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Series resonance vs parallel resonance-difference between Series resonance and parallel resonance

This page on Series resonance vs parallel resonance describes difference between Series resonance and parallel resonance. It also mentions what is resonance condition in electronic circuit.

When alternating voltage is applied to a circuit which contains capacitor and coil, response of the circuit is maximum when applied voltage frequency is equal to natural frequency of the circuit. The form of electrical response depends on whether the capacitor(C) and inductor coil (L) are connected in series or parallel.

If the components are connected in series as shown in figure-1, the condition is referred as series resonance and circuit is known as series resonant circuit. If the components are connected in parallel as shown in figure-2, the condition is referred as parallel resonance and circuit is known as parallel resonant circuit.

In other words:
In AC circuits, a condition in which inductive reactance becomes exactly equal to capacitive reactance is referred as resonance.

XL = XC
➨ 2*πf*L = [ 1/{ (2*π)* (f*C)0.5 } ]
➨ Z = { R2 + ( XL - XC )2 }0.5

Resonance Frequency

In a circuit consisting of L and C components, the frequency at which resonance occurs is called resonance frequency.

➨Fr = 1 / { (2*π)*(L*C)0.5 }
Where,
Fr = resonant frequency or resonance frequency
L = Inductance in henrys
C = Capacitance in Farads

Series resonant circuit

series resonance circuit

A series L-C circuit in which magnitudes of capacitive and inductive reactances are exactly equal is known as series resonant circuit as mentioned above. It is also known as acceptor circuit.

Characteristics of series resonance circuit:
• Minimum impedance
• Maximum circuit current
• cos(φ) = 1 , hence current and voltage becomes in phase.
• Circuit current becomes proportional to circuit resistance i.e. I ~ 1/R

Uses of series resonance circuit:
• As frequency selection circuit in radio and TV tuner circuits.
• As band pass filter circuit.

Circuit Q or Q factor

Ratio of inductive reactance to the resistance is called circuit-Q. It is known as magnification factor.
➨ Q = XL/R
Where,
Q = circuit-Q, unitless
XL = inductive reactance, Ohm
R = circuit resistance, Ohm
Selectivity is proportional to Q.

Bandwidth of Resonance Curve

F2-F1 = R/(2*π*L)
Where,
F2 = Upper frequency of bandwidth (Hertz)
F1 =Lower frequency of bandwidth (Hertz)
R = circuit resistance, Ohm
L = Inductance , Henrys

parallel resonant circuit

parallel resonance circuit

A parallel L-C circuit in which magnitudes of capacitive and inductive reactances are exactly equal is known as parallel resonant circuit as mentioned above. It is also known as rejector circuit.

Characteristics of parallel resonance circuit:
• Maximum impedance
• Minimum circuit current
• cos(φ) = 1, hence voltage and current becomes in phase
• Circuit current depends on circuit impedance, Z = L/C or I ~ -(1/R)

Uses of parallel resonance circuit:
• As a Band Stop Filter
• As a tank circuit in Oscillators
• As a plate load in IF and RF amplifiers
• As I.F. trap in aerial circuit of radio as well as TV receivers.


Following table mention comparison between series resonance circuit and parallel resonance circuit.

Specifications Series resonance
circuit
Parallel resonance
circuit
Impedance at
resonance
Manimum Maximum
Current at
resonance
Maximum Minimum
Effective
impedance
R L/CR
Resonant
frequency
1/(2*π*(LC)0.5) (1/2*π)*{(1/LC)- R2/L2}0.5
It magnifies Voltage Current
It is known as Acceptor circuit Rejector circuit
Power Factor Unity Unity

This difference between acceptor and rejector circuit is useful to understand comparison between the both.

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