Power Inductors and Storage Chokes

Switched-mode power supplies are becoming ever more widespread. The semiconductor manufacturers have made their contribution, offering a wide range these integrated circuits with simplified circuit design. Care must be taken in the selection of the appropriate power inductor storage choke to fully utilize the advantages of switching regulators.

In this article the terms power inductor and storage choke are used almost interchangeably. In the context of switched‑mode power supplies they both denote inductors that primarily store energy in their magnetic field and control current ripple in the power path. “Storage choke” emphasises the energy‑buffering role in series with the load or switching node, while “power inductor” is the more general term used in datasheets and catalogues for inductors designed for higher currents and switching applications.

Term	Typical usage in this article	Main emphasis
Storage choke	Inductor in the energy‑storing path of a SMPS (e.g. buck, boost, SEPIC)	Energy buffering and current ripple control in switching converters
Power inductor	General catalogue term for inductors used in power electronics	Current rating, losses, core technology and package for switching and DC/DC applications
Line / EMI suppression choke	Choke placed in series with supply lines, often on toroidal or common‑mode cores	Impedance to differential‑ or common‑mode noise for EMC compliance, not primarily energy storage

Note: The specific series names and example curves shown in this article (e.g. WE‑SI, WE‑PD, WE‑HC, WE‑DD and selected metal‑composite families) are representative examples only. Equivalent components are available from multiple manufacturers with comparable core materials and electrical characteristics.

Power Inductors Calculations

The selection of cores and windings of storage chokes are optimized for use in switching converters and DC-DC converters.

Leading manufacturers of storage chokes following recommendations from various switching converter IC manufacturers, e.g. National Semiconductor, Linear Technology, STMicroelectronics, Texas Instruments, Exar, Diodes, MPS, ON Semiconductor, Semtech, Maxim and a special customized solutions can be found in their reference design guidelines.

Toroidal Core Types

Toroidal storage chokes are ideal from the EMC perspective: The magnetic field lines mainly pass through the core. The stray field and associated coupling in neighboring conductor tracks or components remain small.

In the field of switching converters, storage chokes serve to buffer electrical energy and, at the same time, to smooth the output current. The energy stored in the core in this process is:

energy stored in storage choke inductor eq. 1.

To enable high energy storage and to minimize the resulting core losses, the toroidal core volume is divided into many electrically isolated regions. The iron powder used in our storage chokes therefore has three-dimensional, uniformly distributed, microscopic air gaps, which prevent eddy-current losses.

The disadvantage of reduced permeability is balanced by greater maximum energy storage and lower losses. Furthermore, these cores are extremely well suited for use in applications with high DC premagnetization.

Data book specifications

Open-circuit inductance L₀:

If the inductor is operated without DC premagnetization or with only a small AC current, the open-circuit inductance L₀ results.This value may be measured with sufficiently sensitive inductance measuring equipment for small AC voltages e.g. 0.1–0.5 V and a fixed measuring frequency between 1 kHz and 100 kHz, depending on the inductance value.

Inductance rating L_N:

In addition to the small AC voltage amplitude, the specified DC current is superimposed and the resulting inductance measured.

Current rating I_N:

The DC current, for which the inductance and wire thickness are specified and whose specifications are optimized. As shown in graph on Figure 2., inductance only saturates with a much larger current.

DC resistance DCR:

The windings resistance value is measured with an ohmmeter at an ambient temperature of +25 °C.The test current for resistance measurement is a small DC current, which does not lead to a significant temperature increase in the wire. As values in the milliohm range are measured here, a 4-wire measurement must be made to minimize measurement errors.

Magnetic field energy E:

The energy, for which the core data and windings of the coil is optimized. This is specified in microjoules.The following simple and practically proven formulae can be used for dimensioning a storage choke. A brief extract from the extensive core material program and the following table should provide an overview of the choke dimensioning process. Depending on the application, further specifications from the core material data spectrum may be necessary.

