Introduction of Non-Linear Resistors

Non-Linear Resistors

Non-linear resistors are electronic components that do not follow Ohm's law, meaning their resistance changes with variations in voltage, current, or temperature. This characteristic makes them useful in various applications where a dynamic response is required.

Construction of Non-Linear Resistors

The construction of non-linear resistors varies depending on the type and intended application:

Thermistors

These are made from semiconductor materials such as metal oxides of manganese, cobalt, nickel, and strontium. The materials are typically doped and then pressed into a desired shape, such as rods, discs, or beads, before being sintered. The terminals are either inserted into the resistor body or soldered to metallized surfaces.

Varistors

Varistors are constructed using metal oxide materials like zinc oxide or silicon carbide. These materials are sintered to form a solid body with a non-linear voltage-current characteristic. The structure allows for significant changes in resistance with voltage.

Photoresistors (LDRs)

These are made from photoconductive materials such as cadmium sulfide or lead sulfide. The materials are processed to form a thin film or bead that changes resistance in response to light intensity.

Features of Non-Linear Resistors

Non-linear resistors possess several key features that distinguish them from linear resistors:

Variable Resistance

Their resistance changes with external stimuli such as voltage, temperature, or light, allowing them to perform functions like voltage regulation, temperature sensing, and light detection.

Protection and Safety

Varistors, for example, can protect circuits from voltage surges by clamping the voltage to a safe level.

Sensitivity

Thermistors are highly sensitive to temperature changes, making them ideal for precise temperature measurements and control.

Types of Non-Linear Resistors

There are several types of non-linear resistors, each with unique characteristics and applications:

Thermistors

These are temperature-dependent resistors. There are two main types:Negative Temperature Coefficient (NTC) Thermistors: The resistance decreases as temperature increases. They are used in temperature sensing and compensation circuits.Positive Temperature Coefficient (PTC) Thermistors: The resistance increases with temperature. They are used for current limiting and self-resetting fuses.

Varistors

Also known as voltage-dependent resistors (VDRs), varistors are used to protect circuits from voltage surges. They are commonly used in power supplies and electronic devices to clamp voltage spikes.

Photoresistors (LDRs)

These resistors change their resistance based on the intensity of light. They are used in light-sensitive applications such as automatic lighting controls and solar panel systems.

Non-Linear Resistors in Panasonic

Multilayer SMD Varistors

Multilayer SMD Varistors are monolithic, ceramic devices.  Multilayer SMD Varistors protect against damage from electrostatic discharge (ESD).

Panasonic offers multilayer versions of SMD Varistors. They are available in Surface Mount packages and have a wide range of Varistor voltages and peak current/energy capabilities.

NTC SMD Thermistors

NTC (Negative Temperature Coefficient) SMD Thermistors are multilayer devices that inversely change resistance value according to temperature. NTC SMD Thermistors detect, measure or compensate for temperature. For example, these Thermistors can be used to monitor battery charging to sense when the battery is fully charged.

Panasonic offers Surface Mount NTC Thermistors in a wide selection of values. Panasonic’s Thermistors are excellent in temperature detection and compensation applications and are small, lightweight and suitable for high density placement.

ESD Suppressor

ESD Suppressors are devices that excel at suppressing electrostatic noise within a system. ESD Suppressors are used to protect electronic devices from high static surges using their ability to rapidly decrease resistance value to encourage the flow of electricity to go to ground.

Panasonic ESD Suppressors are available with a wide range of specifications. Panasonic’s ESD Suppressors have excellent electrostatic-noise suppression and ESD withstanding characteristics. They are available in small sizes, are lightweight, have low capacitance loading and high peak voltage handling capabilities.

Metal Oxide Varistors (MOV) / ZNR (Zinc Oxide Non-Linear Resistor)

ZNR stands for Zinc Oxide Non-linear Resistor. MOV devices are used to protect electronic equipment against voltage transients and surges. For example, a ZNR can protect circuits against a surge, such as lightning. The equivalent electrical circuit of the MOV would be back-to back Zener Diodes and a parallel connected Capacitor, that’s one MOV doing the job of three components. Metal Oxide Varistors can save board space and cost.

