There are only three basic components in any electronic circuit design- resistor, capacitor, and inductor. We have already covered the introduction to a resistor and its different types, and also covered capacitors and its different configurations. In this tutorial, we are going to know about different types of inductors and how to choose an inductor for different applications.

 

What is an Inductor?

Inductors are often referred to as "AC resistance". The main characteristic of an inductor is its ability to resist changes in current and store energy in the form of a magnetic field. The standard unit of inductance is the henry.

 

Types of Inductors

Depending on the application there are many types of inductors, they come in various form factors, there are high-frequency inductors, low-frequency power line inductors, and some specially designed inductors for decoupling and filter applications, below we will discuss different types of inductors in details.

 

Laminated Core Inductor

Construction

The elements of a laminated core inductor consist of a bobbin, a laminated core, and a coil which is wrapped around the bobbin.

To make a laminated core inductor, a wire is wrapped around the bobbin of the inductor, then the E and I plates are placed inside the bobbin one by one to form the core, this E and I sheets are made out of steel with high silicon content and its heat-treated to produce high permeability and to lower the hysteresis and eddy current losses.

Applications

• Onboard charger for Electric Vehicles
• Line and Noise Filter
• Signal’s CH and CL Filter Chokes

Example Features

• Inductance - 0.12 mHY to 100 mH
• DC Current - 1.0 ADC to 200 ADC
• Insulation System - Class B insulation, 130° C

Example Part No

• CH-100

 

Air Core Inductor

Construction

By taking a cylindrical material of specific diameter (like a drill bit) as a template, we can wrap around a length of wire to make an air-core inductor, further the inductance can be stabilized by dipping the inductor in varnish or securing it by wax.

The core material is air, so it has low permeability hence lower inductance so, it can be used for high-frequency applications.

Applications

• It is used for constructing RF tuning coils.
• The air core inductor is used in filter circuits.
• Snubber Circuit.
• It is used to ensure a lower peak inductance,
• It is used in high-frequency applications including TV and radio receivers

Example Features

• Tolerance: ± 2%
• Inductance: 0.85 mH
• Wire gauge: 18 AWG
• DC resistance: 0.44 Ohms
• Power handling: 30 Watts RMS

Example Part No

• 0807SQ-22NJLB

 

Ferrite Core Inductor

Construction

By winding a length of wire around a ferrite core will result in a ferrite core inductor. So, what is a Ferrite core and when should we use it?

Mixing Iron oxide (Fe2O3) in combination with other metal oxides like (Mn), zinc(Zn) or magnesium(Mg) at a temperature of 1000° C - 1300° C will result in a material with very interesting magnetic properties called ferrite.

Ferrite core inductors have high permeability, high electrical resistivity and low eddy current losses these characteristics make them suitable for many high-frequency applications.

Applications

• It can be used at high and medium frequencies
• It is used in switching circuit
• Pi Filters

Example Features

• Proprietary 5H and 10H ferrite materials and equivalent
• Suitable for ≥ 150 kHz range
• Operating temperature range from −25°C to +120°C
• UL 94 V–0 flame retardant rated to base and bobbin

Example Part No

• SBT-0260T
• SS21V-030930

 

Bobbin Inductor

Construction

Winding a length of wire in a specially made cylindrical bobbin and securing it with a shrink tube forms a bobbin inductor.

The core material is ferrite so, the properties are also similar to a ferrite core inductor. The small size makes them suitable for power adapter like applications.

Applications:

• SMPS circuit
• Input and output filter
• Pi Filter

Example Features

• Primary inductance standard +/- 10%
• Available in vertical types
• Dielectric strength between coil and core 0.5 KV

Example Part No

• 15104C

 

Toroidal Core Inductor

Construction

A length of wire is wrapped around a donut-shaped core is commonly known as a toroid core inductor. The core material is ferrite so, the material properties resemble a ferrite core inductor.

This type of core can contain a magnetic field very well because of its closed-loop nature, thus improving the size and inductance.

Due to the high magnetic field and high inductance value with fewer windings, the impedance is very less which helps to improve the efficiency of the inductor.

