Axial-lead Hybrid Polymer AI Caps with Highest Current Ratings

TDK has succeeded in developing the world’s first hybrid polymer aluminium electrolytic capacitor in axial design, resulting in automotive capacitors with highest current ratings. The new technology offers an unrivalled capacitance of 1300 µF at a rated voltage of 25 V and an extremely low ESR of just 3 mΩ. The new capacitor’s dimensions are a compact 14 mm x 25 mm. With the Epcos axial-lead hybrid polymer aluminium electrolytic capacitors, too, the company is setting a new benchmark.

 

Features

The new hybrid polymer aluminium electrolytic capacitors feature an Equivalent Series Resistance (ESR) that is up to 8.5 times smaller than that of standard aluminium electrolytic capacitors. As a result, the new capacitors offer an extremely high ripple current capability of up to 16 A at 10 kHz and 125 °C case temperature, compared to about 6 A for standard types. 

Thanks to their high capacitance per volume, where they are indispensable in most automotive systems, aluminium electrolytic capacitors stabilize the operating voltage and thereby safeguard the reliable functioning of the systems. In recent years, TDK has developed and continuously optimized aluminium electrolytic capacitors especially for automotive applications. The culmination of these development efforts so far have been axial-lead types with a high vibration strength of up to 60 g and for permissible operating temperatures of up to 150 °C. One of the key characteristics of aluminium electrolytic capacitors is their ESR: When an alternating current – the ripple current – is applied, power losses occur proportionately to the ESR that heats up the component (PL = ESR x I2AC). ESR, in combination with the thermal resistance, is thus the main factor limiting the current capability of an aluminium electrolytic capacitor. 

 

Reduction of Equivalent Series Resistance

Hybrid polymer technology significantly reduces the ESR. Therefore, in order to lower the ESR substantially, the new caps have turned to hybrid polymer technology, which combines a polymer with a high conductivity of around 1000 S/cm with a liquid electrolyte. 

In addition to lowering the ESR, hybrid technology offers one other advantage over the use of polymers alone: Hybrid polymer aluminium electrolytic capacitors are self-healing and are able to re-oxidize defects in the dielectric oxide layer of the al cap. As a result hybrid polymer al caps feature higher dielectric strength, temperature resistance and durability than pure polymer aluminium capacitors. 

Conventional hybrid polymer technology offers a ripple current capability that is 2 to 5 times higher, depending on temperature and rated voltage. The capacitance values and rated voltages of the capacitors currently available on the market, however, are relatively low. Typical values are 270 µF at a rated voltage of 35 V with dimensions of 10 mm x 10 mm (D x H) in the SMD version. Such capacitors have ESR values in the range from 10 mΩ to 15 mΩ. 

The patented material, process and design innovations include: 

• Optimized structure and composition of the solid/fluid electrolyte system 
• Filling of polymer material into large windings 
•  Extremely low metal resistance by means of multi-tab connectors in order to exploit the high conductivity of the polymer in combination with very low ESL, even in large designs.

 

Advanced Ferrite Materials and Geometries 

New ferrite material and improved geometries for the core designs (distributed air-gap) ensure improved efficiency, which – apart from miniaturization – is the most important development goal in the design of power supply units. Every tenth of a percent counts. Except for the power semiconductors, ferrite cores are the decisive factor for efficiency. 

In order to be able to exploit the advantages of new (wide bandgap) semiconductors, TDK has developed the new PC200 ferrite material based on MnZn that is designed for the frequency range between 0.7 MHz and 4 MHz. The maximum transmissible power is reached at a switching frequency of between 1.8 MHz and 2 MHz and an operating temperature of 100 °C. The Curie temperature is in excess of 250 °C and the PC200 ferrite material is particularly suitable for transformers based on ring or planar core topologies. With its optimum performance at a frequency of about 2 MHz the new PC200 MnZn ferrite material is ideally suited for topologies of power supplies that are based on new wide bandgap semiconductors such as GaN and SiC. 

 

Wide-Bandgap Semiconductors

New wide bandgap semiconductors such as GaN and SiC are facilitating further advances, because they can switch higher frequencies with higher slew rates and lower losses. This means that, in principle, it is possible to use considerably smaller inductors and transformers, or to handle higher power ratings with a component of the same size. The disadvantage is that conventional existing power ferrite materials are not designed for frequencies in the MHz range, where they exhibit greater losses than at lower frequencies. 

 

Single Air Gaps

The use of single air gaps in ferrite cores is a common technique today for delaying the core saturation and thus increase the performance. These relatively large, single gaps however result in a higher fringing flux effect, leading to additional copper losses, particularly at high frequencies. With new geometries and the core manufacturing technique of distributed air gaps, TDK is the first ferrite core manufacturer to offer an elegant solution for reducing electromagnetic emissions and thus heating. By arranging the gaps in the center post, the magnetic field emissions to the environment is effectively prevented. 

Different sized cores are available with three distributed air gaps in E, EQ, ER, ETD, PM and PQ core design. Solutions with three air gaps offer the best cost/performance ratio for applications in which the switching frequency is 2 or 3 times higher than the original frequency. This enables the losses to be reduced by up to 70 percent.

 

About TDK Corporation

TDK Corporation is a leading electronics company based in Tokyo, Japan. It was established in 1935 to commercialize ferrite, a key material in electronic and magnetic products. TDK';s comprehensive portfolio features passive components such as ceramic, aluminium electrolytic and film capacitors, as well as magnetics, high-frequency, and piezo and protection devices. The product spectrum also includes sensors and sensor systems such as temperature and pressure, magnetic, and MEMS sensors. In addition, TDK provides power supplies and energy devices, magnetic heads and more. These products are marketed under the product brands TDK, EPCOS, InvenSense, Micronas, Tronics and TDK-Lambda. TDK focuses on demanding markets in the areas of information and communication technology and automotive, industrial and consumer electronics. The company has a network of design and manufacturing locations and sales offices in Asia, Europe, and in North and South America. In fiscal 2019, TDK posted total sales of USD 12.5 billion and employed about 105,000 people worldwide.

 

This article originally appeared in the Bodo’s Power Systems magazine.