Panasonic discovered the ZNR Surge Absorber function in 1968 and was a pioneer in the use of Zinc Oxide as a Surge Absorber. Panasonic Metal Oxide Varistors are one of the top brands of Surge Absorbers and have been for over 40 years.

Applications of Non-Linear Resistors

Non-linear resistors are used in a wide range of applications due to their unique properties:

Surge Protection

Varistors are extensively used in surge protectors to safeguard electronic equipment from voltage spikes caused by lightning or power line disturbances.

Temperature Sensing and Control

Thermistors are used in temperature sensors, thermostats, and temperature compensation circuits in various electronic devices, including computers and appliances.

Light Sensing

Photoresistors are used in light-sensitive applications such as automatic street lights, solar panel systems, and light meters.

Audio and Signal Processing

Non-linear resistors can be used in audio circuits to introduce controlled distortion or in signal processing to limit signal amplitude.

Principle of Non-Linear Resistors

The principle of operation for non-linear resistors is based on the material properties and physical structure that lead to a non-linear relationship between voltage, current, or temperature:

• Thermistors: The resistance change is due to the temperature-dependent properties of the semiconductor material. As temperature changes, the number of charge carriers in the material changes, leading to a change in resistance.
• Varistors: The non-linear behavior is due to the metal oxide material's ability to change its resistance based on the applied voltage. At low voltages, the resistance is high, but when the voltage exceeds a certain threshold, the resistance drops sharply, allowing the surge current to flow through and be dissipated.
• Photoresistors: The resistance change is due to the photoconductive material's response to light. When light falls on the surface, it generates charge carriers, reducing the resistance.

Conclusion

Non-linear resistors are essential components in modern electronics due to their ability to provide dynamic responses to various stimuli. Their construction, features, types, applications, and principles make them indispensable in circuit design, protection, and sensing applications. Understanding their behavior and applications is crucial for optimizing electronic systems and ensuring their reliability.

Frequently Ask Questions

Is an incandescent lamp a non-linear resistor?

Even though it’s a resistive device, an incandescent lamp keeps a pretty high power factor. But, if we look closer, the resistance in an incandescent lamp isn’t exactly linear. This has been checked experimentally using some lab instruments.

Is a thermistor a non-linear resistor?

Yep! Just like the BaTiO3 thermistor, this thing has a highly non-linear resistance/temperature response. It’s super useful for thermal control or regulating circuits, but not so much for temperature measurement. Also, apart from just limiting current in circuits, we can make self-limiting heaters out of wires or strips, and those work great for heat tracing.

What’s an example of a non-linear circuit?

There are a bunch of non-linear electronic components, like diodes, transistors, and even iron core inductors and transformers when their cores get saturated. Non-linear circuits include things like mixers, modulators, rectifiers, radio receiver detectors, and digital logic circuits.

Is RTD linear or nonlinear?

RTDs are mostly linear. They're way more linear than thermocouples, but they do have a small second-order nonlinearity of around 0.38% for every 100°C of the measurement range (see Figure 1). People usually fix this nonlinearity with digital correction, though in many cases, you can also handle it with pure analog processing and linearization.

Is a varistor linear or nonlinear?

A varistor (also called a voltage-dependent resistor or VDR) is a surge-protecting component, and its resistance changes depending on the applied voltage. It’s definitely non-linear, with a current-voltage curve that’s a lot like what you see in a diode.

What’s the difference between linear and non-linear circuits?

In linear circuits, the current is directly proportional to the voltage applied, which means if you double the voltage, you double the current. In non-linear circuits, though, the relationship between input and output isn’t a straight line. For example, take a typical pn diode—the current flowing through it is an exponential function of the voltage across it.

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