DC-DC converters are mostly used as power supply for on-board electronic equipment including ECU (electronic control unit).

DC-DC converter has the characteristics of high efficiency, but because it is a switching power supply, it will produce radiated noise due to semiconductor switches, resulting in adverse effects on other electronic systems, or interference on vehicle antenna, resulting in obstacles to the signal reception of AM / FM broadcasting and terrestrial digital TV. At the same time, if multiple ECUs are centrally configured in the engine compartment or instrument panel, they are easy to be affected by radiated noise.

Eliminating the source of noise is the basic of EMC countermeasures. To achieve smooth vehicle connection convenience and automatic driving system, the power line of vehicle electronic equipment requires a wide range of radiation noise countermeasures.

TDK’s on-board 3-terminal through filter yff-ac / AH series is an EMC countermeasure component with high reliability and high current for on-board electronic equipment by optimizing materials and design. Although the volume is small, it has good attenuation characteristics in a wide frequency band. Therefore, as an on-board electronic equipment, it has a significant effect on the radiated noise of the power line.

//DC-DC converter of ECU is the main source of radiated noise

There are more than 100 ECUs in high-end vehicles. It is connected through a harness that ties the power line supplied by the battery and the signal line used to exchange information between the ECU. Figure 1 shows the main noise sources and transmission routes of the on-board network.

What are the radiation noise countermeasures for the power line of on-board electronic equipment

Figure 1: main noise sources in vehicle network power line

//Solution: Countermeasures for radiated noise of power line of on-board electronic equipment

According to the evaluation and measurement examples, the radiated noise countermeasures of the power line of on-board electronic equipment using TDK 3 terminal through filter yff-ac / AH series are introduced below.

Figure 2 shows an evaluation circuit for investigating the radiated noise generated by the power supply circuit of on-board electronic equipment and a schematic diagram of the 3M anechoic chamber method measurement system. Connect the DC power supply (12V) equivalent to the on-board battery with the evaluation circuit (DUT: equipment under test) through the cable, and measure the noise level (electric field strength) through the antenna separated by 3M.

What are the radiation noise countermeasures for the power line of on-board electronic equipment

Figure 2: power line radiated noise evaluation circuit and 3M method anechoic chamber measurement system

The purpose of EMI test is to protect on-board receiving equipment such as radio and television from radiated noise. Its international EMC standard is specified by CISPR25, and its limit value is much more stringent than that of civil equipment.

In the above evaluation circuit, the frequency electric field intensity (radiated noise level) when there is no filter, 4-device LPF (low-pass filter) is inserted, and 3-terminal through filter is inserted are compared (Fig. 3). The red line box indicates the radiated noise level limit of FM band and terrestrial digital TV specified by the extremely strict CISPR25 class 5.

What are the radiation noise countermeasures for the power line of on-board electronic equipment

Figure 3: radiated noise suppression effect and advantages of 3-terminal through filter

When there is no filter, the noise level in the terrestrial digital TV band is significantly higher than the limit value, but after inserting LPF and 3-terminal through filter, the noise level is suppressed below the limit value. However, LPF is a 4-device filter composed of 2 MLCC, sheet magnetic beads and metal coils. The 3-terminal through filter only needs one device to realize the limit value required by CISPR25 class 5. In terms of reducing component cost, mounting cost and saving mounting space, 3-terminal through filter also has great advantages.

Responsible editor: GT

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