Trends in power inductors

Meeting the demands for faster switching frequencies, lower inductance, and thinner profiles

BY THE ENGINEERING STAFF
Taiyo Yuden USA
Schaumburg, IL
http://www.yuden.us

Mobile phones, cameras, disk drives for notebook PCs, and portable audio players are just a few of the typical electronic devices now employing greater numbers of power inductors. Market pressures requiring smaller end devices with better performance pose tremendous design challenges—characterized by the need to integrate increasingly complex circuitry into the same or smaller circuit-board space. Greater end-device functionality translates into more circuit blocks requiring a correspondingly greater number of high-efficiency dc/dc converters with smaller, lower-profile inductors being in high demand.

Responding to this challenge, passive component manufacturers have focused their material science and fabrication efforts on developing and producing improved wirewound and multilayer chip-inductor designs that meet the market’s need for smaller case sizes with equivalent or better electrical performance than previously available components.

Smaller power inductors

The biggest challenge in designing power supplies for portable electronics—increasing efficiency while reducing size—is best met by using smaller inductors in the power supply design. One solution is to increase the switching frequency of the dc/dc converter, which results in lower inductance and smaller component size. In this scenario, the lower inductance value is offset by the higher frequency, accompanied by better transient response due to load fluctuation.

However, there are also tradeoffs. Increasing switching frequency also raises switching losses, which in turn lowers efficiency. Therefore, due to the interplay of other important circuit design characteristics that impact device performance, it is never simply a matter of only increasing switching frequency (see figure ).

Increasing switching frequency as a method of lowering inductance can have its tradeoffs.

In the recent past, switching frequencies hovered around 500 kHz with inductances of 4.7 to 10 µH. A number of factors, including better circuit designs, improved material science, and refined manufacturing techniques have boosted switching frequencies beyond 1 MHz.

However, further careful refinement of internal circuitry has recently yielded switching frequencies as high as 3 MHz, accompanied by inductance values below 2.0 µH. Based on projections, it will not be unusual to see switching frequencies of 6 to 8 MHz and inductance values well below 1 µH, resulting in further dramatic inductor miniaturization.

Higher switching frequency

The trend in 1-A-class inductors is toward lower-profile packaging, lower inductances, and faster switching frequencies. With a switching frequency of 300 kHz, for example, an inductor with a footprint of either 16 or 36 mm2 may be used.

Increasing switching frequency to 1.5 MHz allows a 9-mm2 -size inductor to be used, demonstrating that increasing switching frequency is accompanied by a corresponding reduction in package size. The clear implication for the future is that the key to providing smaller inductors lies in the ability of the component manufacturer to increase switching frequency while reducing inductance through continuous advancements in circuit design, materials and manufacturing.

In terms of package thickness, recent technical advances have reduced the profile of inductors used in cell phones, for example, from 2 mm a couple of years ago to 1 mm today. The technologies that made these significant improvements possible are paving the way to ever-thinner components to support the continuing device miniaturization trend that has captured the worldwide consumer electronics markets. Even so, simply adopting smaller inductors is not a complete solution.

Wirewound improvements

Smaller portable equipment requires more compact, high-efficiency dc/dc converters to stretch battery power maxed by added device functionality. Though it is difficult to reduce inductor size while maintaining the lower-resistance of larger components, some manufacturers are doing just that through better designs, material science refinements, and improved manufacturing techniques.

Though inductors are fairly simple structurally, there remains a host of technical hurdles to overcome in order to meet the market’s continuing miniaturization needs while providing desired performance. ■