Iron core material data:

The table 1. shows an overview of the most commonly used materials and their applications.

Operating temperature:

The operating temperature of the iron powder core may be from –55 °C to +125 °C. Prolonged core operation above +75 °C however results in increased losses.

Insulation voltage:

The protective coating of the toroidal core uniquely identifies the core material and serves to protect against environmental effects and provides electrical isolation from the windings. Epoxy resin coatings are used and an insulation dielectric strength of 500 VDC is achieved as standard. Higher insulation voltages can also be offered.

A_L value: For every size of core an A_L value is specified to simply calculate the winding turns for the required choke; the tolerance is ±10%.
The standard means of measuring the A_L value is at B = 1 mT and f = 10 kHz.

Storage Choke Calculation:

The following demonstrates how a storage choke can be calculated for a switching converter application:
Example: switching converter (step-down controller – storage choke)

Requirements:

Inductance rating L_N = 100 µH Current rating (DC) I_N = 1 A Peak current through the inductance I_max = 1.5 A Ripple current = 20% of I_max = 0.3 A (see Chapter III/Applications) Switching frequency f = 52 kHz

A maximum AC flux density B_AC = 0.05 T is recommended for iron powder cores (to ensure low core losses). Also the inductance should be selected so the ripple current does not exceed 20%–30% of the maximum current.

Step 1 : Choice of the core material and the necessary core volume (V). As the switching frequency is just 50 kHz, we firstly select the material 3W7538 with µ_r = 75.

Selected core: 3W7538, as switching frequency < 70 kHz; core no. 13 d_a = 12.7 mm; d_i = 7.7 mm; h = 4.83 mm

Magnetic data: l = 3.19 cm; A = 0.112 cm2; V = 0.358 cm3 A_L value: 33 nH/N²

Step 2: Required winding turns

The final number of winding turns must be increased as a result of current dependent permeability. The correction factor for the A_L value is determined from the “effective permeability against DC premagnetization” graph (see Figure 3.).

At H = 1724 A/m on the graph in Figure 3. → Effective permeability with DC premagnetization = 80% of the initial permeability.

To be certain that the full inductance rating of 100µH exists with a DC current of 1A, the final number of winding turns is calculated as:

Step 3: Determination of the DC resistance

The wire diameter can be ascertained from the relevant wire tables for the required current of 1A, e.g. AWG 22 (d = 0.6 mm). This limits the self-heating of the wire to less than +10°C.

The DC resistance of the windings is given by:

Step 4: Check for max. AC field flux density

Step 5: Calculation of core losses

The losses in the core material may be calculated from the following formula:

For our examples this leads to:

The total losses of the storage choke are low at around 370mW and the choke calculated is well suited for the application.

High Current Inductor Types

SMD NiZn Ferrite Core Storage Choke

SMD storage chokes with highly dynamic and low loss NiZn ferrite cores are suitable as chokes in switching control applications up to a clock frequency of approx. 10MHz and offer high current loading capacity and low DC resistances.

There are a multitude of construction types available for the different types of application:

• Magnetically shielded series
• Unshielded versions series

Data book specifications

Inductance L: Different measurement conditions apply for the different construction series. The inductance is stated at a certain test frequency and measurement voltage (see data sheet).

Current rating IN: The current rating of the inductor is specified as the DC current at which inductor exceeds the permitted tolerance limits (DL) or the self generated heating (DT) exceeds a certain limit. The smaller of the currents defined by the two conditions is termed the current rating of the inductor. This is how ever not the saturation current, which is higher than the current rating.

DC resistance DCR: The windings resistance value is measured with an ohmmeter at an ambient temperature of +20 °C. The test current for resistance measurement is a small DC current, which does not lead to a significant temperature increase in the wire. As values in the milliohm range are measured here, a 4-wire measurement must be made to minimize measurement errors.

