Together with the development of the IoT sector and the digitisation of industrial automation systems, manufacturers of controllers and communication network components have been looking for precise, durable, but also small-sized protective components. Littelfuse is one of the leading suppliers of such solutions.
Recently, the TME product range has been extended to include a number of Littelfuse components, i.e. varistors, thermistors, protectors and inductors. In this article, we want to familiarise our clients with the new range of products, as it is characterised by high quality and a wide range of parameters. Note also that all presented products are available in, e.g. SMD packages, i.e. in formats designed for the mass production of electronic circuits. These solutions and their capabilities will surely catch the eye of professionals involved in industrial automation systems, building automation systems and related fields.
This article covers the following issues:
- Design and applications of newly marketed varistors
- Overview of the Littelfuse measuring thermistors
- Brand-name overvoltage protectors
- Inductors and coils for the protection of communication ports
Varistors
The essential property of varistors is the change in resistance depending on the voltage present between their leads. They are protection elements incorporated in equipment with various power ratings, not only in electronic devices, but also in industrial machinery and even heavy-duty equipment (e.g. drilling rigs). Littelfuse supplies several types of varistors, differing primarily in design, but also in their related characteristics, so the assortment is truly diverse and covers the full range of typical applications.
The largest group of varistors that are available in the TME product catalogue includes THT components, i.e. items designed for through-hole assembly. Their voltage rating ranges from 8.5 V to 1.65 kV (their maximum instantaneous current can even reach 75 kA). They are designed mostly for AC circuits operating at the voltage ranging from 4 V to 1 kV. In DC equipment, the maximum continuous potential difference at the leads can range from 5.5 V to 1.2 kV (note that at least 10% tolerance over these values should be maintained to avoid component wear). Thermal tolerance of most THT components ranges from -55°C to 85°C, however, selected elements can operate even at 125°C.
The SMD varistors operate within an equally wide range of parameters, thanks to which they can be used in devices such as industrial controllers, frequency converters or charging controllers in energy storage banks. The components are housed in 0402–2220 packages. They can be used at even 2.8 kV AC and 3.5 kV DC (note, however, that, for the majority of models, the rating does not exceed 575 V and 730 V, respectively).
The final group of varistors that have been recently introduced in the TME product catalogue includes block components equipped with mounting holes and connectors (DB series) or screw terminals (DA, BA, BB series). These products are designed for heavy industry applications (mining, refineries and transport).
Measuring thermistors
The TME product catalogue features new NTC (negative temperature coefficient) thermistors whose resistance decreases in parallel with the increase in temperature. These are typical measuring components, used as thermal sensors in equipment where temperature control requires relative precision and must be provided over a wide range of values. The components provided by this manufacturer are mostly designed as THT (through-hole assembly) elements, including the TO220-2 format with a mounting hole and metal surface facilitating mounting on heat sinks and other elements requiring temperature monitoring. Our product range also includes models equipped with a copper clip, models housed in DO-35 packages and SMD thermistors. Their operating temperature ranges from -55–80°C to -200–600°C, and their maximum resistance range is 500 Ω–5 MΩ.
TO103J2K
TO-220 packages facilitate mounting with good thermal conductivity values.
Overvoltage protectors
Typical overvoltage protector applications include circuits for equipment connected to large communication networks, e.g. ADSL modems, as well as measurement, laboratory and medical equipment.. They are also used in antennas and their connectors to discharge currents resulting from voltage spikes. Such interferences can be caused by a number of uncontrollable causes, e.g. malfunctions and random accidents, but, above all, by electrostatic discharges (ESD). In such cases, a protector significantly mitigates the circuit damage risk. Littelfuse offers protectors in through-hole assembly and surface-mounted versions. The ignition voltage (steep resistance drop) ranges from 75 V to 7.5 kV – these are therefore application-specific components, but the wide assortment meets the requirements of numerous diverse applications. Pulse currents that will not result in permanent protector damage reach even 20 kA.
SMD inductors
The TME product catalogue also includes SMD filter inductors manufactured by Littelfuse. These are ceramic, (common-mode) input filter elements used to isolate communication systems from interferences, e.g. ESDs. They are used in mobile devices (phones, tablets) and IoT equipment, most commonly within USB and HDMI port lines, etc. The coils are designed in the multilayer technology, which results in their smallest possible sizes with necessary inductance ratings retained. The components are housed in standard SMD packages, i.e. from 0202 to 1008. Despite their compact size, the components withstand currents reaching 4.8 A.
