Sleeveless inductors answer industrial automation electronics design challenges

Design engineers building electronic controllers and power supplies for industrial machinery — such as robots and automated assembly equipment — face tough design challenges. The end-product typically operates in an environment where heat and vibration are commonplace, space is tight and cost-restraints even tighter. Yet, industrial equipment must operate continuously and efficiently for months at a stretch across many years.

Figure 1: Compared with conventional sleeved inductors, TAIYO YUDEN’s sleeveless design shrinks component size, improves function and allows the use of larger terminal electrodes for better thermal and mechanical performance. Source: TAIYO YUDEN

The humble inductor is a key component in industrial machinery’s electronic circuits. Dozens of the devices could be used in an industrial machine — for example, acting as an energy storage device in a switch mode power supply — and failure of any one of them could mean a lengthy and expensive factory shut-down.

That makes selecting an inductor a tricky business. Designers face trade-offs between cost, size, performance and reliability. But now, an innovative sleeveless inductor design from TAIYO YUDEN not only eliminates several of those compromises but also introduces some key advantages over conventional sleeved inductor products.

Drawbacks of sleeved inductors

Conventional inductors shield the coil/core with an outer sleeve. The arrangement works satisfactorily but there are some drawbacks. For example, the sleeved design results in an air gap between the inductor’s copper coil and the sleeve. This air gap decreases the inductor’s peak or “saturation” current (ISAT) capacity. This is an important performance characteristic quantifying the inductor’s ability to maintain inductance at high current levels. Higher ISAT values generally lead to lower losses and greater efficiency. Moreover, the air gap reduces the sleeved inductor’s quality (or “Q”) factor. While Q factor varies with operating frequency, generally, a higher Q factor lowers the inductor’s losses.

From a mechanical perspective, the sleeved design not only increases the inductor’s overall dimensions and weight, but it also limits the size of the component’s terminal electrodes. The continuous current (IRMS) passing through an inductor causes the component to heat up. Smaller electrodes reduce the amount of heat the component can sink through its terminal pads to the PCB, putting a limit on its continuous current-carrying capacity before overheating occurs.

TAIYO YUDEN’s new NR series M-type family of sleeveless inductors eliminates the sleeve used to shield conventional components and instead covers the core with a special metal resin. From an electrical perspective, the use of the resin eliminates the air gap between the sleeve and coil/core, improving the inductor’s ISAT and Q factor.

Mechanically, the sleeveless design reduces the size and weight of the solution compared with an identical inductance value sleeved device, enabling more compact end-products. Moreover, the sleeveless design allows for larger terminal electrodes that sink more heat to the PCB, reducing the self-heating effect and allowing for greater continuous current capacity. The larger terminal electrodes also endow the component with greater resistance to joint failure following repeated -40° C to 125˚ C heat or vibration cycling.

Building on proven technology

The NR series M-type inductors are based on proven technology — TAIYO YUDEN introduced sleeveless inductors to the market with its NR series S-type family of products back in 2012. Those products were targeted at the automotive sector for applications such as infotainment, telematics and air conditioning. Tens of billions of NR series S-type inductors have since performed flawlessly.

However, the NR series M-type family features two significant technical enhancements over the NR series S-type products, making them even more suited to industrial machinery. First, where the NR series S-type family employed a ferrite core and ferrite resin, advancements in resin technology have allowed TAIYO YUDEN to upgrade the NR series M-type products to a hybrid solution of ferrite core and high-density magnetic metal resin. The metal resin further improves the device’s ISAT. Second, The NR series S-type product features an enhanced terminal electrode design that not only improves coplanarity during the PCB surface-mount assembly process (eliminating false mounting-error detection), but also creates larger side solder-fillets (enhancing joint visibility during automatic optical inspection (AOI)).

The TAIYO YUDEN NR series M-type family of inductors offers a good balance between performance and cost. The components are available with inductance values ranging from 1 to 470 µH for the 6.0 x 6.0 x 4.5 mm size, 0.47 to 470 µH for the 5.0 x 5.0 x 3.0 mm size and 0.47 to 100 µH for the 3.0 x 3.0 x 1.5 mm size. The products are available now for the North American market. Visit the TAIYO YUDEN website for more information.