Power inductor for vehicle information equipment

Foreword

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In recent years, with the continuous advancement of the electronic process of automobiles, various digital devices for vehicles, including audio and navigation systems, have been increasing. In addition, countries have stipulated the obligation to mount rear view cameras, lane departure warning systems, and automatic emergency braking systems, so that the demand for power inductors used in circuits for converting power supply voltages in these digital devices has increased significantly.

There are many types of power inductors. One of the most representative models is a copper wire wrapped with an insulating coating on the outside of the drum core, with a sleeve core around it, and the coating is a resin made of a mixed magnetic material. The other is a metal composite type in which an air core coil and a metal powder material are integrally formed. The terminal electrode is also classified into a plurality of types such as a metal frame terminal, a solder electrode, and a conductive adhesive.

On the other hand, electronic components for digital devices for vehicles are pursuing the requirements of miniaturization, high temperature resistance, and high reliability. Here we will introduce a wound inductor (up to the LQH**PB series of Figure 1) that can operate at temperatures up to 105 °C.

Figure 1: Power Inductor LQH**PB Series for Automotive Information Equipment (from left to right: 32PB, 43PB, 5BPB)

The above LQH series is used around the insulating coated copper wire wound around the drum core, and the magnetic resin used serves to reduce the leakage flux, protect the insulated coated copper wire, and improve the strength of the product. An overview of the structure is shown in Figure 2.

Figure 2: Introduction to the construction of the LQH series

Product characteristics

Improvement of thermal shock resistance (improvement of magnetic resin material)

Automotive electronic components are required to perform a thermal shock test with a minimum service temperature of 1000 cycles. Among them, the in-vehicle information device is subjected to a thermal shock test of 1000 cycles at a temperature of -40 ° C ⇔ + 105 ° C.

The coating material "magnetic resin" of the wound inductor contains epoxy resin, which realizes a large expansion and contraction of the glass transition point as a limit, and a thermal shock test at -40 ° C ⇔ + 105 ° C / 1000 rounds In the case, the magnetic resin also cracks. Further, a ferrite material is used for the drum core portion of the inductor, and the ferrite material and the magnetic resin have a difference in thermal expansion coefficient. If the difference in thermal expansion coefficient is large, the expansion and contraction of the magnetic resin causes stress to be transmitted to the drum core, causing cracks in the drum core.

This time, we have developed a resin for in-vehicle information equipment by adding a material that enhances the strength of the hardened coating film. This resin suppresses cracking of the magnetic resin and reduces the difference in thermal expansion coefficient between the drum core and the magnetic resin. The small drum core stress can also suppress the crack of the drum core. Through these improvements in thermal shock resistance, we have developed new products that do not cause magnetic resin and drum core cracking even in the thermal shock test of -40 ° C ⇔ + 105 ° C / 1000 wheels required for in-vehicle information equipment. .

The relationship between the number of thermal shock input cycles and the crack occurrence rate is shown in Fig. 3. In general, the magnetic resin in the civilian market will crack under 1000 rounds, and the magnetic resin used in the in-vehicle information equipment developed by us has not produced cracks after 2000 rounds. It also ensures that cracks do not occur even in the toughest thermal shock test at -40 ° C ⇔ + 125 ° C.

Figure 3: Thermal shock test input cycle vs. crack rate

The appearance pictures and main electrical characteristics before and after the -40 ° C ⇔ + 105 ° C / 2000 round thermal shock test are shown in Figures 4 and 5.

No cracks were observed in both the magnetic resin and the drum core. In addition, changes in electrical characteristics are also controlled within ±1%. The appearance of -40 ° C ⇔ + 105 ° C without any damage, and the electrical characteristics remain stable, which makes it a product that can meet the performance requirements of automotive electronic components.

Figure 4: Appearance changes before and after thermal shock experiments

Figure 5: Changes in main electrical characteristics before and after thermal shock experiments

Product list

The following four series of power inductors for automotive information equipment have been commercialized. The product outlines are shown in Table 1.

The size list has been commercialized from a maximum of 3.2 × 2.5 × 1.7mm to a maximum of 5.0 × 5.0 × 2.2mm.

Table 1. Product summary of power inductor LQH**PB series for in-vehicle information equipment

Figure 6: DC Overlap Characteristics of Representative Items (1.0μH/4.7μH/22μH)

Conclusion

We have developed the high reliability power inductor LQH**PB series for in-vehicle information equipment. Because it can provide such products, it is a multi-functional vehicle and improves safety. In particular, the use of EV/PHEV to reduce environmental impact has contributed to the protection of the global environment.

In addition, in the future, we will actively respond to the demand for miniaturization and high-temperature environments that are gradually expanding today, and improve the function of the wound inductors to contribute to the needs of the automotive market.