RC, LR, LC and LCR (in series) circuits

The electronics components can be divided into two categories: active components and passive components. Inductor (I), Resistor (R), and Capacitor (C) are the instances of passive components. They are being used in electronics circuits, and they may be found in practically any circuit. The RC, RL, LC, and RLC circuits are formed by combining these three components in various configurations. They have various applications, including filtering circuits, tube light chokes, and multivibrators. Thus, we will explore the fundamentals of these circuits and the theory behind them. The letter “R” is used to represent a resistor. A resistor is a component that wastes energy primarily as heat. It will have a voltage drop that will remain constant for a constant current flow.

Capacitor

The letter ‘C’ stands for the capacitor. A capacitor is a device that stores energy in the form of an electric field (temporary). A capacitor is a device that resists voltage changes. Capacitors come in various shapes and sizes, with ceramic and electrolytic capacitors being the most common. They charge in one way but discharge in the opposite.

Inductor

The letter ‘L’ is used to represent an inductor. A capacitor is similar to an inductor in that it stores energy in the form of a magnetic field. Inductors resist changes in the current. Inductors are coiled coil wires that are infrequently used compared to the first two components. When these resistors, capacitors, and inductors are combined, we can create circuits like the RL, and RLC circuits, RC coupled amplifiers, which have time and frequency-dependent responses and may be used in a variety of AC applications. An RC/RL/RLC circuit can be used as a filter, oscillator, and much more.

Basic principle of RC/RL and RLC circuits

Let us look at how a resistor, capacitor, and inductor act in an electronic circuit before moving on to the next topic. Consider a basic circuit with a capacitor and resistor in series with a power supply for the sake of comprehension (5V). When the power supply is connected to the RC circuit pair, the voltage across the resistor (V_r) increases to its maximum value while the voltage across the capacitor (V_c) remains zero. As the capacitor builds charge, the voltage across the resistor decreases and the voltage grows across the capacitor until the resistor voltage (V_r) is zero and the capacitor voltage (V_c) is maximum. RC coupling is the abbreviation for resistance-capacitance coupling. In amplifiers, this is the most common coupling approach.

Building an RC coupled amplifier with two stages

Let us talk about a two-stage RC coupled transistor amplifier circuit. Two transistors are coupled in a common emitter(CE) arrangement in the two-stage amplifier circuit, and a common power source V_CC is employed. The biassing and stabilisation network comprises the potential divider network R₁ and R₂ as well as the resistor R_e. The signal is routed through the emitter by-pass capacitor C_e, which has a low reactance.

Functioning of Circuits

The voltage across the resistor reaches its maximum when the switch is turned on, but the voltage across the capacitor remains at zero. The capacitor then charges up to the point where V_r is zero and V_c is maximum. When the switch is switched off, the capacitor discharges, resulting in a negative voltage across the resistor, and as the capacitor discharges, the capacitor and resistor voltages become zero. Inductors can be represented in the same way. When the capacitor is replaced with an inductor, the waveform will be mirrored, which means that when the switch is turned on, the voltage across the resistor (V_r) will be zero because the entire voltage will appear across the inductor (V_l). The voltage across the inductor (V_l) will reach zero as the inductor charges up, while the voltage across the resistor (V_r) will reach its maximum voltage.

RC Circuit

A capacitor and a resistor will be connected in series or parallel to a voltage or current source in the RC circuit (Resistor Capacitor Circuit). Because they are most typically utilised in filtering applications, these circuits are also known as RC networks. Low-pass, high-pass, and band-pass filters can all be constructed using an RC circuit. To make an RC circuit, we connected a load (light bulb) with a known resistance of 1k Ohms in series with a capacitor of 470uF. The circuit is powered by a 12V battery, and it is closed and opened using a switch. When the switch is turned on, the maximum voltage (12V) is applied to the resistive light bulb load (V_r), and the voltage across the capacitor is zero. When the switch is turned off, the voltage across the resistor drops to zero, and as the capacitor charges, the voltage rises to its maximum level, as illustrated in the graph.

RL Circuit

An inductor and a resistor will be connected in series or parallel in the RL Circuit (Resistor Inductor Circuit). A voltage source will drive a series RL circuit, while a current source will drive a parallel RL circuit. A first-order RL circuit with only one inductor and one capacitor is often used in passive filters.

RLC Circuit

An RLC circuit comprises a resistor, capacitor, and inductor that are linked in series or parallel. The circuit produces an oscillator circuit, which may be found in radio receivers and television sets. It is also commonly used as a damper circuit in analogue applications—a first-order RLC circuit’s resonance property.

Conclusion

Although resistors, inductors, and capacitors are common and straightforward components, when they are coupled to form circuits such as the RC/RL and RLC circuits, they display complicated behaviour that makes them appropriate for various applications. The main distinction between RC and RL circuits is that the RC coupled amplifier stores energy as an electric field, whereas the RL circuit stores energy as a magnetic field.