What’s the PTC of the li-polymer battery, and what’s the function? How does it work and protect the li-polymer battery?

The PTC (Positive Temperature Coefficient) thermistor is a critical safety component often found in Li-Polymer (Lithium Polymer) battery packs. It functions as a protective device that responds to temperature changes.

Function of the PTC in Li-Polymer Batteries:

  1. Overcurrent and Short Circuit Protection: The primary function of a PTC in Li-Polymer batteries is to protect against overcurrent and short circuit conditions. When a large current flows through the li-polymer battery, either due to a malfunction in the device it powers or a short circuit, the temperature of the li-polymer battery increases.
  2. Temperature Sensitivity: Unlike regular resistors, a PTC thermistor’s resistance increases as the temperature rises. This characteristic is leveraged to protect the li-polymer battery in abnormal conditions.

How the PTC Works:

  1. Regular Operation: Under normal operating conditions, the PTC has a low resistance, generally allowing the li-polymer battery to function without significant power loss.
  2. Response to Excessive Current: In the event of overcurrent or a short circuit, the current flowing through the li-polymer battery increases significantly. This leads to a rise in the temperature of the PTC thermistor.
  3. Resistance Increase: The PTC’s resistance increases rapidly as the temperature rises. This increase in resistance limits the current flowing through the li-polymer battery, reducing the risk of overheating, which can lead to li-polymer battery damage or even safety hazards like fires or explosions.
  4. Automatic Reset: Once the overcurrent condition ceases and the temperature drops, the PTC cools down, and its resistance decreases back to a low level, allowing regular li-polymer battery operation to resume. This automatic reset feature is a significant advantage of PTC thermistors.
  5. Complementary Protection: The PTC thermistor is usually used in conjunction with other protective components, such as a Protection Circuit Module (PCM) or a Li-Polymer Battery Management System (BMS), which provides overcharge, over-discharge, and short-circuit protection.

Protective Role of PTC:

Including a PTC in a Li-Polymer battery pack enhances overall safety by providing a responsive and self-resetting protective measure against excessive current and overheating. It’s an essential component for preventing thermal runaway – a dangerous condition where increasing temperature leads to further increases in temperature, potentially leading to li-polymer battery failure or combustion.

In summary, the PTC thermistor in a Li-Polymer battery acts as a temperature-dependent current limiter, ensuring safer li-polymer battery operation, especially under fault conditions like overcurrent and short circuits.


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