Do you understand the management and control of EMI and EMC?

What is a high-frequency circuit? What is its role? For high-frequency circuits, how to control EMI and EMC management? From improving the cost parity of renewable energy to enabling each of us to have an affordable, always-on From online communication devices to powering and connecting the Internet of Things, high-efficiency power conversion and ubiquitous wireless connectivity will be two trends that will profoundly impact sustainability and living standards.

On the other hand, both present tougher challenges in ensuring equipment meets electromagnetic compatibility (EMC) regulations. They need to function properly in the target environment without interfering with other nearby devices. In addition, EMC regulations in major global markets are becoming increasingly stringent as high-speed switching and high-frequency RF equipment crowd out the electromagnetic environment. Looking ahead, innovative technologies such as connected cars are expected to further intensify competition, adding a safety-critical aspect to the EMC issues surrounding everyday consumer-grade electrical equipment.

wide bandgap effect

In the field of power conversion, wide-bandgap semiconductor technologies such as silicon carbide (SiC) and gallium nitride (GaN) are being commercialized to improve the performance of traditional silicon devices: conduction losses are lower, chip size can be reduced, and thus costs can be reduced, The breakdown voltage is higher, temperature performance is increased, and faster switching speeds allow the use of smaller smoothing and decoupling components.

However, while increased switching frequency enables greater power density and lower energy losses, picosecond switching edges can drive harmonics deep into the RF realm. New power devices will have much higher slew rates than traditional silicon devices: for example, to ensure reliable switching of SiC devices, their gate voltages must be between +15V and -3V compared to the 0-10V gate voltage of standard MOSFETs In addition, if a higher DC bus voltage is used to improve efficiency, the dV/dt across the transistor will also be high. For a switching frequency of about 1MHz, the magnitude of the associated harmonics can be troublesome even for frequencies up to several hundred MHz. To ensure compliance with EMC standards, these issues must be addressed.

At the same time, as application and usage trends continue to evolve and more and more devices inevitably coexist in adjacent areas, EMC regulations are becoming increasingly stringent. These wireless devices will increasingly include mobile devices, tablets and IoT infrastructure via cellular, WLAN, PAN, LPWAN or sub-GHz RF, GSM/CDMA, 2.4GHz or 5GHz Wi-Fi or 2.4 GHz Bluetooth® 5 and other various frequency bands enable network connectivity.

The latest EU EMC Directive 2014/30/EU provides a good example. Revised technical limits require reduced conducted and radiated emissions and improved immunity to demonstrate compliance. The EU's new legislative framework places greater emphasis on market surveillance in order to detect and exclude the sale of non-compliant products. Various technical specifications are cited in the EMC Directive 2014/30/EU, including EN 50121-4 for railway signaling equipment, 50121-5 for electrical equipment, EN 55014 for household electrical products and equipment, and EN 55022 for IT equipment and multimedia equipment and 55032 and other new files. Meeting these technical specifications is one aspect of demonstrating compliance, another is maintaining satisfactory documentation.

In North America, the US Federal Communications Commission (FCC) has set out EMC requirements in its Part 15 legislation. For light industrial and industrial applications, the international IEC 61000-6-3 and IEC 61000-6-4 EMC standards are used respectively.

Dealing with power supply noise

Therefore, as power system designs drive switching frequencies higher, driving noise signals into or near the ISM radio band, EMC compliance becomes increasingly important but more difficult to achieve. Historically, the typical noise spectrum of switching power converters containing conventional silicon IGBTs or MOSFETs has covered a frequency range of approximately 10kHz to 50MHz. Most of these are within the conducted emissions range (9kHz to 30MHz) specified by CISPR/CENELEC and FCC noise standards.

Conducted noise can exist as differential mode noise (also called normal mode) or common mode noise and couples between the power supply and power or signal lines. Differential mode noise is generated due to the intended operation of the equipment and follows the signal or power lines, while common mode noise is coupled between the signal or power lines and unintended conduction paths, such as chassis components or the ground.

Conducted noise is usually handled by inserting power line or signal filters containing capacitors and/or inductors. Typically, a capacitor is oriented toward a high-impedance circuit—perhaps a power source or a load—while an inductor is used to connect a low-impedance circuit. If both the source and load are high impedance, you can use a purely capacitive filter, or use a π filter to achieve a steeper frequency response.

Global standards bodies have developed passive filter specifications, such as the European EN 60939 specification based on IEC 60939, and UL 1283 or MIL-F-15733 for the United States. KEMET's filters comply with applicable standards and are available in a variety of configurations, including single- or three-phase, chassis-mounted, board-mounted or feedthrough filters, with current ratings from less than 1A to 2500A. There are also special filters for applications such as medical equipment or lighting equipment that must comply with the EN 55015 emission standard to be sold on the EU market.

Attenuate high frequency noise

North American standards and European standards classify interference signals with frequencies above 30MHz as radiated emissions. Major sources of radiation include electrical cables and poorly designed PCB traces. Engineers should always use best design practices, including keeping these cables and traces as short as possible and routing any traces carrying signal pairs closely together on the board. However, this approach does not always solve EMC challenges and we need to take additional measures to attenuate high-frequency noise signals.

Fundamentally, the strategy for dealing with radiated noise is to convert high-frequency noise energy into heat by applying magnetic losses. For example, running the cable through a ferrite core can attenuate high-frequency radiated EMI. Due to the self-inductance of the cable, the conductive core interacts with the magnetic field generated by the common-mode noise current and exhibits high impedance at high frequencies. Passing the cable through the core multiple times increases the noise attenuation at any given frequency. Differential mode currents and low-frequency signal currents produce the smallest magnetic flux and therefore have little attenuation.

Flexible shielding solutions

Other sources of high-frequency noise radiators, such as PCB traces, must be addressed in a different way, usually with some form of shielding. Grounded metal shields are effective but add cost and a small enclosure that may not provide enough space for the shield and its mechanical attachment and ground connection. If the noise problem is discovered late in the project, there may not be time to design such a component.

Flexible shielding materials made from high permeability magnetic materials provide a convenient and economical solution. This method is so widely recognized that, in fact, the method used to measure its electromagnetic properties has been standardized in IEC 62333. The aim of this standard is to ensure that panel manufacturers clearly demonstrate the performance of their products so that end users can achieve comparable results in practice.

Figure 1: The composition of suppressor panels combines energy-absorbing properties with flexibility.

Other mature applications include ESD protection, wireless charging and RFID range enhancement, as well as counteracting receiver sensitivity degradation by preventing reflected interference in multi-radio devices such as laptops and mobile devices. Flex Suppressor is available in several penetration levels, providing designers with effective options for a variety of noise frequencies. They include standard grades with a relative permeability of 60 and ultra-high permeability materials with a value of 130. There is also an ultra-low permeability version with a value of 20, which provides extremely high noise attenuation in the Wi-Fi frequency range.

Summarize

High-frequency noise sources and tighter regulations pose challenges to power supply designers trying to use wide-bandgap semiconductors in their latest designs. Ferrite cores and high permeability suppression materials are being developed to resist radiated noise at frequencies up to 1GHz and beyond. The above is the relevant analysis of high-frequency circuits, I hope it can help you.