How Tank Circuit works? - Tank Circuit working principle

How Tank Circuit Works? - Tank Circuit Working Principle

Tank Circuit - Definition:

A circuit which produces electrical oscillations of any desired frequency is called as a tank circuit or oscillatory circuit.
A tank circuit consists of a parallel combination of capacitor and inductor.
In this post let us understand how does the tank circuit work in LC type oscillators?

Tank Circuit Working Principle:

To understand the tank circuit operation, consider the capacitor is already charged from a DC source with polarity as shown in the below figure.Tank_circuitHere the upper plate is positive terminal with respect to lower plate. It means there is a voltage across the capacitor and it has electrostatic energy.
When the switch SW is closed, the capacitor will start to discharge the stored energy through inductor. The current flow is indicated in the below figure.Tank_circuit_operation_1

  • Due to the nature of inductor, it will not instantly allow the entire current.
  • The current will build up slowly towards maximum value.
  • This current flow creates the magnetic field around the coil.( ie, developing electromagnetic field).
  • Eventually the electrostatic energy stored across the capacitor is converted into electromagnetic energy around the inductor.

Once the capacitor is fully discharged, the inductor’s magnetic field will start to collapse and produce counter emf. As per lenz’s law, the counter emf will keep the current flowing in the same direction as shown in the below figure.

So the capacitor will get charge in opposite polarity. Once the collapsing magnetic field has recharged the capacitor, the capacitor starts to discharge. This time the current will flow in opposite direction as shown in the below figure.The sequence of charge and discharge creates the alternating motion of electrons or an oscillating current. The energy is alternately stored in electrostatic field of capacitor and the electromagnetic field of the inductor.

  • We know that there is a resistive loss in inductor and dielectric loss in capacitor.
  • During each cycle, a small part of energy is wasted in these losses.
  • So gradually the magnitude of oscillating current will decrease and eventually it becomes zero. Ie the tank circuit will produce damped oscillations.
  • But for practical application’s we want continuous undamped oscillations.
  • To get the continuous undamped oscillations from the tank circuit, we have to supply proper amount of energy at proper intervals to the tank circuit to nullify the losses.

The frequency of oscillations in the tank circuit is decided by the values of C and L.
It is given by

f = \frac{1}{2\Pi \sqrt{LC}}

ie, If C has large value, it takes more time to charge and discharge. So the frequency will be less.
Similarly high value L, has greater opposition to the change in current flow. It leads to more time to complete each cycle.

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