Application Of Ptc Thermistor In Lithium Battery

By Author: RachelAnne
Total Articles: 2
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Compared with NiCd or NiMH batteries, polymer batteries (that is, lithium-ion batteries) have unique advantages such as large electric capacity per unit volume, large current density, fast charging, small size, light weight, and high conversion efficiency. They’re not only widely used in various portable equipment, mobile devices, but also can be used in medical devices, industry, agriculture, defense, transportation and other fields.

However, in the actual application of lithium-ion batteries, there are quite strict requirements on conditions such as charging, discharging, and high-temperature environments. When the voltage across the battery is too high during the charging, it will increase the danger of leakage, smoke, combustion, and explosion of the battery. Overcharging may be caused by uncontrollable charging, incorrect electrodes or incorrect use of the charger. When the lithium-ion battery has an excessive charging or discharging current or an external short circuit, internal heating may damage the battery or burn other components, which will seriously shorten the service life of the battery; Similarly, if ...
... the lithium-ion battery works in a high-temperature environment or encounters a load, the high current will increase the internal temperature of the lithium-ion battery, which will also increase the risk of battery leakage, smoke, combustion, and burst.

Therefore, lithium-ion batteries must be designed with a dedicated battery management circuit. All lithium-ion battery management circuits include functions of overcharge and overdischarge termination control without protection against overcurrent, overtemperature, and short circuits. Therefore, the function of protection circuit is to monitor the parameters of the battery charge and discharge status for various faults that may occur in the battery to ensure the battery life and efficiency, and to prevent the battery and external equipment from being damaged.
Polymer PTC thermistor products have outstanding advantages in overcurrent, overtemperature, and short-circuit protection of high-current-density lithium-ion batteries and their management circuits. Polymer PTC thermistors are also called self-resetting overload protectors or self-resetting fuse, which can complete over current, over temperature, short circuit protection with only a single component. It has an irreplaceable and essential role in the protection application of lithium-ion batteries and their management circuits.

Lithium-ion battery management and protection circuits are usually a primary protection circuit consisting of a dedicated integrated IC and a metal oxide semiconductor field-effect transistor(MOSFET). The protection IC controls the on or off of the FET by monitoring the voltage across the battery and the discharge current to prevent faults such as overcharge, short circuit, and overdischarge. Although primary protection is generally considered to be reliable, the protection IC or MOS-FET may be damaged when the electrostatic discharge voltage or temperature is too high, and the integrated circuit will oscillate during a short circuit. Most of the detection of the charge, discharge and over current of the IC + MOSFET circuits is indirect, which does not guarantee that overcurrent protection will be provided in all working states of the battery, thus reducing the reliability of the protection. After the polymer PTC thermistor is connected to the protection circuit, even if the protection circuit fails or the temperature rise is high, PTC can still provide timely protection for faults such as overcharge, overcurrent, short circuit, and overtemperature to ensure that safety problems such as explosion and battery damage will not occur when the battery is misused, abused reversely connected or shorted.

If you find it interesting and informative, here is another good article about the basics of NTC thermistors http://www.kynixsemiconductor.com/News/101.html. Click for further reading:)

An editor working in electron industry.