provided after each response.