Non-linear electric circuit components – examples and characteristics

Date of publication: 01-02-2024 Update date: 10-04-2026 🕒 5 min read

Circuits comprise various components, each of them playing a specific role in the electric current flow. Basic components include conductors, resistors, voltage sources, diodes, transistors, switches, displays, sensors, etc. Some of them can be described as linear, and other as non-linear circuit components. In this article, the latter group is described.

What is a non-linear component?
Electronic non-linear component types
Differences between linear and non-linear components
Electronic non-linear component applications

Non-linear electric circuit components – characteristics

Non-linear electric circuit components are elements demonstrating a non-linear characteristic in relation to voltage or current. It means that the flowing current is not proportional to its voltage value, unlike in the case with linear components. The relationship between these parameters (A and V) cannot be described here by a simple mathematical equation, again, unlike in the case of linear electric circuit components.

Non-linear electric circuit components can demonstrate various characteristics. Moreover, some are controllable and other, unfortunately, are not. They are crucial for electronic circuit designers, as they facilitate implementing a variety of functions, such as rectification, signal amplification, voltage stabilisation, etc. These would be impossible to achieve if the designer applied only linear components, e.g. resistors or capacitors.

Examples of non-linear components of electric circuits

As we have already mentioned above, there is a multitude of non-linear electric circuit components. This article presents just the most essential and most commonly used components that every electronic engineering fan will come across, sooner or later.

Solid-state (semiconductor) diode: a component demonstrating a non-linear current-voltage characteristic, which means that the current flow in this component depends on the bias (current flow direction) and is not proportional to its voltage. Diodes are commonly used as rectifying circuit elements.
Bipolar transistor, NPN and PNP: This component demonstrates a non-linear current characteristic depending on the voltage applied to its three terminals (base, collector, emitter). Bipolar transistors are often used as signal amplifiers.
Unipolar transistor (MOSFET type): MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) transistors also demonstrate a non-linear current-voltage characteristic and are widely used both in digital and analogue systems.
Thermistors: components whose resistance changes in relation to temperature. This basic property makes them perfectly suitable for temperature control systems.
Zener diodes: these components are a variation of solid-state diodes. They are characterised by precisely defined breakdown voltage which, despite its rapid (burst-like) impact, does not result in their damage. Such diodes are used for voltage stabilisation purposes.

What is the difference between non-linear and linear electric circuit components?

Non-linear electric circuit components differ from the linear ones primarily in terms of their current-voltage characteristic. In a nutshell, the current flowing through them is not proportional to the voltage or current value, and this characteristic makes them suitable for performing more advanced operations and signal transformations. Furthermore, non-linear elements are essential to operate numerous advanced functions in electronic engineering, while linear elements are used in less complex applications. However, it is worth delving deeper into this issue and pointing out some other differences that either result from the above-mentioned property or complement it in some way.

Current-voltage characteristic:

In linear components, such as resistors, capacitors and coils, current is proportional to voltage in the component, as per the Ohm’s law, i.e. A = V/R. The linearity of this characteristic results in the fact that any voltage adjustment results in a proportional current change.
In the case of non-linear components, e.g. diodes and transistors, current is not constantly proportional to voltage, and their behaviour can be more complex and depends on many different factors.

Energy transmission:

Linear components do not generate new frequencies when transmitting energy, nor do they transform existing frequencies in the circuit. Thus, they transmit energy without affecting it in any way.
Non-linear components are able to generate new frequency harmonics, transform signals and introduce non-linear distortions. A diode in a rectifier circuit that converts an alternating signal into a unidirectional signal is a good example of this.

Applications:

Linear components are commonly used in simple circuits, such as voltage dividers, passive filters, etc.
Non-linear components are used in more advanced electronic circuits, such as amplifiers, rectifying systems, voltage stabilisers/regulators, modulators and demodulators, i.e. in all applications requiring complex signal processing.

Adjustment and control:

Linear components are typically not capable of actively adjusting or controlling current or voltage in a circuit.
Non-linear components can be used for active adjustment and control of electric signals in circuits. A transistor is a good example, as it can operate as an amplifier or a switch.

Examples of non-linear electric circuit component applications

Non-linear electric circuit components are widely used in various fields of electronic and technical engineering. See below for a few application examples.

Diode rectifiers: Solid-state diodes are used to convert AC signals into DC signals in power supply circuits, such as switched-mode power supply modules, etc. They convert AC signals into DC signals, which is an essential feature for most electronic devices.
Operational amplifiers: These amplifiers (op-amps) are non-linear components constituting the basis for various amplifier, filter and oscillator systems in electronic engineering. They are used to amplify signals and perform a number of mathematical operations related to electric signals.
Modulation and demodulation: Transistors and diodes are used in modulation and demodulation circuits that are vital in telecommunications. The examples of these applications include amplitude modulation (AM) and frequency modulation (FM) in radio sets.
Voltage stabilisers/regulators: Zener diodes and transistors can be used in stabilising systems which maintain voltage on a constant level, regardless of changes in input voltage or load.
Keying and switching: Transistors often operate as switches in digital circuits and controllers. Depending on the input signal, they can control the current flow in a circuit.
Electronic thermometers: Due to their non-linear temperature-related resistance characteristic, thermistors are used as temperature sensors in various applications, e.g. electronic thermometers.
Light-emitting diodes (LED): LEDs are solid-state diodes which emit light as a result of current flow. They are commonly used as light sources in displays, pointers and in an array of home, office or industrial illumination systems.
Tunnel diodes: These diodes are designed on the basis of the tunnel effect discovered by Leo Esaki, a Japanese Nobel prize winner. They are used in various systems, such as microwave generators and diode clocks.
Quartz oscillators: Quartz oscillators are equipped with quartz crystals and non-linear components to generate precise time signals, which is necessary, for example, to ensure correct operation of numerous real-time clocks (RTC), i.e. both quartz watches and microcontrollers.
Photodetectors: Photodetectors generally use diodes or other non-linear elements to convert light into electric signals. They are used in optoelectronic applications such as fibre-optic receivers and light sensors.

The above are just some examples of non-linear electric circuit component applications. Their diverse character and capabilities make them an integral part of modern electronic systems, and it is really difficult to imagine the operation of the latter without them.

Finally, note also that even if just one of the electronic circuit parts has a non-linear characteristic, this circuit cannot be referred to as a linear one. In a linear circuit, the condition of linearity must be fulfilled for each component.

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