Operating temperature: The ambient temperature when operating the SMD NiZn series of storage chokes at full current rating load should generally range from –40 °C to +85 °C. The self-heating of the component must be taken into account at higher ambient temperatures in order that the permissible solder joint temperature is not exceeded or the wire insulation damaged. The wire used can withstand a temperature of up to +150 °C. The ferrite core itself may be used over a far greater temperature range (approx. –50 °C to +250 °C [Curie temperature]). However, in this case, the tolerance limits of the inductor may be exceeded due to the temperature dependence of permeability.

Operating temperature = ambient temperature + self-heating < +125 ºC

The above curve on Figure 5. assumes that self-heating is permissible up to a maximum temperature sum (component + ambient temperature) of +125 °C. The current must be reduced above an ambient temperature of +85 °C. The curve below is intended for critical applications, in which the coil itself should only generate a small amount of self-heating.

Insulation resistance: The insulation resistance between windings and coil core is more than 100 MΩ for a test voltage of 500 V_DC_DC.

Saturation current I_sat: The saturation current is the DC current at which the zero current inductance is reduced by a certain percentage.

The percentage of inductance decrease is however not standardised and can be defined differently for each package type. In datasheets – and especially when comparing data from different manufacturers – very close attention must be paid to the definition point. A printout of the measurement curve “Inductance versus DC premagnetization” is better still. Here the user can, for example, check in detail how the inductor behaves in the case of overload or at the moment it switches on. An example for a standardised curve is shown in Figure 6.

Volt-µsec product: As a result of their effective magnetic area A_eff, storage chokes can only be driven to a maximum value – the so-called Volt-µsec product. The following calculation rule applies for the step-down controller to determine the necessary Vµsec product of storage chokes:

With increasing switching frequency, the necessary Vµsec product of the storage choke becomes lower; however, with increasing input voltage it becomes higher. This relationship is again illustrated in Figure 2.48 below.

Practical tips:

For some types in the SMD NiZn SMD chokes manufacturers also provide Vµsec specification in their datasheets. If this information is missing, it can be read off from the measurement curve “Inductance versus DC current premagnetization”. Here you locate the inductance plateau where you read off the associated current and residual inductance values and calculate the Vµsec product as follows:

Ferrite storage chokes

For ferrites, the saturation curve shows a very steep decline beyond a certain DC current value (“hard saturation”). For this reason it is recommended to reduce the Vµsec product calculated in this way and therefore to then optimise inductor selection.

Iron powder core storage chokes, Superflux, WE-PERM etc. have a constant decrease in inductance due to the DC-premagnetization (soft saturation). As a rule:

When to use NiZn SMD chokes versus iron powder

In practice, SMD NiZn ferrite storage chokes are particularly well suited for:

• Low to medium current DC/DC converters with switching frequencies from a few hundred kHz up to several MHz.
• Space‑constrained designs where a low profile, magnetically shielded SMD footprint is more important than absolute energy storage.
• Noise‑sensitive environments (e.g. point‑of‑load regulators on digital boards) where reduced stray field is critical for EMC and signal integrity.

Toroidal iron powder storage chokes are typically preferred when:

• Large energy storage is needed at relatively modest switching frequencies (tens of kHz to low hundreds of kHz).
• The design benefits from soft saturation behaviour and gradual inductance reduction with DC bias.
• Through‑hole mounting, high current capability and very low external field are acceptable or advantageous, for example in industrial power stages or EMI suppression.

This helps to frame the detailed NiZn and iron powder characteristics in terms of concrete converter design choices.

NiZn storage choke core material parameters

Power Loss and Temperature Increase in the Component

Now the power loss can be approximately determined, the question arises of the temperature rise of the component in operation. Measurement curves can be generated for the rise in temperature of the components with DC currents. Here the questions are to be resolved:

How was the component measured?

