Sources of interference in cars

The loads on the automotive electrical system are diverse, ranging from small impedance and large current resistive loads, to small current and high voltage pulse generation devices, and high-frequency oscillation signal sources, which are not only potential interference emissions to the outside The source is also a source of interference to in-vehicle electronics. In addition, due to the high maneuverability, the car may also be in various conceivable complex electromagnetic fields from low frequency to high frequency, and the resulting electromagnetic interference coupling will also affect the normal operation of the automotive electronic and electrical system. The voltage in the automotive electrical system can be summarized into the following categories: normal operating voltage, abnormal steady-state voltage, radio interference voltage, transient overvoltage and electrostatic discharge.

Electromagnetic compatibility design of automobile electrical appliances

The electromagnetic compatibility environment of automobile electrical appliances should be an environment where devices coexist and do not interfere with each other, which requires the system to have good EMI and EMS characteristics. The occurrence of electromagnetic interference that causes degradation or failure of electrical functions must have three elements at the same time: interference source, interference coupling path, and sensitive equipment. Suppressing interference sources, blocking coupling, and raising the immunity threshold of sensitive equipment are the fundamental measures to solve the electromagnetic compatibility problem.

1 Transmission and transmission path of electromagnetic interference

The occurrence of electromagnetic interference will inevitably involve the transmission of interference energy and propagation channels. There are two basic methods of interfering transmission: conduction and radiation. The radiation coupling is subdivided into: antenna-to-antenna coupling, field-to-line coupling and line-to-line coupling. For the propagation and coupling of interference, the following system methods should be adopted in the practice of automotive electrical engineering to improve EMC characteristics: filtering, shielding, grounding and wiring.

2 Electromagnetic compatibility design of interference sources and sensitive equipment

In the functional circuit of the program, check whether the electromagnetic compatibility index meets the requirements; if the requirements are not met at this time, the parameters can be achieved by modifying the parameters, such as adjusting the operating frequency of the digital controller, the rate of rise of the round pulse, or re Select components, etc. Secondly, the protection design, including filtering, shielding, grounding and lap design, and even adopt the improvement measures such as space-time isolation and frequency avoidance. Finally, do layout adjustment design, including the inspection of the overall layout, the inspection of the gap of the shield, the layout inspection of components and printed boards, etc. The EMC design of circuits and subsystems includes the following steps: component selection, circuit selection, filtering technology application, grounding design, shielding design, circuit layout and system layout planning.

Figure 1 Schematic diagram of the hardware structure of the car driving recorder

3ESD protection design

In order to eliminate the hazards of electrostatic discharge, the measures that can be taken are: establish a perfect shielding structure, discharge the static charge to the ground through a grounded metal shell; use a little ground to connect the internal circuit and the metal shell; increase such as silicon transients Fast protection components such as voltage absorption diodes (STVS) discharge high-voltage charges to ground; printed circuit board designs add protective ring bands to discharge the charge of the circuit board by hand to the ground through the shortest path.

Figure 2 switching Power Supply circuit

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