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“In-vehicle 48V technology has some unique advantages: it can help reduce overall fuel consumption, reduce environmental hazards, and even improve engine performance. The core element of the technology is a powerful step-down (buck-boost) converter for which TDK Group supplies key passive components: power inductors and aluminum electrolytic capacitors.

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In-vehicle 48V technology has some unique advantages: it can help reduce overall fuel consumption, reduce environmental hazards, and even improve engine performance. The core element of the technology is a powerful step-down (buck-boost) converter for which TDK Group supplies key passive components: power inductors and aluminum electrolytic capacitors.

With the increasing number of complex powertrain management systems, comfort systems such as auxiliary Electronic heating, safety systems such as ABS (Anti-lock Braking System), ESP (electronic Stability System), and many other systems, the electrical load on the vehicle continues to increase. , and gradually become a large energy consumer. At the same time, it has driven a steady increase in the power level of the alternator. In the early 1880s, even luxury vehicles had their alternators outputting only about 0.7 kW. However, the power output required by the current vehicle has reached 3.5kW, which is almost seven times that of the original. The problem that comes with it is that if the 14V alternator is putting out that much power, it means that the generator output current will be as high as 250A. At this voltage/current ratio, the generator is only 70% efficient. This requires the input power of the engine to the generator to reach 5kW. Another disadvantage of high current is that it requires that the cross-sectional area of ​​the conductor must be large, which leads to a significant increase in vehicle weight and overall cost.

48V system can significantly improve efficiency

With the increasing demand for reducing fuel consumption and CO2 emissions, the market needs to find targeted solutions. 48V technology came into being and brought many advantages because it enabled many energy saving measures that could not be solved by 12V systems alone. Its functional features include:

When the power is greater than 5kW, the energy recovery efficiency is very high

Expanded start-stop functions such as slow start or smooth stop

Electrified units such as turbochargers and electric power steering

Supports micro- and mild-hybrid solutions

The 48V system is not a complete replacement for the existing 12V architecture. Instead, this approach allows us to expand the 12V system to handle higher power loads, while also coupling the 48V system to these systems through a buck converter setup. Figure 1 explains the principle of this architecture. Regular lead-acid or lead-acid gel batteries are used for the 12V rating, while lithium-ion batteries are used for the 48V rating. Double layer capacitors can also be connected in parallel here to improve electrical energy storage during recovery.

Figure 1: Architecture of the integrated 12/48V on-board power supply

The main improvement lies in setting the generator’s level to a 48V rating for a higher power output and energy efficiency rating. The two voltage levels are connected through a bidirectional buck converter unit.

High-efficiency coupling through buck-boost converters

In an integrated 12/48V system, the most important component is the buck-boost converter, which allows energy to flow bidirectionally between two different voltage levels and provides a power output of 2 to 5kW. Figure 2 shows the circuit schematic of this converter. In normal mode, the converter acts as a buck converter, outputting the power generated by the 48V system into the 12V system. In this working mode, T2 is always in the blocking state, while T1 works as a switch. If you need to output 48V level voltage, you must use boost mode. In this case, T1 is always on, while T2 works in pulse mode. In order to minimize the ripple current and voltage, 6 or 8 modules need to be connected in parallel in practice.

Figure 2: Buck Converter Circuit Diagram

In addition to switching transistors, EPCOS power inductors and storage capacitors are the core components of buck-boost converters.

The TDK Group has developed two new series of EPCOS power inductors as converter energy storage and smoothing chokes. For example, the surface mount (SMD) type ERU 27 series inductors have high current capability and are packaged in a compact size of only 30mm x 27.8mm (left side of Figure 3). Its insertion height is 15.5mm or 20.3mm, depending on the inductance value. This compact design is achieved using flat windings with a high fill factor. The inductors are available in six different sizes, with inductance ranging from 3.5µH to 15µH, with saturation current ranging between 19 A and 49 A. To improve the mechanical stability of the components on the PCB, in addition to the two winding pads, a third pad has been added to this product.

In addition to this SMD product, EPCOS ERU 33 series products with PTH terminals (right side in Figure 3) are available for selection with rated inductance values ​​ranging from 3.2µH to 10µH, depending on the model. To ensure a saturation current of 79A, the resistance of the Inductor is only 0.85 mΩ. The power chokes of this series are 33mm×33mm×15mm in size, suitable for an operating temperature range of -40°C to +150°C, RoHS compliant, and pass the AEC-Q200 reliability test. In addition to the standard ERU 27 and ERU 33 models, we can also customize according to the specific needs of our customers.

Figure 3: Compact EPCOS power inductors with current capacity up to 75 A

Extreme Vibration Resistant Capacitor with High Ripple Current Output Capability

In addition to the inductor, the core elements of the buck converter include rugged aluminum electrolytic capacitors for energy storage and smoothing. The EPCOS B41689 and B41789 series (Fig. 4) are specially designed to meet the stringent requirements of automotive electronics, with exceptional vibration resistance of up to 60 times the acceleration of gravity. In addition, star-soldered and capacitor versions with cathode plate contacts at both ends optimize capacitor installation, keeping the capacitor’s equivalent series inductance (ESL) low.

Figure 4: EPCOS aluminum electrolytic capacitors for automotive electronics have a high vibration resistance of up to 60g and a maximum operating temperature of 150°C.

Due to the built-in multiple contacts, the equivalent series resistance (ESR) of these capacitors is also quite low, resulting in higher ripple current capability and lower losses. These capacitors have a continuous ripple current capability of 29.5 A at 125 °C ambient temperature, depending on the capacitor type. Among them, the automotive series are designed for applications with rated voltages of 25V, 40V (or 12V) and 63V (or 48V). At these voltage levels, they can work in new vehicle power systems with two different voltage levels. Capacities in this capacitor are available from 360µF to 4500µF.

In addition to core components such as power inductors and aluminum electrolytic capacitors, buck converters also include a range of other TDK Group components such as multilayer ceramic capacitors (MLCCs), current transformers and varistors.