1. mounted on a PCB with a lot of copper (= cooling element!) OR
2. only the component via a thin and poor heat-conducting connection

After what time was the temperature read off from the component (thermal time constant !)

The following approximation formulas can be useful in the design phase; however they do not obviate measurement under real operating conditions. Determination of total power loss in the storage choke:

Temperature increase in the component (large surface)

NiZn Power Ferrite Core Double Chokes

NiZn power ferrite core double chokes (Figure 9.) with two separate windings expand the standard spectrum of storage chokes with more features.

Features:

Two separate windings on a common ferrite core

• Available in a 1 : 1 winding (standard), but also in other winding ratios (customer-specific)
• Bifilar winding for minimal stray inductance / high coupling factor • (k ~ 0.985 … 0.990) or separate layer winding with increased leakage inductance
• Operating voltage up to 80V_DC
• Isolation voltage 100V_DC max

Applications:

• SEPIC switching controllers (functional principle – see Chapter III/7.4)
• CUK switching controller (switching controller with negative output voltage)
• Switching controllers with second, unregulated output voltage (auxiliary voltage)

Operating temperature:

The ambient temperature of double choke under full rated current load is usually between –40 °C and +85 °C. The self-heating of the component must be taken into account at higher ambient temperatures in order that the permissible solder joint temperature is not exceeded or the wire insulation damaged.

The wire used can withstand a temperature of up to +150 °C. The ferrite core itself may be used over a far greater temperature range (approx. –50 °C to +250 °C [Curie temperature]). However, in this case, the inductance tolerance limits may be exceeded due to the temperature dependence of permeability.

Electrical characteristics

Rated current: The self-heating for the pair of windings passing maximum current should not sum to more than +40°C. This is a conservative number, datasheet specification may differ per type and manufacturer.

Rated current is determined for each winding, which passes current on its own, leading to a temperature increase of up to +20 °C and is specified as IN1 and IN2 respectively. If both windings pass their rated current at the same time, this leads to self-heating totaling +40 °C.

DC resistance: Correspondingly, the specification for the winding resistance of the two individual windings is found from individual measurements. Attention: Please compare the datasheet specifications carefully – often the parallel configuration of the two windings is found in the literature as rated current / DC resistance, which suggests a higher rated current and lower DC resistance. In practice this is of course, not the application for this series of chokes!

Saturation current: In the case of the double choke with the same inductance, it is sufficient if just one of the windings carries the saturation current. The second winding is inevitably reduced in its inductance. The value is identical for the same inductance; the saturation current per winding is specified for dissimilar inductance values.

TPC “Tiny Power Choke“ SMD storage chokes

TPC “Tiny Power Choke“ of storage chokes (Figure 10.) is usually for applications for which the packing density and the package height is important. This design enable to produce the smallest wire-wound inductors in dimensions such as 2.8 x 2.8 x 1.0 mm.

These chokes are mostly used for switching controllers that have several outputs integrated in one IC, e.g. LTC3544B. (Figure 11.) This IC has 4 outputs at which different voltages, output currents and switching frequencies are adjustable.

The core material used is typically NiZn and is therefore suitable for switching frequencies up to 10 MHz. The saturation current is defined as a –35% inductance drop in relation to the zero current inductance, which is usually typical for inductance in this small package. Magnetically shielded versions as on Figure 10. are suitable for switching controllers for example in mobile applications.

SMD High-Current Inductors

Laptop computers and motherboards of modern computers are equipped with processors, whose clock frequencies may be 1 GHz or more. Processor manufacturers rely on low supply voltages in order to maintain losses in integrated circuits within tolerable limits and to attain the required switching speeds. These lie between 1 … 3.3 Volts depending on the processor generation.

Components require large currents at the same time. Current inputs of up to 60A per processor are not a rarity and cannot be handled by well known switching regulators. The so-called multiphase switching converters fulfill the intelligent power management concept required. Because of the high switching frequency and the output current requirements, one needs only small inductance with high current capability and low losses. SMD high-current inductors are suitable for these applications.

