The amazing facts about LC TANK CIRCUIT | Working, Applications


Hey, in this article we are going to discuss about LC Circuit or Tank Circuit or Resonant Circuit. Here we will discuss the working principle of LC tank circuit, circuit design, applications, and uses.
One of the great innovations in electronics engineering is the finding of the Tank Circuit or LC circuit which starts the telecommunication or wireless communication technology.
LC circuit is the main element of any telecommunication, tunning, oscillator circuits.


What is Tank Circuit?


The tank circuit is the simple parallel combination of a capacitor and an inductor. When a capacitor is connected in parallel across an inductor then it is called LC circuit or Tank Circuit or resonance circuit or oscillator circuit or tuned circuit.
Definitely, it is a closed-loop circuit in which continuously electrical current flow occurs due to oscillation produced by both inductor and capacitor.


Why LC Circuit is called Tank Circuit?


The name 'Tank Circuit' indicates the two properties of the LC circuit, one is storing of energy and another one is oscillation or damping. Imagine a tank with a fill of water. Now shake or nudge that tank and observe the movement of water inside the tank. You will see the water will start to slosh back and forth a lot, eventually getting quite violent.
So, the same thing happens in LC or Tank circuit, just you can imagine the current like water. Current sloshes back and forth from one side of the capacitor to the other through the inductor.


Tank Circuit Working Principle


Before you go to understand the working principle of Tank circuit, you must have clear knowledge about the properties of Inductor and Capacitor.
Now let's go to know how the LC circuit creates an oscillating signal.

First, when the circuit is connected to a DC power source, the capacitor starts charging itself, and the voltage across the capacitor also increasing. Once the capacitor fully charged and its voltage across it reaches the supply voltage connected to it, it stops taking current from the power source. 

LC Tank Circuit with power source

Now if we removed the power source, the capacitor starts discharging through the inductor. Now inductor starts storing energy in form of a magnetic field. 

LC Tank Circuit capacitor discharging

Once the voltage across the inductor is raised than the voltage across the capacitor, again inductor starts to dissipate the energy and provides energy to the capacitor to charged up in opposite polarity.

LC Tank Circuit capacitor charging

When the capacitor gets fully charged by the energy supplied by the inductor, it again starts discharging through the inductor. This whole process continuously repeated until the whole energy dissipated by the resistance of the circuit.


Signal produced by Tank Circuit


Now, we will discuss each part of the waveform of the oscillating signal produced by the LC Tank Circuit which will help you to a better understanding of the working of Tank Circuit. Here you can see the waveform in the below figure.

LC Tank Circuit signal waveform


First of all, if you observed the overall waveform, you will notice the magnitude of the waveform gradually decreased, it is because energy gradually dissipated through the internal resistance of the circuit, and at a time energy will fully dissipate then again we need to charge the circuit by an external power source.

The rising portion of the first half cycle indicates the charging of the capacitor by the external power supply and the peak point indicates, capacitor fully charged at the supply voltage level. When we remove the power supply from the circuit, the capacitor will start discharging through the inductor which indicated by the decreasing portion of the first half cycle of the waveform, and the zero point indicates that the capacitor fully discharged.

The rising portion of the negative half cycle indicates that the capacitor again starts charging in opposite polarity taking energy from the inductor and the decreasing portion indicates that the capacitor discharges. 
Next all cycles indicate the continuous repeating of the whole process until the full energy is dissipated.


Basic Concept for design of Tank Circuit


To build a Tank circuit we required only two components, inductor, and capacitor. Just connecting them in parallel we will able to make an LC tank circuit. To start the work of that circuit, first, we must charge the circuit by an external DC power supply.

In that LC Tank circuit, we can modify two parameters, one is the amplitude of the signal and another one is the frequency of the signal. We can change the amplitude of the signal by changing the voltage level of the external dc power supply.

To change the frequency of the signal we need to change the value of the inductor and capacitor. So we need the proper selection of inductor and capacitor to get the desired frequency. Remember that always non-polarised capacitor or ceramic capacitor is used to make the tank circuit.

If we required high frequency, then we need to take a lower value of capacitor and inductor because low-value capacitor provides very fastly charging and discharging property, so the time period will be less, so here we can get the high frequency.

If we required low frequency, then we need to take a high-value capacitor and inductor because a high-value capacitor takes more time to charge and discharge, so the time period will be more, so here we can get the low frequency.


Why only Ceramic Capacitor is used for LC Tank Circuit?


Already we discussed in working of the tank circuit, that capacitor connected in the tank circuit charge in opposite polarity in every cycle. Means if the capacitor got charged in positive polarity in the first cycle, it will be charged in negative polarity in the next cycle. So, as in every cycle, the direction of the current flow changing so we required a ceramic capacitor that provides the facility of both side charging. 

If we use an electrolytic capacitor, which only suitable for one side charging or in one polarity, it will not work in the tank circuit.

Other advantages of using ceramic capacitor are, 

It is available in very small value to high value.

Energy losses in the ceramic capacitor are very low.

Noise or distortion created by the ceramic capacitor also very low.


Why we must use DC supply to charge the Tank Circuit?


Now, we are going to know why we should use the DC power supply to charge the tank circuit to start its operation.
Basically, we need an external power supply to charge the capacitor connected in the tank circuit. We know that for the charging purpose of the battery or capacitor, DC power supply only required because DC has a fixed polarity which suitable for charging.
As the polarity of AC continuously changing with time, it not suitable to charge a capacitor or battery.

Another reason is, we know that capacitor gives different reactance or resistance for different frequencies. So if we use AC to charge the capacitor, it will give very low reactance or resistance, so charging not possible. But if we provide DC it will give enough resistance to the power supply to flow limited constant current and the capacitor will charge.


Application and Uses of Tank Circuit


There is a huge application of tank circuits in electronics from a very small circuit to very complex circuits. Some important applications are noted below.

1. The main element of any telecommunication circuit is the LC tank circuit because it only produces frequency for a particular communication.

2. LC tank circuit used for tuning in the signal receiver and sender circuit. It also helps to extract signals of a particular frequency from a complex signal.

3. LC tank circuit has a very important role in Audio or music production circuits.

4. LC tank circuit used in audio mixer circuit for equalizing, noise removing, echo, etc.

5. LC tank circuit also used in the electronic filter circuit.

6. Tank circuit used in modern inverter and UPS to produce proper sinusoidal waveform.

7. LC tank circuits are used in modern electronic ballast for tube light.

8. Modern wireless charging technology also uses the tank circuit for its operation.

9. Tank circuits are used in small wireless communication devices such as walkie-talkie.

10. The main part of an oscillator circuit also LC Tank Circuit.


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The amazing facts about LC TANK CIRCUIT | Working, Applications The amazing facts about LC TANK CIRCUIT | Working, Applications Reviewed by ETechnoG on 9/29/2020 Rating: 5
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