PCB Blog - About EMC design

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Why should we do EMC design for products?

Generally, it is to meet the functional requirements of the product Reduce the debugging time, and make the product meet the requirements of electromagnetic compatibility standards, so that the product will not produce electromagnetic interference to other equipment in the system.

How many aspects can we do EMC design for products?

Our EMC design mainly includes Circuit Design (including device selection) Circuit board design Shielding structure Signal line/power line filtering Design of circuit grounding mode, etc.

Basic principles of EMC Design:

Electronic circuit design criteria electronic circuit designers often only consider the function of the product without considering the function and electromagnetic compatibility. Therefore, when the product completes its function, it also produces a large number of functional harassment and other harassment. Moreover, the sensitivity requirements cannot be met. The EMC design of electronic circuits should consider the following aspects:

Component selection in most cases, the degree to which the basic components of the circuit meet the electromagnetic characteristics will determine the degree to which the functional unit and the final equipment meet the electromagnetic compatibility. The main criteria for selecting appropriate electromagnetic components include band characteristics and circuit assembly technology. Because whether EMC can be achieved is often determined by the response characteristics of components far away from the fundamental frequency. In many cases, circuit assembly determines the out-of-band response (such as lead length) and the degree of coupling between different circuit components. The specific rules are:

1. At high frequency, compared with lead-in capacitors, it should be better to filter with through-core capacitors or support capacitors with small lead inductance.

2. When lead-in capacitors must be used, the influence of lead-in inductance on filtering efficiency should be considered.

3. Aluminum electrolytic capacitors may have a temporary dielectric breakdown of several microseconds, so solid capacitors should be used in circuits with a large ripple or transient voltage.

4. Use resistors with small parasitic inductance and capacitance. Chip resistors can be used in the UHF band.

5. Large inductance has large parasitic capacitance. In order to improve the insertion loss of low-frequency parts, do not use a single section filter, but use a multi-section filter composed of several small inductors.

6. When using the core inductance, paying attention to the saturation characteristics, especially the high-level pulse will reduce the inductance of the core inductance and the insertion loss in the filter circuit.

7. Try to use shielded relays and ground the shielding shell.

8. Select effective shielding Isolated input transformer.

9. The power transformer used for sensitive circuits should have electrostatic shielding, and the shielding shell and transformer shell should be grounded.

10. Shielded wires must be used for interconnection signal wires inside the equipment to prevent disturbance coupling between them.

11. In order to connect each shield with its own pin, a plug base with enough pins should be selected.