The core material used for high current inductors may require high-purity alloy of various types of iron powders, which shows significantly lower core losses than conventional iron powder cores.

Thermal aging: Thermal aging can lead to the destruction of the organic binder used, especially at high operating temperatures with standard iron powder material. A thermal avalanche effect can consequently occur, which may finally destroy the core material. For standard iron powder materials and those not thermally treated for reasons of their production process, the rule of thumb applies that the maximum temperature of +125 °C measured at the component should not be exceeded for a prolonged period. Nevertheless, modern materials with practically no thermal aging are now also available by leading manufacturers.

The core material of high current inductors can withstand high temperatures up to +200°C or even higher.

Flat wire types. High current inductors can use a rectangular flat wire, which proves to be a major advantage over conventional round wire designs in terms of AC resistance loss. A flat wire (Figure 13.) inside the choke is used in place of the conventional round wire.

Flat wire windings offer the following advantages:

Large wire surface – thus low high-frequency losses (skin effect)

• Low winding capacity – hence high self-resonant frequency
• Low DC resistance – thus low self-heating at high prolonged currents
• High packing density and therefore smaller component size than comparable chokes with round wire (Figure 2.57)
• High operating temperature up to max. +150 °C

Through the combination of low-loss core material and flat wire windings inside the core, achievable performance of SMD high-current inductors can be:

• Small SMD component size such as 6.6 x 7.3 mm2, 10.5 x 10.0 mm2 or 13.5 x 12.8 mm2 with a height of 3.4 mm to max. 4.9 mm.
• Open-circuit inductance L₀, tested at 100 MHz with 0.25 VAC
• Inductance rating L_N at current rating I_N and self-heating < +50 °C
• Min. inductance at max. current I_max and self-heating < +100 °C
• Min. DC windings resistance DCR_max at Ta = +25 °C

Figure 15. shows the typical behavior of SMD high-current inductor 0.82 µH choke 13.2 x 12.8 x 6.2 mm.

The component has an inductance of 0.65 µH at the specified rated current of 27 A and demonstrates typical self-heating of +50 °C. The inductance is very stable under current load; the limiting factor is the self-heating of the component. Even at a current load of 50 A the inductance does not drop more than 30% from the open-circuit inductance. The self-heating is well over +100 °C, however.

Flat wire, low core loss inductors represents a highly dynamic and robust types of storage chokes, especially suited for use in high-current switching converters and multiphase or polyphase converters. Additional application areas are in high-current interference suppression chokes and as a replacement for rod core chokes.

Comparison of common power inductor families

The following overview summarises typical characteristics of the main storage choke families discussed in this article.

