What is an RLC circuit

An RLC circuit is an electrical system made up of resistors, coils or inductors, and capacitors connected together. These circuits can operate with both direct current and alternating current, although their most interesting behaviour is observed with AC, where phenomena such as resonance and phase shift between current and voltage appear. With DC, the circuit mainly shows transient charge and discharge phenomena, which help to understand how resistance, inductance and capacitance interact. RLC circuits are fundamental for studying oscillating systems and are widely used in electronics, telecommunications and other technological fields.

Operation of RLC circuits

The operation of an RLC circuit depends on the interaction between resistance, inductance and capacitance, especially when alternating current is applied. These three elements determine how the current flows, how energy is stored and released, and how the circuit responds to different frequencies. In addition, they allow the appearance of phenomena such as resonance and damping of oscillations, concepts fundamental to understanding their behaviour in electronics and telecommunications.

Fundamental parameters

RLC circuits are made up of three essential elements: resistance (R), inductance (L) and capacitance (C). The resistance limits the current intensity, dissipating energy as heat. The inductance, associated with the coil, generates a magnetic field and causes a delay in the current’s response to voltage changes. The capacitance, provided by the capacitor, allows electrical energy to be stored and released later, also affecting the phase shift between current and voltage. The interaction of these three parameters determines the overall behaviour of the circuit when faced with alternating current signals.

Resonance in RLC circuits

Resonance occurs when the frequency of the applied signal coincides with the natural frequency of the circuit, causing the amplitude of the current to reach its maximum value. At this point, the inductive and capacitive reactance cancel each other out, leaving only resistance as opposition to the passage of current. The resonance frequency depends on the values of L and C and is a key concept for designing filters, oscillators and tuning systems in electronics.

Behaviour with alternating current

When an RLC circuit is connected to an alternating current source, the current and voltage are not always in phase due to the presence of inductance and capacitance. The phase difference depends on the signal frequency and the values of the components. The total impedance of the circuit combines the resistance with inductive and capacitive reactances, determining both the amplitude of the current and its phase shift. This behaviour is fundamental for analysing the response of electrical systems to different frequencies.

Types of RLC circuits

There are mainly three configurations: series, parallel and combined. In a series RLC circuit, the components are connected one after another, sharing the same current but with varying voltage across each element. In a parallel RLC, the components are connected between two common points, sharing the same voltage and with individual currents in each branch. Combined circuits show mixed characteristics. Each type has specific applications: series circuits are used in simple filters and oscillators, while parallel ones are employed in tuners and frequency selection systems.

Applications of RLC circuits

RLC circuits are widely used in electronics and telecommunications due to their ability to filter, tune and temporarily store energy. They are used in frequency filters, oscillators, resonant circuits for radio and television, and control systems where it is necessary to adjust the response to specific alternating signals. Understanding these applications allows you to connect theory with practical uses in real life and modern technological devices.