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High Performance Inductor Designs Meet Advanced Electronics Needs

The power demands of electronic devices have increased substantially over the last couple of years. Today’s designs operate at higher switching frequencies, require ever-more component performance support and are continually shrinking in size. An integral component in virtually every circuit that regulates power are inductors. They are a fundamental element in the voltage regulator topology for a wide range of applications in automobiles, industrial and consumer electronics. Inductors are also very important in DC/DC converter designs. Important for efficient DC/DC converter designs, high-powered inductors provide the necessary very low DC resistance (DCR) characteristics needed for power conversion and supply circuit requirements.

Up until now, conventional inductor technology has been falling behind in meeting the high- performance demands of these advanced electronic devices. Understanding the present and underserved requirements for power inductors, Bourns has developed several model series that feature rated DC current up to 70 A to meet the challenges of the market.

Key Inductor Specifications

The major specifications to evaluate in Bourns® inductor products are the Irms and Isat. The Irms specification is the DC current that causes the inductor temperature to rise, for instance by 40 °C and Isat is the DC current that causes the inductance to decrease, for instance by 10–30 percent. Why these specifications are important is because the current in a switching converter is rarely stable, and the variation will be the result of transients, spikes, or sudden load and supply changes. The fall off of inductance with increasing current is a primary characteristic that must be considered in any design. The temperature rise of the inductor during operation should be carefully evaluated. Ripple current passing through the inductor in a switching converter will drive up core loss resulting in additional power dissipation on top of copper wire loss.

Other inductor selection criteria include where it will be placed on the circuit board, keeping in mind the sensitivity of components that will be in its immediate vicinity. Applications require either a shielded or non-shielded inductor where each category has its advantages and disadvantages. The main advantage of a shielded inductor is its low radiation, which can be characterized. In comparison, the magnetic flux of a non-shielded inductor is neither steady nor confined to a given vicinity. The downside of shielded inductors is their larger size, a faster inductance roll-down, greater cost, and a lower current rating. The advantages of non-shielded components are that they are smaller, rated for higher current, and many times, cost less. However, these advantages may not be important factors if the radiation environment is a key requirement in a design.

Bourns® Inductive Components

Bourns® inductive components include chip inductors, power inductors, AEC-Q200 compliant inductors, power chokes, and common mode chokes. This extensive inductor product portfolio is offered with through-hole and surface mount (SMD) packages in a large variety of sizes and inductance for a wide range of power applications.

The Bourns line of surface mount packaged magnetics include signal transformers, signal line common mode chokes, multilayer/wire wound chip inductors, and non-shielded, semi-shielded, shielded high current power inductor series. The power chokes category, which consists of non-shielded, semi-shielded, shielded, and high current power inductor series leverages Bourns’ extensive magnetics product design expertise.

Inductors for Energy Storage

Inductors are used as the energy storage device for all switching converters. Energy is being stored in an inductor in the form of magnetic flux at the switch-on cycle. Flux then collapses and is transformed back to electrical energy for maintaining supply to the load during the switch-off cycle. To ascertain energy storage requirements, the energy stored is calculated as E = ½ LI2 (Joules) where I is the inductor current (A) and L is the inductance (H).

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Figure 1: The current through the inductor is transformed to produce magnetic fields. The inductor is charged when the circuit is on.

Figure 2: When the circuit is off, the inductor acts as a current source, discharging the current that flows through the circuit as the magnetic fluxes collapse.

Bourns® power inductors are designed to provide unsurpassed performance in buck, boost and many other topologies that are found in DC/DC power converter applications.

The low DC resistance featured in many Bourns® shielded inductors are ideal for mobile electronic devices that are expected to have prolonged battery life, because of low power dissipation. The ferrite core construction helps them achieve very low core loss at high frequency. At high ripple current, Bourns® inductors allow applications to avoid unnecessary power consumption and excessive temperature rise. With magnetically-shielded construction, Bourns® power inductors help to ensure that low-level radiation will not interfere with sensitive circuits or nearby ICs.

EMI Filter Applications

Bourns® power inductors are designed to combat levels of conductive electromagnetic interference (EMI) at frequencies from the low kHz range up to a few hundred MHz. These applications can use either a single inductor or multiple LC components for enhanced attenuation. The shielded construction and the high self-resonant frequency of these inductors help to maintain a steady minimum loss of impedance over a wide frequency range.      

When used in an EMI filter application, inductors deliver a series of impedances (Z=jωL + R – see Figure 3 below) to suppress electromagnetic interference (EMI). The reactance (jωL) resists the flow of signal noise while the equivalent series resistance (R) in the inductor’s core material absorbs the undesired signal.

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Figure 3 shows the filtering performance advances made possible by the addition of a capacitor.

Inductors for Harsh Environment Applications

Bourns has developed a series of highly reliable and high-quality inductors that are compliant to the AEC-Q200 Stress Test Qualification for passive components. These inductors are suitable for automotive applications.

The Bourns® SRP-CA and SRP-FA series metal alloy powder core inductor are developed with a distributed air-gap property which can maintain a soft inductance roll-off as DC current is rising. Due to the high saturation flux density characteristic of the powder core, these inductor series are capable of retaining higher inductance at elevated DC current levels. Designed with a flat wire winding, the AEC-Q200 compliant SRP-CA and SRP-FA series inductors deliver a compact solution with exceptionally low DC and AC resistance and high saturation current up to 40 A in a compact 6 x 6 x 5 mm configuration.

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Bourns offers a series of AEC-Q200 compliant inductors that are not only designed for automotive electronics applications but are also well-suited for consumer, industrial, medical (low/medium risk)* and telecom applications where higher inductor reliability may be required.

Ensuring More Efficient Converter Designs

Contributing to more efficient converter designs, Bourns® inductors deliver the very low DCR necessary to reduce DC losses. They also offer stable inductance over a wide range of current while meeting the high operating temperature (155 °C) requirements.

Tips: in selecting the right inductor for a next-generation electronics application, start with matching the optimal inductor based on the design’s maximum output current and necessary inductance. From there, developers can choose the desired DC resistance and narrow their choices to the type of construction or coil type desired.

With 73 available non-shielded, semi-shielded, shielded and iron or metal alloy powder core high current models, Bourns offers one of the industry’s broadest lines of power inductors. Demonstrated by the line’s footprint range from 2 x 1.6 to 28 x 28 mm, heights of 0.8 to 19 mm, an inductance range from 0.1 to 4000 µH and rated current that starts at 0.2 up to 70 A, Bourns has a power inductor to suit most any electronics design.

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