Inductor family	Typical frequency range	Saturation behaviour	DC bias / inductance trend	EMI and stray field	Mechanical robustness	Typical applications
Toroidal iron powder storage choke	~20 kHz – 300 kHz	Soft saturation	Gradual inductance decrease with DC current, high usable energy	Very low stray field due to closed magnetic path	Good; through‑hole mounting, epoxy‑coated core	Energy storage in offline SMPS, PFC chokes, high‑current DC filtering, radio interference suppression
SMD NiZn ferrite storage choke (shielded / unshielded)	~100 kHz – 10 MHz	Hard saturation	Inductance relatively constant up to a defined DC bias, then sharp drop	Shielded versions offer low stray field; unshielded versions higher EMI but lower cost	Moderate; SMD package, sensitive to shock compared to composites	General‑purpose DC/DC converters, POL regulators, RF‑friendly power rails
NiZn double chokes (two windings on common core)	~100 kHz – few MHz	Ferrite hard saturation on overloaded winding	Strong coupling between windings; saturation of one winding affects the other	Shielded constructions offer good EMI, suitable for compact layouts	Similar to SMD NiZn storage chokes	SEPIC and Ćuk converters, auxiliary supply rails, multi‑output converters
Tiny Power Choke (TPC) SMD	~1 MHz – 10 MHz	Hard saturation	Inductance drop dominated by small core and high current density	Shielded miniaturised packages reduce coupling into nearby traces	Mechanically modest but optimised for dense handheld / mobile layouts	Multi‑output low‑power DC/DCs in mobile and portable equipment, camera and RF modules
SMD high‑current, flat‑wire inductors	~100 kHz – few MHz	Soft to moderate saturation, depending on core alloy	Very stable inductance over a wide current range, low DCR	Typically shielded; designed to minimise both copper and core losses	High; robust construction, often with high thermal rating	Multiphase VRMs for CPUs/GPUs/AI accelerators, high‑current POLs, high‑efficiency server and telecom converters
Radio interference suppression toroidal chokes	~25 kHz – 30 MHz (impedance role)	Soft saturation in normal operation region	Selected for impedance versus frequency rather than energy storage	Very low stray field; designed to present high impedance to differential‑mode noise	Good; toroidal, through‑hole, often potted	Differential‑mode EMI suppression at converter input/output, filters in industrial and automotive power lines
Metal composite power inductors	~100 kHz – several MHz	Soft saturation with high saturation flux density	Excellent DC bias behaviour with minimal inductance droop, good over temperature	Very low leakage flux due to monolithic, gapless construction	Very high; vibration resistance up to tens of g, well suited for harsh environment	High‑current automotive ECUs, industrial motor drives, compact high‑efficiency DC/DCs, replacement for ferrite and iron powder where size and robustness matter

Radio Interference Suppression Choke

In contrast to the energy‑storing power inductors and storage chokes discussed so far, the “choke” in this section is used in the EMI sense, where the component is optimised for impedance to conducted noise rather than for bulk energy storage.

Radio interference suppression chokes use usually iron powder toroidal cores with a very low stray field. High current loading capacity is achieved through high saturation magnetization. The useable maximum upper frequency range of this component extends from a few MHz to approx. 30 MHz depending on the type.

The impedance-phase curve against frequency of a typical toroidal core choke is shown in Figures 16. and 17.

It may be seen from Figure 17. that the resonant frequency is at 4.1 MHz. Above 4.1 MHz the capacitive character of the choke predominates, at 30 MHz the impedance has fallen to approx. 200 Ω. The impedance is almost linear (Figure 16.) up to the resonant frequency of 4.1 MHz.

Due to the frequency dependence of complex permeability, calculations are only feasible in limited frequency bandwidths and sufficiently far (in the linear range) below the resonant frequency. Figure 18. shows the equivalent circuit of the choke in the 25 kHz to 1 MHz range, Figure 19. the equivalent circuit in the 1 MHz to 5 MHz range. The values were found using an impedance analyzer, calculating on the basis of the components’ equivalent circuit. Due to high non-linearity, the equivalent circuit can be simulated over a wide frequency range with just 3 components.

From the measurement curves impedance and phase an increase in eddy-current losses and a decrease in the complex permeability can be seen.

the impedance can be calculated as a function of frequency. The broken line in Figures 18. and 19. are the simulated curves with the values given by the equivalent circuits. It shows that without considering the complex permeability and its frequency dependence, the calculation can be performed with limited accuracy.

Practical tip:

Here another word on the saturation of the ferrite ring: The effective core cross-sectional area is inversely proportional to the saturation current and proportional to the impedance. This means that wherever possible, the larger core cross-section area should be chosen.

High‑frequency and wide‑bandgap trends

With the growing adoption of GaN and SiC switches, many new converter designs are moving to higher switching frequencies in order to shrink magnetics and capacitors. This trend shifts the inductor design trade‑off: core materials with lower losses at several hundred kHz to MHz, excellent DC bias performance and predictable temperature behaviour (such as optimised ferrites and modern metal composite alloys) become increasingly attractive, while legacy iron powder solutions may reach their loss and temperature limits sooner. When evaluating inductor families for such converters, it is therefore essential to consider not just inductance and current rating, but also the full loss versus frequency and temperature profile of the chosen core material.

