The process of selecting a power inductor involves a series of trade-offs. Given the wide choice of inductors currently available, choosing the right one for a power converter is not always a simple task for designers of next-generation applications. Like many components in the industry, power inductors are being impacted by the development of smaller electronic devices that have enhanced functionality and require increased density of components on the board
By Baishakhi Dutta
Not all inductors are created equal. There is the inevitable trade-off between performance, size and cost that must be considered when selecting an inductor for a design. As a result, manufacturers bring out many series of similar inductors, allowing engineers to select a component well suited for their designs.
Know your application
Choice is all about options. In the case of inductors, knowing the options enables an engineer to choose a component that not only satisfies a circuit electronically, but also improves its overall performance.
The two most common applications for inductors are in the fields of RF and power electronics. Most inductor manufacturers recognise this, and have tailored their datasheets to provide engineers with the electrical parameters required to include their component into an RF or power circuit design.
Current rating
An inductor’s current rating is based on its ability to withstand DC current, and is essentially the thermal capability of the component. Usually specified in amperes DC (A DC) or milliamperes DC (mA DC), the DC current rating is the maximum current that should be allowed to flow through the component based on a specified ambient and maximum operating temperature.
If the specified current rating is exceeded and the ambient temperature is realistic, the component will exceed its maximum operating temperature, and may overheat and potentially fail. The notes on most specification sheets identify both the ambient temperature and temperature rise, or the ambient temperature and maximum operating temperature.
If the temperature rise is not specified, it can be calculated by simply subtracting the ambient temperature from the maximum operating temperature.
RF designs
For RF electronics, the main factors considered are the component’s quality (Q) factor and its self-resonant frequency (SRF). Additionally, an inductor’s tolerance should be considered. The Q factor is the ratio of an inductor’s reactance to its effective resistance. This value is frequency dependent, and therefore, the test frequency is often specified.
Specifically, Q affects the sharpness of a resonant filter and the centre frequency of an LC circuit. Because a high value of Q is preferred, datasheets specify a minimum Q value.
SRF simply describes the frequency at which an inductor quits working. For RF designs, an SRF should be chosen with a minimum value that exceeds the operating frequency of a circuit.
Power inductors
Power inductor parameters are generally focused on the device’s current parameters — incremental current and maximum current. Incremental current describes the current at which inductance is decreased normally by 5 per cent due to saturation. Saturation can be altered with different core materials and shapes.
The maximum current expresses the current at which the device will exceed the specified temperature rise. Under some situations, this may result in device failure.
Other factors to consider
One method of proper inductor component selection is to list the options for the core material and design, and outline the advantages and disadvantages of each. The options might include toroidal and/or gapped ferrite packages.
There is also a wide variety of moulded and/or open-construction inductors to choose from that are totally ungapped and, typically, are in either a straight or bobbin coil form. Each available core material can be combined with various wire sizes and turns to determine the actual inductance value of each inductor. However, the various core styles determine how well the part ultimately performs in different areas, such as shielding, saturation and DC resistance.
In this consumer-driven market, it is expected that portable electronics will continue to shrink to meet user expectations and demand. In order to maintain their competitive edge, today’s designers start with the most fundamental building blocks of design such as highly reliable and compact inductors.
Products available in the market
TDK Corporation
Product: Thin-film metal power inductors for automotive power supplies
TDK Corporation has expanded its portfolio of compact thin-film metal power inductors with a new type designed for demanding automotive applications. Measuring a mere 2.0mm x 1.6mm x 1.0mm, the new TDK TFM 201610 ALMA thin-film metal power inductor features what the company claims is the world’s highest rated current of 1.9A for a power inductor of its size. Its rated inductance is 2.2µH. Despite its miniature dimensions, the component provides a low DC resistance of 152mΩ. Based on a high-precision coil pattern, advanced plating technology and low-resistance materials, the thin-film metal power inductor helps improve the efficiency of power circuits. Moreover, the component has stable DC superposition characteristics, which serve to minimise the ripple current in the power circuit. Thanks to the use of a highly heat-resistant material, the TFM 201610 ALMA has a broad temperature range of -55°C to +125°C.
Contact details: www.tdk.eu
TDK Corporation
Product: Compact SMT high-current chokes
TDK Corporation has extended its portfolio of EPCOS ERU SMT power inductors with the ERU 19 choke series that comprises 10 different types. The inductance values of the new ERU chokes extend from 1.0µH to 30µH and their saturation currents range from 10.1A DC to 43A DC.
The outstanding feature of these new power inductors is their compact design. With a footprint of just 19.9mm x 20.5mm, they have low insertion heights of 8.35mm (1.0 µH) to 10.85mm (30 µH), depending on the type.
This low-profile design is based on a flat rectangular helical winding technology which results in lower losses. The DC resistances are between 1.20mΩ and 18.65mΩ.
Contact details: www.tdk.eu
Murata Manufacturing Co. Ltd
Product: Automotive grade 1212 case size wound power inductors with high current and low DC resistance
Murata has introduced the LQH3NPN_ME and LQH3NPZ_ME series of 1212 size (height: 1.5 mm) wound-type power inductors, featuring higher rated current and lower DC resistance levels as compared to the company’s previous inductors. The LQH3NPN_ME and LQH3NPZ_ME are designed to be incorporated into consumer products and automotive information devices.
The demand is growing for small inductors with high rated current levels for use in car navigation, car audio and other automotive information devices, just as it is increasing for use in consumer products, such as smartphones.
Contact details: www.murata.com
Vishay Intertechnology Inc.
Product: Low-profile, high-current power inductors save space and increase efficiency in portable electronics
Vishay Intertechnology Inc. has extended its IHHP series of low-profile, high-current power inductors with two new devices in the compact 3mm x 3mm 1212 case size. Offering a wide range of inductance values from 0.33µH to 10µH and low profiles of 0.8mm and 1.0mm, respectively, the Vishay Dale IHHP-1212ZH-01 and IHHP-1212AZ-01 are designed to save space and increase efficiency in portable electronics.
The IHHP-1212 ZH-01 and IHHP-1212AZ-01 feature maximum DCR down to 23 mΩ, high saturation current to 6.5A, and a heat rating current of up to 6.0A. The devices operate over a temperature range of -55 °C to +125 °C and are packaged in an RoHS-compliant, 100 per cent lead-free shielded construction.
Contact details: www.vishay.com
