PASSIVE SOLUTIONS

Surface-Mountable PTC Thermistors

PTC thermistors from EPCOS provide reliable and cost-effective solutions in a wide variety of applications. They are used, for example, as resettable fuses in telecommunications equipment and power supplies, as temperature and level sensors, and for temperature compensation in LED applications. PTCs in space-saving SMD sizes are gaining importance in many fields.

Temperature Sensors

PTC thermistors from EPCOS are thermally sensitive resistors whose electrical resistance rapidly increases when a defined temperature (reference temperature) is exceeded. They are used in lighting applications, household appliances, safety systems such as automotive airbags and tyre pressure control systems, and as temperature sensors in laptop computer power supplies. Apart from customary 0805 devices, EPCOS now also offers surface-mountable PTCs in 0603 for sensor applications. The reference temperature tolerance of these new miniature PTC thermistors (B59601A0xx5B062 series) has been reduced from ± 5°C, the previous standard, to as low as ± 3°C.

EPCOS is expanding its portfolio with even smaller SMD sizes and further reduced response time. A new sensor series in EIA size 0402 has been established. Samples are available with a sensing temperature of 115°C (B59401A0115A062 series). Production is scheduled to start in January 2007.

Temperature Compensation



Due to their thermal sensitivity and resistance characteristics, PTC thermistors are ideal for temperature compensation in LED applications. The use of PTCs allows designers to achieve remarkable improvements in LED luminosity and brightness for backlighting of mobile phones, laptop computer displays and automotive LCD displays.

With rising temperature the thermistor's resistance increases, causing the LED driver to reduce current according to the corresponding LED specifications/derating characteristics. Operating the LEDs at their limit results in a higher luminosity, thus enabling designers to minimise the number of LEDs.

Overcurrent Protection

The range of PTC thermistors from EPCOS also includes PTC devices designed for overcurrent protection. Commonly called resettable fuses (or simply resettables), PTC-based overcurrent protection devices are a very attractive alternative compared to traditional fuses. Normal system operation continues after the fault has been rectified, without any part replacement or maintenance work. In contrast to other available solutions, ceramic-based PTCs will return to their initial resistance value within a few minutes, even though the maximum allowable stress has been applied. To handle higher currents EPCOS offers wired PTC resettables. Especially for low-current applications, surface-mountable versions are the preferred choice. EPCOS has extended its overcurrent protection offerings with SMD PTCs specified for continuous operation at voltages of up to 265V (B59807A0090A062 series). They are available in size 1210 for currents up to 15mA. Previous SMD PTCs were limited to nominal voltages of only 80V.

Protection of Telecommunications Equipment



PTCs play an important role for overcurrent protection measures in telecommunications equipment such as MDF modules, modems or other networking devices. To protect the symmetrical wires reliably, two PTC thermistors with nearly identical temperature/resistance characteristics are necessary. EPCOS' TPPs (Telecom Pair Protectors) contain a pair of optimised PTCs featuring minimum resistance tolerances in a single SMD package. The TPPs are compliant with relevant standards, e.g. ITU-T K.30 and UL 94V-0. The latest TPP device is housed in a smaller package measuring just 9.9mm x 8.75mm x 7.2mm (B596xxT1120A062 series).

These are just a few examples of the wide range of PTC thermistor applications. EPCOS offers PTC products for virtually every application and can also provide customised solutions.

Features

• Thermally sensitive resistors
• Reference temperature down to just ±3°C
• 0402 Sensor series now available
• Ceramic and wired PTC resettables
• Continuous operation to 265V
• Telecom Pair Protector featuring 2x PTCs available

Applications

• Overcurrent protection
• Telecommunications
• Degaussing
• Heating elements
• Motor starting
• Sensors
• Switching applications

For further information, including Datasheets for a variety of applications as mentioned above, please click here