How to solve the EMI problem of voltage stabilizer noise in automotive system

Dealing with the Noise Radiation Problem of Switching Regulators

In automotive environments, switching regulators are typically used to replace linear regulators in areas that focus on heat dissipation and efficiency. In addition, switching regulators are typically the first active component of the input power bus, and therefore have a significant impact on the EMI performance of the entire converter circuit.

There are two types of EMI radiation: conduction type and radiation type. EMI This depends on the wires and circuit wiring connected to the product. Because noise is limited to specific terminals or connectors in the conceptual design, good layout or filter design as described above can often ensure compliance with conductive type EMI requirements at an early stage of the development process.

However, radiation EMI is another matter. All components on a circuit board that carry current radiate an electromagnetic field. Each wiring on the circuit board is an antenna, and each copper plane is a resonator. Except for pure sine waves or DC voltages, any signal can generate noise that covers the entire signal spectrum. Even after careful design, designers will never really know the radiation type until the system is tested. How serious can EMI be. And it is not possible to officially radiate until the design is basically completed. EMI testing.

Filters can attenuate intensity EMI at a certain frequency or over the entire frequency range. Part of the energy propagates through space (radiation), so metal and magnetic shielding can be added to attenuate it. Adding ferrite beads and other filters to a PCB can control the portion of the line (conduction). EMI cannot be completely eliminated, but can attenuate to an acceptable level for other communication and digital components. In addition, several regulatory agencies enforce standards to ensure compliance with required EMI requirements.

The performance of the new input filter module using surface mount technology is superior to that of the through hole module. However, this improvement is offset by an increase in the switching frequency of the switching regulator. Faster switching results in higher efficiency, shortest switching and off time, and thus higher harmonic weight. When all other parameters, such as switching capacity and switching time, remain unchanged, the switching frequency is doubled, and EMI worsens by 6 dB. Broadband EMI performance is like a first order high pass filter. If the switching frequency is increased by 10 times, it will increase dB radiation by 20 times.

In the field of electromagnetic compatibility, experienced PCB designers will design a very small thermal ring and keep the shielding layer as close to the source layer as possible. However, the device pin configuration, packaging structure, thermal design requirements, and the packaging size required to store sufficient energy in the decoupling assembly determine the minimum size of the thermal ring. A more complex problem is that in a typical planar printed circuit board, higher harmonic frequencies between lines above 30 MHz cancel out all filter efforts because the higher harmonic frequencies, the more effective the unwanted magnetic coupling.