Tag Archives: Power Inductors

Is Metal Better than Ferrite for Inductors?

Many power and signal conditioning applications use power inductors as a basic component to store, block, filter, or attenuate energy. Today’s power circuits use increasingly higher switching frequencies and high powers that impose challenges in packaging and material levels for component manufacturers. Consequently, power inductors, while shrinking their form factors, are pushing to provide higher-rated currents.

The above presents a dual challenge to component manufacturers and designers alike. For instance, component designers must use materials other than the traditional ferrite core materials to miniaturize these devices, while maintaining other parameters such as DCR and inductance without change. Taiyo Yuden is meeting the dynamic challenges of these applications by using metal for power inductors.

Engineers typically select power inductors primarily by their inductance value, then by their current rating and DCR or DC resistance value, followed by their operating temperature range. They may also consider whether the inductor will require to have shielding or none. The application circuit that will use the inductor requires optimization of the above parameters.

Applications of power inductors can range from filtering EMI at the AC inputs of a power supply to filtering ripples at the output of a DC power supply. Inductors are indispensable for reducing the ripple in voltage and current in switching power supply outputs. DC-DC converters use inductors for their self-inductance property of storing power—as the switching circuit turns off, the inductor discharges its stored current. Almost all types of voltage regulation circuits, for instance, power supplies, DC-DC converters, switching circuits, and others, take advantage of the characteristics of power inductors.

Semiconductor power supplies are transitioning from the higher 3.3 V rails and lower currents to lower voltages of 1-1.2 V rails and higher currents for catering to advances in chip design technology. This entails the need for a high-current handling power inductor. Furthermore, smaller form factors of enclosures following the development of smaller-sized electronic components are increasing the demand for miniaturization of all associated electronic components, including the power inductor.

However, the size of power inductors and their higher current capability present a tradeoff. Withstanding higher currents typically requires a bigger case size, resulting in a change in land patterns on PCBs. On the other hand, a small size translates into saturation current due to insufficient inductance. Taiyo Yuden uses the patented construction of a wire-wound multilayer power inductor with a unique metal alloy. This construction allows the designer to achieve both the required inductance in a small case size and a high saturation current.

Taiyo Yuden create their multilayer inductor by printing a pattern on a ceramic sheet that contains ferrite. They laminate these sheets before firing them. Then they assemble the final piece, pressure bond them and fire them. At the last stage, they form external electrodes at both ends. The use of material with a high magnetic permeability results in an inductor with a high inductance value.

The construction of wire-wound inductors follows the traditional method. The coil is either on the inside or on the outside surface of a magnetic material, such as ferrite. A high number of turns results in a higher inductance and a higher DC resistance.

Difference Between Power and RF Inductors

In many electronic designs, we have components that consist of only several turns of a wire, with or without a core. These components are inductors. It is customary to find them in many types of electronic devices, including voltage and power conversion circuits to high-frequency microwave and RF circuits. Typically, inductors resist any change in the current flowing through them, by producing an electromagnetic field.

Available in a variety of package styles depending on their current ratings, inductors are essential components in electronic designs. They function as filters, chokes, and impedance-matching functions. For a practical application, it is essential to understand the important performance parameters of inductors.

Any inductor, whether used for power or RF applications, has the same performance parameters. These include the inductance value, its tolerance, current rating, its DC resistance, SRF or self-resonant frequency, Q or quality factor, and temperature range. However, specific applications may stress more on some of these performance parameters as they have more relevance for that application. For instance, an application involving RF frequencies may give more importance to Q and SRF parameters rather than to the current rating, which is more important for power applications.

The size of an inductor—how big or how small it can be—is usually dependent on the inductance value, its current carrying capacity, and acceptable losses. These are critical parameters when selecting inductors. Selecting an inductor usually begins with the inductance value, typically in nH or in mH, and depends on its function in the circuit. Associated with the nominal inductance value is its tolerance, in %, characterizing the amount of variation of the inductance value, and is determined by the application.

For instance, RF applications typically require inductances closely matched by precise inductance values, and with tight tolerances, such as ±2%. On the other hand, power applications may use inductors with inductance values within a larger band, and with wider tolerances, such as ±20%.

Another important parameter for inductors is their ability to handle current, which can vary greatly by application. This is specifically true for inductors in power circuits such as DC-DC converters, where the current values can change widely, with very high peak-to-average current ratios. Inductors selected on the basis of the application’s highest instantaneous current value may provide an inductor much larger than necessary. On the other hand, selecting an inductor based on the average current value in the circuit may lead to a small inductor resulting in inconsistent performance during peak current deliveries.

The quality of an inductor has more relevance in RF circuits than it has for power applications. Quality or the Q factor is a dimensionless parameter that characterizes the inductor’s bandwidth relative to its center frequency. High Q values are typically matched to narrow bandwidths and low losses, more critical in RF applications.

For power applications, the losses in inductors are more important. Here, the DC losses, characterized by the resistance of the wire, are rather more relevant. Therefore, inductors for power applications tend to be made of wires with larger diameters, so as to increase the area for current travel and thereby reduce the resistance.