Re-Engineering the Power Inductor for Automotive “Electric Everything"

April 23, 2020 KEMET ELECTRONICS CORPORATION

The trend in automotive towards electrification of every aspect of today’s vehicles places extreme demands on DC/DC converters to provide stable power over a wide temperature range, and to deliver high reliability and energy efficiency, within tight space constraints - such as the electronic control unit (ECU). A new generation of power inductors delivers superior characteristics to meet these demands.

Electric Everything

In the past, car salespeople have used the phrase “electric everything” to describe extravagant luxuries such as powered windows and a sunroof, and maybe - at the extreme high end - adjustable door mirrors and heated seats. In today’s world, it’s almost a literal statement. Major functions including power steering, engine ancillaries such as the water pump, and automatic clutch and gearbox controls are converting to electric operation. And although electronic fuel injection is a long-established feature to boost performance and fuel efficiency and cut emissions, hybrid and battery-electric vehicles (HEV/BEV) are taking electrification to the limit by replacing the entire drivetrain and energy store with electrical equivalents.

Electrification brings advantages such as cost reduction, lightness, and the opportunity for flexible electronic control that allows performance to be adapted and new features to be added and subsequently improved through periodic software updates.

Improving safety is another goal that deserves special attention. Advanced Driver Assistance Systems (ADAS) such as autonomous steering and braking, advanced lighting systems inside and out, and connected-car functionality such as V2X and emergency support services introduce many more electronic modules such as LED drivers and sensors including cameras, radar, lidar, and wireless modules connected to control units that comprise a mix of conventional computing and AI inferencing.

From the era when the most advanced vehicles would feature a single electronic control unit (ECU) to handle engine management, we are now in an age where even an average car may contain over 100 ECUs, or domain controllers, to manage numerous the body electronics, powertrain, comfort, safety, and infotainment systems on board.

The Importance of Stable Power

Intense electrification presents severe challenges for designers of automotive electronic equipment. ECUs must perform consistently over a wide temperature range, particularly in under-the-hood locations or areas exposed to sunlight. They must also have high resistance to shock and vibration, coexist and not interfere with other systems in the vehicle, and comply with extreme space constraints behind the dashboard, inside door cavities, in the engine bay, behind headlamps, and inside mechatronic assemblies such as motorized systems.

Changing approaches to ECU power supply design can help achieve these goals. Output stability is needed over a wide temperature range. Although conventional inductors that typically feature a conductive coil wound around a ferrite core display stable inductance over a wide current range, inductance falls sharply at values above the saturation current. Moreover, the saturation current is temperature dependent, reducing at higher temperatures. In addition to offering improved saturation characteristics and stability over a wide temperature range, inductors for automotive applications should also offer low DC resistance to avoid unwanted self-heating and minimize energy losses thereby contributing to increasing overall vehicle efficiency.

New Metal-Composite Inductors

A new class of metal-composite inductors is emerging to meet these demands. Devices such as KEMET’s MPXV inductors comprise a copper coil that is terminated to a large solderable pad and encased within a moulded external core (figure 1).

Figure 1. Construction of metal-composite inductor.

The core is made from insulated iron particles, the predominant use of iron results in a more stable temperature coefficient than typical ferrite formulas. To create the core, the powdered iron is mixed with a binder and pressed into the desired core shape around the coil. The physical properties create an inherent distributed air gap that allows the core to store higher levels of magnetic flux than ferrites.

KEMET’s MPXV power inductors combine low DC resistance with a slow saturation characteristic that is also more stable over temperature than that of traditional ferrite-core inductors (figure 2). The superior saturation characteristic enables DC/DC switching power supplies to maintain function in situations where inrush current is high, while the improved temperature stability enables engineers to design with reliable thermal consideration. MPXV power inductors also benefit from EMI shielding, which reduces flux leakage and interference, and are automotive qualified to AEC-Q200.

Figure 2. Comparison of metal-composite and ferrite-core inductor saturation.

With parameters specified up to 155°C and further desirable performance attributes such as low acoustic noise and high resistance to shock and vibration up to 30G, the inductors can be used in all areas of the vehicle including the challenging operating environments found under the hood. They can thus help to drive the ongoing process of electrification, aiding the delivery of stable and efficient power to subsystems such as LED headlights, meter cluster panels, head-up displays (HUD), electric water pumps (EWP), electric oil pumps (EOP), and electric power steering (EPS).

MPXV series inductors are available in a wide range of inductance values from 0.10µH to 100.00µH, in surface-mount packages that exploit the easy formability of the moulded core to offer a low profile to fulfill applications that are subject to tight space constraints.

Conclusion

New internal-coil construction and innovative metal-composite materials technology have enabled the emergence of a new class of inductors that deliver favorable saturation characteristics and temperature stability to address the latest automotive applications as electrification spreads to every aspect of the vehicle. New inductors such as KEMET’s MPXV series are taking the industry forward into the age of true “electric everything”.

For more information on the MPXV series, or any of KEMET’s METCOM products, please visit: www.KEMET.com/metcom

About the Author

Michael Freitag is the Director of Product Management for Magnetic, Sensor and Actuators EMEA at KEMET Electronics Corporation. He has over 19 years’ experience working in the electronics industry, with over 15 years at KEMET where he started as a sales representative in Germany in 2004. He graduated from University of Applied Science, Dortmund with a Diploma in Electrical, Electronic and Communications Engineering Technology.

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