Source of interference on the car.
Load on vehicle electrical systems varied, both the small resistance, the resistance sexy high current loads, there are low current, high voltage pulse generating device, as well as high-frequency oscillator signal source,glue stick which not only is the potential interference of foreign launch source, but also on-board electronics interference.
In addition, due to the high mobility vehicle may also be obtained at all can imagine the complexity from low to high frequency electromagnetic field, the resulting coupling of electromagnetic interference will affect the automotive electronic and electrical systems up and running. Within the vehicle electric system voltage can be summarized in the following categories: normal operating voltage, abnormal steady-state voltage, radio interference voltage, transient over voltage and electrostatic discharge.
EMC design of automotive electronics.
EMC automotive electrical equipment should be a coexistence environment, without disturbing each other's environment, glue gun which requires the system have good EMI and EMS characteristics. Cause degradation or failure of electrical functions of the occurrence of electromagnetic interference must have three elements: the source of interference, interference coupling paths and sensitive equipment. Interference suppression, blocking coupling and improve the immunity of sensitive equipment threshold is to solve the fundamental problem of electromagnetic compatibility measures.
1, the transmission electromagnetic interference and transmission channels.
The occurrence of electromagnetic interference interference inherent in the spread and transmission of energy channels. Interfere with the transmission, there are two basic ways: conduction and radiation. Radiation coupling broken down into: the antenna of the antenna coupling, the coupling field on the line and line to line coupling. For transmission and coupling means interference in the automotive electrical engineering practice, we should take the following approach to improve the EMC characteristics of the system: filtering, shielding, grounding and wiring.
2 interference source and sensitive equipment, electromagnetic compatibility design.
The function of the program has been set circuit, testing whether the objectives meet the requirements of electromagnetic compatibility; at this time if does not meet the requirements, can be modified through the parameters to achieve the targets, such as the digital controller to adjust the working frequency, pulse rate of rise of round or re- selected components. Second, the protection design, including filtering, shielding, grounding and overlap design, or even space-time separation and frequency to avoid such improvements. Finally, adjustment of the layout design is done, including the overall layout of the inspection, the inspection shield gap, components and PCB layout of the inspection. Circuit and subsystem EMC design includes the following steps: component selection, circuit selection, filtering technology, grounding design, shielding design, circuit layout and system layout planning.
3ESD protection design.
In order to eliminate electrostatic discharge hazards, possible measures include: establishment of a sound shield, through the grounding of the metal shell to release the static charge to ground; internal circuit connection with the metal shell that grounding should be used; increase, such as silicon transient voltage absorbing diode (STVS) like fast protection components, the high voltage electric charge leakage into the ground; printed circuit board design to increase protection zone, will staff the charge plug board to vent through the shortest path into the ground.
A vehicle traveling data recorder hardware structure.
Figure 1 is a vehicle traveling data recorder hardware structure principle. Interference signal processing is achieved through optical isolation. Car equipment, power supply systems for the reliable operation of equipment, a great impact, good power supply circuit to filter out a lot of passing through the power line interference signal.
2 power supply part of the anti-jamming design.
The control module of the power supply circuit shown in Figure 2. Car batteries - the power from the generator enters the 24V_1, diode D16 is to prevent the power supply reverse polarity is wrong. Inductor L1, L2 of the power supply filtering, and common mode inductor L3, capacitor C8 with, you can filter out the peak pulse power supply. Is the impulse noise suppressor diode D24P6KE51A (TVS), it can quickly absorb the excess of the rated voltage spikes, transient through the current large, the maximum power of up to 500 ~ 1000W. E5 and the C9 capacitor further power supply filtering. Current through the filter and clean the chip LM2576 switching power supply of 5V systems transform power. E7 and capacitor C11 filter on the output 5V power supply, resistors R18 and LED D28 indicates the current if there is power.
In some of the higher power system reliability requirements, we can consider a wide input voltage range DC / DC power conversion module, shown in Figure 3. The DC / DC module input and output completely isolated, wide input range. 12V nominal input voltage of the DC / DC power supply allows the input range is 9 ~ 18V; nominal input voltage of 24V, DC / DC power module allows the input range is 18 ~ 36V.
Both circuits have gone through the practical application of the test proved that regardless of the car in gasoline or diesel vehicles are stable and reliable.
Circuit board design should pay attention to the interference problems:
Wiring board interference on the system performance of large, mainly from the wiring of the system to consider the following points.
● bold as power and ground, in power at the entrance to make use of large energy storage capacitors in the circuit board at the laying of free copper, which will greatly enhance the anti-jamming circuit board.
● In the chip to increase power and ground both ends of the decoupling capacitor, capacitance is 0.01 ~ 0.1μF, best to use ceramic capacitors to be added at each chip, which is very important.
● IO pin with a decoupling capacitor, to filter out a lot of external interference.
● minimize the wiring length of the high-frequency signal lines, in particular, the clock signal line, due to high frequency, wiring EMI issued the longer the more strongly. At the same time, we should try to reduce the length of the other signal lines.
● to make use of surface mount chips, so not only can reduce the circuit length, it will not happen due to vibration, shock and loosening of the situation.