An inductor, also known as a reactor, is a passive component of a circuit having two terminals. This device stores energy in its magnetic field, returning it to the circuit whenever required. It was discovered that when two inductors are placed side by side without touching, the magnetic field created by the first inductor affects the second inductor. It was a crucial breakthrough that led to the invention of the first transformers.
It is probably the simplest component, comprising just a coil of copper wire. The inductance is directly proportional to the number of turns in the coil. Sometimes, however, the coil is wound around a ferromagnetic material such as iron, laminated iron, and powdered iron to increase the inductance. The shape of this core can also increase the inductance. Toroidal (donut-shaped) cores provide better inductance compared to solenoidal (rod-shaped) cores for the same number of turns. Unfortunately, it is difficult to join inductors in an integrated circuit, so they are usually replaced by resistors.
2. How Does It Work?
Whenever the current passes through a wire, it creates a magnetic field. However, the unique shape of the inductor leads to the creation of a much stronger magnetic field. This powerful magnetic field, in turn, resists alternating current, but it lets direct current flow through it. This magnetic field also stores energy.
Take a simple circuit comprising a battery, a switch, and a bulb. The bulb will glow brightly the moment you turn the switch on. Add an inductor to this circuit. As soon you turn the switch on, the bulb changes from bright to dim. On the other hand, when the switch is turned off, it becomes very bright, just for a fraction of a second before turning off completely.
As you turn the switch on, the inductor starts using the electricity to create a magnetic field, temporarily blocking the current flow. But, only DC current passes through the inductor as soon as the magnetic field is complete. That’s why the bulb changes from bright to dim. All this time, the inductor stores some electrical energy in the form of magnetic field. So, when you turn the switch off, the magnetic field keeps the current in the coil steady. Thus, the bulb burns brightly for a while before turning off.
3. Function and Significance
Though inductors are useful, it is difficult to incorporate them into electronic circuits due to their size. As they are bulkier compared to other components, they add a lot of weight and occupy plenty of space. Hence they are usually replaced by resistors in integrated circuits (ICs). Still, inductors have a wide range of industrial applications.
Filters in Tuned Circuits
One of the most common applications of inductors is to select the desired frequency in tuned circuits. They are used extensively with capacitors and resistors, either in parallel or series, to create filters. The impedance of an inductor increases as the frequency of signal increases. Thus, a stand-alone inductor can only act as a low-pass filter. However, when you combine it with a capacitor, you can create a notched filter because the impedance of a capacitor decreases as the frequency of signal increase. So, you can use different combinations of capacitors, inductors, and resistors to create various types of filters. They are found in most electronics including televisions, desktop computers, and radios.
Inductors as Chokes
If an alternate current flows through an inductor, it creates an opposite current flow. Thus, it can convert an AC supply into a DC. In other words, it chokes the AC supply but allows the DC to pass through it, hence the name ‘choke.’ Usually, they are found in power supply circuits that need to convert AC supply to DC supply.
A ferrite bead or ferrite choke is used to suppress high-frequency noise in electronic circuits. Some of the common uses of ferrite beads include computer cables, television cables, and mobile charge cables. These cables can, sometimes, act as antennas, interloping with audio and video output of your television and computer. So, inductors are used in ferrite beads to reduce such radio frequency interference.
Inductors in Proximity Sensors
Most proximity sensors work on the principle of inductance. An inductive proximity sensor comprises four parts including an inductor or coil, an oscillator, a detection circuit and an output circuit. The oscillator generates a fluctuating magnetic field. Whenever an object comes into the proximity of this magnetic field, eddy currents start to build up, reducing the sensor’s magnetic field.
The detection circuit determines the strength of the sensor, while output circuit triggers the appropriate response. Inductive proximity sensors, also called contactless sensors, are cherished for their reliability. They are used at traffic lights to detect the traffic density and also as parking sensors in cars and trucks.
An induction motor is probably the most common example of the application of inductors. Usually, in an induction motor, inductors are placed in a fixed position. In other words, they are not allowed to align with the nearby magnetic field. An AC power supply is used to create a rotating magnetic field which then rotates the shaft. The power input controls the speed of rotation. Hence, inductions motors are often used in fixed speed applications. The induction motors are very reliable and robust because there is no direct contact between the motor and the rotor.
As mentioned earlier, the discovery of inductors led to the invention of transformers, one of the fundamental components of power transmission systems. You can create a transformer by combining the inductors of a shared magnetic field. They are usually used to increase or decrease voltages of the power lines to the desired level.
Just like a capacitor, an inductor can also store energy. However, unlike a capacitor, it can store energy for a limited time. As the energy is stored in a magnetic field, it collapses as soon as the power supply is removed. Still, inductors function as reliable energy storage device in switch mode power supply such as desktop computers.