What are the 11 basic principles that should be followed in EMC design?
When designing electronic circuits, many engineers focus solely on functionality without considering electromagnetic compatibility (EMC). This oversight can lead to unwanted interference and failure to meet sensitivity requirements. To ensure proper EMC performance, designers must take a holistic approach from the beginning. The selection of components plays a crucial role in determining the overall electromagnetic behavior of a circuit. Key factors include out-of-band characteristics and assembly techniques, as these often dictate how well a circuit will perform in terms of noise immunity and emissions.
Here are the 11 key principles to consider during EMC design:
(1) At high frequencies, it is better to use feedthrough or pedestal capacitors with low lead inductance instead of traditional through-hole capacitors for filtering. These types of capacitors provide more effective noise suppression at higher frequencies.
(2) If through-hole capacitors are necessary, their lead inductance must be carefully considered, as it can significantly reduce filtering effectiveness, especially at higher frequencies.
(3) Aluminum electrolytic capacitors can experience temporary dielectric breakdown under high-voltage transients. Therefore, solid-state capacitors are recommended for circuits with large ripple currents or transient voltage spikes.
(4) In ultra-high frequency applications, chip resistors with low parasitic inductance and capacitance are preferred. These components help maintain signal integrity and reduce unwanted coupling.
(5) Large inductors tend to have significant parasitic capacitance, which can degrade performance at lower frequencies. To improve insertion loss, multi-section filters made from smaller inductors are more effective than single-section designs.
(6) When using core inductors, it's important to pay attention to saturation characteristics. High-level pulses can cause the inductor to saturate, reducing its inductance and insertion loss in filter circuits.
(7) Shielded relays should be used wherever possible, and their shields should be properly grounded to prevent radiated and conducted emissions.
(8) Input transformers must be effectively shielded and isolated to prevent noise from entering the sensitive parts of the circuit.
(9) Power transformers used in sensitive circuits should have electrostatic shielding. The shield housing and transformer casing should both be grounded to minimize coupling and interference.
(10) Internal signal lines within the equipment should always be shielded to prevent crosstalk and electromagnetic coupling between different circuits.
(11) Each shield should be connected to its own grounding pin. A connector with enough pins is essential to ensure reliable and effective shielding connections.
By following these 11 principles, designers can significantly improve the electromagnetic compatibility of their products, ensuring they operate reliably in real-world environments without causing or suffering from interference.
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