CR1625 battery.Popular science: mobile phone battery protection circuit

　　This article mainly introduces the protection circuit of mobile phone batteries. We all always make various misoperations when using batteries, and the cells of mobile phone batteries are actually relatively fragile, so complete protection measures are essential for a qualified mobile phone battery. The following is the text:

　　1. Protection of nickel-metal hydride batteries

　　The protection device for mobile phone nickel-metal hydride batteries is very simple. It is the flat ribbon-like thing in the picture that spans between two cells. It is called a recoverable fuse, also known as pTC, which stands for Positive Temperature Coefficient Thermistor. The English abbreviation for resistance. In the circuit, it is connected in series in the power supply circuit. Once a large current (such as a short circuit) occurs, its own resistance value will be rapidly increased due to its pTC effect, which will act as a circuit breaker.

　　2. Introduction to pTC

　　pTC positive temperature coefficient thermistor, also known as polyswitch polymer resettable fuse (polymerresettablefuse). Polymer resettable fuses are composed of a polymer matrix and carbon black particles that make it conductive. Because polymer resettable fuses are conductors, current will flow through them. When an overcurrent passes through a polymer resettable fuse, the heat generated (which is I2R) will cause it to expand. As a result, the carbon black particles will separate and the resistance of the polymer resettable fuse will increase. This will cause the polymer resettable fuse to generate heat faster and expand more, further increasing the resistance. When the temperature reaches 125°C, the resistance changes significantly, causing the current to decrease significantly. The small current flowing through the polymer resettable fuse at this time is enough to keep it at this temperature and in a high resistance state. When the fault is cleared, the polymer resettable fuse shrinks back to its original shape, reconnecting the carbon black particles, thereby reducing the resistance to a level with a specified holding current. The above process can be repeated multiple times. The protection principle of pTC is as follows:

　　The cold pTC resistance value is only tens of milliohms, while the hot resistance value can reach hundreds of kiloohms.

　　3. Lithium-ion battery protection circuit

　　This article mainly explains with illustrations.

　　The left side of the picture shows the schematic diagram of a typical lithium-ion protection circuit. B+ and B- represent the typical positive and negative electrodes, while p+ and p- represent the positive and negative outputs of the finished mobile phone battery (see the right side of the picture).

　　4. Protection parameters of lithium-ion protection circuits

　　In addition, complex and advanced lithium-ion batteries (such as smart lithium-ion batteries) will also include temperature protection, fuel metering, real-time clock and electronic range identification code.

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