Applications

• Medical Devices
• Switching Regulators
• Industrial Controllers
• Output Filters(SMPS)

Example Features

• 560 µH ±15%  @ 10 kHz / 5 mA
• 77 mΩ ±10% (Max.)  @  Ta = 25°C

Example Part No

• MCAP115018077A-561LU

 

Axial Inductors / Colour ring inductor 

Construction

To make this type of inductor a very thin copper wire is wrapped around a dumbbell-shaped ferrite core, and two lids are connected at the top and the bottom of the dumbbell core. After that it goes through a molding process (the green material surrounding the inductor) where the values are printed as colored bands, therefore we can determine the value of the inductor just by reading the color bands and comparing them with the color code chart just like a resistor.

Applications

• Line filter
• Filter Design
• Boost Converter
• General

Example Features

• Temperature Rise - 35 °C
• Operating Temperature Range - 55 °C to +105 °C
• Storage Temperature Range - 55 °C to +105 °C
• Moisture Sensitivity Level - 1

Example Part No

• 78F101J-RC

 

Shielded Surface Mount Inductor

Construction

It is built by winding a length of wire in a cylindrical bobbin and securing it in a specially made ferrite housing forms, shielded surface mount inductor.

These inductors are specially designed for PCB mounted applications and the shielding is there to reduce EMI and noise from the inductor and also to be able to use in a high-density design.

Applications

• PDA / notebook / desktop / server applications
• High current POL converters
• Low profile, high current power supplies
• Battery-powered devices
• DC/DC converters in distributed power systems
• DC/DC converter for field-programmable gate array (FPGA)

Example Features

• Shielded construction
• Frequency range up to 5.0 MHz
• Lowest DCR/μH, in this package size
• Handles high transient current spikes without saturation
• Ultra-low buzz noise, due to composite construction

Example Part No

• IHLP-1212BZ-01

 

Wireless Charging coils

Construction

Coiling up a multi-stranded wire then putting it in a ferrite will result in a wireless charging coil.

A length of multi-stranded wire is used to reduce the skin effect, which describes a high-frequency magnetic field that can penetrate a certain depth, means if a solid wire is used in this case the most of the current will flow through the outer part of the conductor which therefore increase the resistance.

By placing a ferrite plate under a coil it can improve the inductance and can also focus the magnetic field and reduces emissions.

Applications

• Wireless Charging
• Information and communication products
• Industrial, medical and other products

Example Features

• Ls [uH] : 6.20 uH +/- 5% @100kHz 
• Rs [Ohm] : 0.095 Ω +/-10% @100kHz
• Rdc [Ohm] : 0.08 Ω

Example Part No

• WT202012-15F2-ID

 

Coupled Inductor

Construction

Winding two wires in a common core form a coupled inductor. The windings can be connected in series, parallel or as a transformer, as per application requirements, they work by transferring energy from one winding to another by mutual inductance, the most common coupled inductors have one-to-one turns ratio used in manly DC-DC converters.

Applications

• Flyback Converter
• SEPIC Converter
• Cuk Converter

Example Features

• Operating Temperature Range -50°C to +155°C
• Temperature Rise, Maximum 40°C
• Operating Frequency Up to 3MHz

Example Part No

• 76889440047

 

Multilayer Chip Inductors

Construction

The name itself indicates that it consists of multilayers. It is built by using thin plates made out of ferrite. The coil pattern is printed on it, with special metallic paste (recipe confidential to manufacturer), proper placement of these sheets a layer after another forms a coil hence inductance.

Applications

• Small Wearable Application
• Wireless LANs
• Bluetooth
• SBCs
• Motherboard

Example Features

• Operating Temperature: -55 °C to +125 °C
• Thermal Shock: -40 °C to +85 °C
• Humidity: 90 % RH at 40 °C

Example Part No

• ILSB-0805

 

Shielded Variable Inductor

Construction

By wrapping a length of wire around a hollow cylinder bobbin, and by placing and moving the core made out of ferromagnetic material or brass we can change the value of the inductor.

If the core material is ferrite, then moving the core material in the centre of the winding will increase the inductance.

If the core material is brass, then moving it to the center of the winding will decrease the inductance.

Applications

• High reliability conforms to automotive applications.
• AEC-Q200 compliant.

Example Features

• Frequency Range： 20 ～ 129 MHz
• Inductance Range： 0.05 ～ 2.7 mH
• Q Approx.： 20 ～ 60
• Highly durable against mechanical stress

Example Part No

• A1313AN-0001GGH=P3

 

So this is all about the most commonly used inductors in the Electrical and Electronics field, there are many other types of the inductor as well which are not common and are used for special purposes.