Metal Composite Inductors

Latest metal composite inductors (Figure 20.) come with a remarkably higher energy density compared to the ferrite inductors. This leads to 30% – 50% smaller case sizes which, for example, serves the trend for downsizing high current ECU power circuits. Furthermore, smaller case sizes also have the pleasant side-effect of being less prone to get damaged in harsh or vibrating environments. A true plus in terms of long term reliability.

DC Bias Characteristics

Excellent magnetic saturation characteristics of metal composite inductors (i.e. Ferrite core = 0.4T vs. Metal Composite Type = above 1.5T) render it difficult to magnetically saturate, which in turn is resulting in good inductance vs. current performance, without a substantial drop off. In comparison, ferrite inductors do not only suffer from a fairly quicker inductance drop off.

Their inductance also suffers the undesirable effect that it varies with temperature, whereas the performance of their metal composite counterparts is stable over the entire specified temperature range. Naturally, the qualification of applications using ferrite inductors needs increased effort compared to metal composite inductors due to consideration of different temperature ranges.

Low loss characteristics of metal composite vs ferrite inductors assist realization of high efficiency power circuits such as ECU and makes thermal design considerations simple.

High Mechanical Shock and Vibration Robustness

Ferrite inductors consist of several sintered parts being constructively composed with an air gap inside the body, whereas metal composite inductors are based on a monolithic design without air gap.

Due to that assembled structure, the ferrite types’ resistance to vibrations is limited to <4G to maximum 10G. Opposed to that, the monolithic structure of the metal composite inductors leads to a significantly higher vibration resistance – up to 50G, depending on the inductor type. This may be advantage for harsh environmental, high vibration applications such as automotive, industrial or aerospace/defense electronics.

In automotive and other mission‑profile‑driven designs, this high vibration resistance combines with stable inductance over temperature to simplify worst‑case analysis of the power stage. Instead of having to consider strong temperature‑dependent inductance reduction and limited g‑ratings, designers can focus on thermal management and lifetime under elevated ambient conditions, making metal composite devices attractive candidates for safety‑relevant ECUs and long‑life industrial controllers.

Low EMI Noise

Also in terms of a lower leakage flux outside the power inductors, the point goes to the metal composite types: Their monolithic structure causes by far less leakage as the magnetic flux simply is concentrated inside the inductor housing. See figure 23.

Summary

Storage chokes and power inductors are key energy‑buffering elements in switched‑mode power supplies, determining ripple, efficiency and dynamic behaviour of the converter. Their design starts from electrical requirements (topology, ripple, frequency, current), proceeds through core selection and winding design, and must be verified against loss, temperature rise and DC‑bias characteristics.

Toroidal iron powder chokes offer high usable energy and soft saturation for lower‑frequency, high‑current applications, whereas SMD NiZn ferrite and Tiny Power Choke families target compact, high‑frequency DC/DC converters with tight EMI constraints. Flat‑wire high‑current inductors and metal composite types address modern multiphase VRMs and automotive or industrial ECUs, combining low losses, high current capability and robust mechanical performance.

Understanding how inductance, core material, construction type and datasheet curves interact allows designers to select suitable inductors for applications ranging from simple buck converters up to GaN/SiC‑based high‑frequency power stages.The formulas, examples and comparison table in this article provide a practical toolkit for interpreting inductor data and narrowing down appropriate component families for real‑world designs.

FAQ

Further Read:

For detailed step‑by‑step guidance on turning the concepts and formulas in this article into a concrete inductor choice for a given converter design, see also: Selection of the Storage Inductors for DC/DC Converters. That companion article focuses on practical selection criteria, while the present text provides the underlying magnetic and construction fundamentals.