Difference between Series Resonance and Parallel Resonance

Series resonance and parallel resonance are two phenomena that occur in electrical circuits containing inductors, capacitors, and resistors. They represent different ways in which circuits respond to an alternating current (AC) signal at a specific frequency.

In this article, we will understand the difference between Series resonance and parallel resonance in detail.

What is Series Resonance?

Series resonance is a phenomenon that occurs in electrical circuits containing a resistor (R), inductor (L), and capacitor (C) connected in a series. It occurs when the inductive reactance (XL) and capacitive reactance (XC) cancel each other at a specific frequency, resulting in a minimum impedance and maximum current flow through the circuit.

At resonant frequency, the inductive and capacitive reactance are equal and opposite, resulting in resonance. The resonant frequency (f) can be calculated using the formula:

[Tex]f = \frac{1}{2 \pi \sqrt{LC}}[/Tex]

where,

• f = resonant frequency (Hz)
• L = inductance (H)
• C = capacitance (F)

At resonance, the total impedance (Z) of this circuit equals to the resistance (R), resulting in minimum impedance.

Z = R

Applications of Series Resonance

Series resonance has various applications in electronics and telecommunications, including in tuning circuits, filtering, and impedance matching. It is utilized in devices such as radio receivers, oscillators, and filters to select specific frequencies or reject unwanted ones. Some common applications of series resonance are:

• Tuning circuits in radios and televisions to select specific frequencies.

• Bandwidth control in bandpass filters for communication systems.

• Power factor correction in electrical power distribution systems to improve efficiency.

• Voltage regulation in voltage stabilization circuits.

• Frequency stabilization in oscillators and frequency synthesisers.

What is Parallel Resonance?

When a resistor (R), inductor (L), and capacitor (C) are connected in parallel and the effect of the inductor cancels the effect of the capacitor at a specific supply frequency, it is called parallel resonance.

The resonant frequency of a parallel resonance circuit is the same as that of a series resonance circuit and is determined by the values of the inductance (L) and capacitance (C) according to the formula:

[Tex]f = \frac{1}{2 \pi \sqrt{LC}}[/Tex]

where,

• f = resonant frequency (Hz)
• L = inductance (H)
• C = capacitance (F)

At resonance, the circuit experiences maximum impedance, resulting in minimum current flow. Parallel resonance makes the circuit behave like a pure resistive circuit, and is utilized in various applications.

Applications of Parallel Resonance

Parallel resonance has various applications in electronics and telecommunications, including in tuning circuits, filtering, and impedance matching. It is utilized in devices such as band-pass filters, antenna circuits, and impedance matching networks. Some common applications of parallel resonance are:

• Filter circuits for removing specific frequencies in communication systems and audio equipment.

• Voltage regulation in power supplies to stabilize output voltage levels.

• Antenna tuning in radio frequency (RF) circuits for maximizing signal reception.

• Tank circuits in oscillators for generating stable oscillations at a specific frequency.

• Impedance matching in RF amplifiers and antennas to maximize power transfer.

Difference between Series Resonance and Parallel Resonance

The difference between series resonance and parallel resonance can be understood from the table given below:

Basis of difference	Series Resonance	Parallel Resonance
Definition	Series resonance occurs when a series circuit with a resistor, inductor, and capacitor cancels out the inductive and capacitive effects at a particular frequency.	Parallel resonance happens when a parallel circuit with the same components cancels out their effects at a specific supply frequency.
Impedance	At series resonance, the impedance of the series LCR circuit reaches its minimum value.	At parallel resonance, the impedance of the parallel LCR circuit reaches its maximum value.
Admittance	The series LCR circuit offers maximum admittance at series resonance.	The admittance of the parallel LCR circuit is at its minimum at parallel resonance.
Current	Series resonance results in maximum current flow through the circuit.	Parallel resonance leads to minimum current flow in the circuit.
Circuit Behaviour	At series resonance, the series LCR circuit behaves like an acceptor circuit.	At parallel resonance, the parallel LCR circuit behaves like a rejector circuit.
Magnification	Series resonance magnifies the voltage in the circuit.	Parallel resonance magnifies the current in the circuit.
Reactance	The reactances of the inductor and capacitor balance each other out, leading to a purely resistive behavior.	The reactances of the inductor and capacitor combine to create maximum opposition to current flow.
Frequency Response	Series resonance has a narrow band of frequencies where resonance occurs, making it useful for tuning specific frequencies.	Parallel resonance has a wider band of frequencies where resonance occurs, suitable for broader applications like filter circuits and antennas.
Voltage	Voltage across the circuit is at its maximum at resonance which leads to a surge in voltage.	Maximum current flows through the circuit at resonance which results in a surge in current.
Quality Factor	For series resonance, the quality factor is given by: Q = ω₀L/R	For parallel resonance, the quality factor is given by: Q = R/ω₀L
Application	Its applications include tuning, oscillator circuits, voltage amplifiers, and high-frequency filters.	Its application include current amplifiers, induction heating, filters, and radio-frequency amplifiers.

Conclusion

To conclude we can say that, series resonance occurs when the inductive and capacitive effects cancel each other out in a series circuit, resulting in maximum current flow. Parallel resonance, on the other hand, happens when the same effects cancel out in a parallel circuit, leading to minimum current flow. Each type of resonance has its own set of applications and characteristics, making them useful in various electronic circuits.

FAQs on Series and Parallel Resonance

What are the characteristics of series resonance?

The characteristics of series resonance are:

• In series resonance, the impedance of the circuit reaches its minimum value.
• The circuit behaves like a pure resistive circuit, allowing maximum current flow.

What are conditions of parallel and series resonance?

The conditions of both the resonance are:

• Parallel resonance occurs when the inductive and capacitive effects cancel each other out in a parallel circuit.
• Series resonance happens when the same effects cancel out in a series circuit.

What is the difference between series and parallel LC circuits?

The difference between both LC circuits is:

In a series LC circuit, the inductor and capacitor are connected in a series path. And in a parallel LC circuit, the inductor and capacitor are connected in parallel to each other.

How to identify series and parallel resistors?

In a series connection, resistors are connected end-to-end, forming a single path for current flow. Whereas, in a parallel connection, resistors are connected side-by-side, providing multiple paths for current flow.