Power Electronics

Shrinking Inductors Help Build Smaller Power Converters

A major reason for the migration to higher switching frequencies has been the need to reduce the size of the inductor required to complete a dc-dc converter design. As described in a recent Analog Feedback column, switching regulators operating in the vicinity of 3 MHz to 4 MHz are becoming common and some are even pushing into the 5-MHz to 10-MHz range (see “Multi-Megahertz Switching Gains Momentum,” Power Electronics Technology, April 2006, pages 46-48). Complementing this trend is the improvement in inductor technology, which is yielding smaller components with higher current ratings.

Some of the recently introduced inductors highlight the progress that magnetics suppliers have made in shrinking their components for space-constrained board-mounted power supplies. One example comes from Vishay Intertechnology (www.vishay.com), which has extended its IHLP family of low-profile, high-current inductors by adding devices in the 2525-size footprint with a 3-mm package height. Targeting voltage regulator modules (VRMs) and dc-to-dc converters, the Vishay Dale IHLP-2525CZ-11 inductors feature inductance values ranging from 22 µH down to 1 µH.

Although these parts occupy the standard 2525 footprint (0.255 in. × 0.270 in.) shared by lower-profile IHLP devices, their increased height enables them to offer higher current ratings and lower DCR values. According to the vendor, these devices provide the lowest ratio of DCR to µH in their package size.

These inductors specify saturation currents ranging from 2.5 A to 9.5 A, typical DCR values ranging from 7.6 mΩ to 128.9 mΩ, and maximum DCR values ranging from 8 mΩ to 135 mΩ. Standard inductance tolerance is ±20%.

The IHLP-2525CZ-11 inductors handle high transient current spikes without hard saturation and operate at a frequency up to 1 MHz. Packaged in an RoHS-compliant, 100% lead-free shielded-composite construction that reduces buzz noise, the devices operate across the -55°C to 125°C temperature range with high resistance to thermal shock, moisture, mechanical shock and vibration.

Samples and production quantities are available now. Pricing for U.S. delivery only is $0.32 per unit in 10,000-piece quantities.

Another recent introduction is the Coiltronics SD3110 Series of shielded-drum ferrite-core inductors from Cooper Bussmann Electronic Technologies, a business unit of Cooper Bussmann (www.cooperbussmann.com). Featuring a footprint of only 3.1 mm × 3.1 mm and a package height of 1 mm, these inductors claim “one of the highest power density-to-size ratios of any surface-mount inductor on the market.” Inductance values range from 0.5 µH at 2.27 A to 220 µH at 0.106 A.

The ferrite shield reduces EMI effects when compared to unshielded-drum core structures. The design is also easier for pick and place machines to recognize and properly orient the parts, which are more easily detected by vision systems. The configuration is also a stronger mechanical package.

Another series of low-profile inductors comes from Taiyo Yuden U.S.A. (www.yuden.us). Its NR6012 series of 6-mm × 6-mm × 1.2-mm power inductors target dc-dc converter choke coil applications in the LCD panels of notebook PCs (see the figure). The 11 models in the NR6012 series offer a broad selection of low dc resistance (0.092 Ω to 2.18 Ω) and high inductance ratings (3 µH to 100 µH). These parts also offer high current ratings (320 mA to 1730 mA) for the 6-mm × 6-mm form factor. The company expects to add part numbers with even higher current ratings in the near future.

In notebook PC applications, LCD power circuits require dc-dc converters with high current handling capability and a stable dc-voltage supply. Posing a design challenge, the demand for lower-profile mobile equipment is driving a corresponding need for choke coils with higher current capacity and a lower physical profile. However, boosting current capability necessitates increasing the size of the core and thickening the lead wire inside the inductor, both of which make reducing the size and profile of the device very difficult.

In response to this challenge, Taiyo Yuden departed from the conventional round-drum/sleeve-core technology and developed a sleeveless square-core winding that eliminates wasted space and thickens the lead wire inside the inductor to achieve the lowest possible dc resistance. Moreover, the NR6012 series' special ferrite-based resin covering further reduces size and enables a current rating of 1 A at 10 µH. Available now in production quantities, the units are priced at $0.30 each in sample quantities.

Another vendor, Coilcraft (www.coilcraft.com), is about to introduce a family of low-profile, shielded power inductors. These components feature package heights under 2 mm, a very small (3 mm2 or 4 mm2) footprint and inductance values up to 3300 µH. According to the vendor, these inductance values exceed anything currently on the market in parts this small. Saturation current ratings are also said to be exceptionally high, allowing the designer to use a smaller, lower-profile inductor in the application.

The low-inductance parts should find use in dc-dc converters, while the high-inductance parts will be particularly well suited to power supplies for EL and LED backlights. Pricing ranges from $0.27 to $0.29 per unit in quantities of 10,000.

Naturally, size reduction is not the only area of inductor development. Vendors are also lowering the amount of radiation produced by their components. Next month, Gowanda Electronics (www.gowanda.com) will unveil its MG series inductors, which are manufactured using a proprietary approach that assures the inductors have nonmagnetic characteristics.

The MG series specifically targets applications that are magnetically sensitive, particularly test equipment and devices as well as medical diagnostic equipment such as imaging equipment. In their role as filters, the nonmagnetic MG inductors block certain frequencies that otherwise would compromise the performance of the equipment or device. With their 0.01-µH to 4.7-µH inductance range and 260-mA to 3835-mA current ratings, the MG series inductors may also find use in dc-dc converters.

An RoHS-compliant version of the MG series is also available. Available in through-hole and surface-mount versions, the inductors are priced starting at $0.79 each in production quantities.

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