PTC device is a resettable overcurrent circuit protection device commonly used in applications where sensitive components are at risk of overcurrent. The ability of PTC devices to reset after exposure to overcurrent conditions is an attractive feature in circuits that are difficult for users or technicians to access or require constant normal operating time. PTC devices come in surface mount, radial lead, and battery strip (axial lead) versions. The telecommunications version offers surface mount and radial lead packaging. Littelfuse uses Polyswitch ? And Polyfuse ? The brand offers a full range of PTC devices.

Circuit breakers are mechanical overcurrent protection devices. When excessive current flows through the equipment, they will trip or open circuit. Circuit breakers are used to protect a wide range of equipment and systems, such as motors, transformers, telecommunications equipment, computer industrial automation, air conditioning, power distribution, variable speed drives, intelligent control panels, and other industrial equipment systems. They are also used for low-voltage battery powered distribution circuits in heavy vehicles, automobiles, ships, airplanes, and off-road vehicles. There are three basic types of circuit breakers.

The hydraulic magnetic circuit breaker has an electromagnetic coil, an iron core sealed in a pipeline filled with hydraulic fluid, a spring-loaded actuator, and two electrical contacts,. When the excessive current generated by overload flows through the device, the electromagnetic field in the coil will increase, causing the iron core to pass through the tube and tripping the spring loaded actuator, thereby breaking the contacts and disconnecting the circuit. The opening speed is determined by the viscosity or thickness of the hydraulic oil.

The thermal circuit breaker is tripped by a thermal sensitive bimetallic strip. The heat generated by current overload deforms the metal strip and trips the actuator, causing the circuit to disconnect.

In a short-circuit state, use electromagnetic circuit breakers and thermal current circuit breakers to disconnect bimetallic wires.

MLV and MOV varistors are voltage sensitive devices used to protect circuits from transient voltage surges. Surface mount resistors use ceramic multilayer structures (MLVs) to protect circuit boards in small electronic products from transient effects caused by electrostatic discharge (ESD), inductive loads, switches, and lightning surge residues. Metal oxide varistors (MOVs) are epoxy resin encapsulated zinc oxide disk radial or axial leads. MOV is a mid-range device used to protect small machinery, power supplies, and components. Industrial MOVs are larger rigid terminals, with installation devices made of zinc oxide discs encapsulated in epoxy polymer shells to provide complete electrical isolation. Industrial MOVs are used for high-energy industrial applications.

Sensors include reed switches, reed sensors, reed relays, Hall effect sensors, temperature sensing thermistors, and resistive temperature detectors. Typical applications include sensing of proximity, liquid level, liquid flow rate, velocity, and temperature.

A thyristor is a solid-state switch in a normally open (high impedance) circuit that can withstand the rated blocking voltage until it is triggered to the on state. Once triggered, the thyristor becomes a low impedance current path until the main current stops or drops below the minimum holding current. Thyristors are typically two or three terminal devices used in unidirectional or bidirectional circuit configurations. Controllable silicon is a unidirectional device. A bidirectional thyristor is a bidirectional device. Thyristors are commonly used in household appliances such as lighting (dimmer switches), heating and temperature control, alarm activation, and fan speed control. They can also be used for power tools to control actions such as motor speed, nail events, or battery charging. Outdoor equipment, including sprinkler systems, gas engine ignition devices, electronic display screens, area lighting, and sports equipment, also use thyristors.

TVS diode is a discrete, fast switching semiconductor device that can respond to overvoltage events faster than most other types of circuit protection devices. TVS diodes have low clamp voltage transient characteristics, such as lightning, induced load switching, and electrostatic discharge. TVS stands for Discrete Transient Voltage Suppression. They can be used for various applications, such as protecting data and signal lines, microprocessors, MOS memory, and AC power lines. The industries that typically use television diodes are telecommunications and industrial equipment, computers, peripheral devices, and consumer electronics.