The protection measure and working theory of Lithium ion battery

1. Polymeric Positive Temperature Coefficient （PTC）

PTC is shorten for Polymeric Positive Temperature Coefficient, PTC is macromolecule polymer positive temperature coefficient, if this parts have protection for the circuit when the current surge is too large and temperature is too high. And when in use, concatenation it in the circuit, under normal circumstances, its resistance is very small, also wastage is very small, which  did not affect the normal work of the circuit, but if the happens the overcurrent(like short circuit), its temperature rise. And its resistance sharply higher accordingly , which has the function of limits the current. to avoid damage to the components in the circuit, after the trouble is eliminate. The temperature of PTC will be down automatically, and Back to the low resistance state, so PTC part is also called recoverability fuse.

 In the manufacturing of lithium battery, PTC placed inside the battery, and in series with Battery charge and discharge circuit, mainly prevent batteries happens external short-circuit fault in the absence of other protective measures.

2. PCM

The lithium battery itself has instability, if happens the overcharge(overvoltage) or current overload(overcurrent), then it will has the burn or explosion, if happens the overdischarge, then will has the irreversible damage, so the battery must have the PCM assist. Which will minimize the lithium ion battery of the potential risk of reduced.

The lithium battery PCM is the protection electronic circuit for the single cell or the battery pack, the PCM has the function of overcharge protection, overdischarge protection, and overcurrent protection.

The basically structure and theory of PCM : One protect IC. It is precisely obtain the reliable protection parameter, other one is MOSFET, it is mainly  acts as a high-speed switch in the discharge circuit, execute the protection action, IC can IC by monitoring the battery voltage difference to control the MOS tube, common PCM still have the resistance, capacitance, and supplementary FUSE、PTC、NTC、ID and storage etc, the B+、B-, respectively connected battery cell positive and negative, and P+、P- respectively connected positive and negative of PCM output. When the voltage of battery higher or lower than a certain value( a critical value of battery overcharge or overdischarge), Output signal by cutting off the MOS tube disconnect circuit, so as to realize the overcharge and overdischarge protection for the lithium battery.

MOS tube has a certain resistance, the voltage of MOS tube will change follow by circuital current, and when its voltage greater than setting value( the current too larger), the output signal of IC control the MOS tube cutting off the circuit, To reach the role of over-current protection

With PCM battery packs, when it is full charge, it can assure the voltage difference of each single cell less then setting value( usually ±20mV). Which Implementation equalized Charging of each singe cell. And effectively improve charge effect under the in series charge ways, also in the meantime detective each single cell of the battery pack overcharge, overdischarge, short circuit and overtemperature status. It protect and extend the battery use life.

MOS tube has a certain resistance, the voltage of MOS tube will change follow by circuital current, and when its voltage greater than setting value( the current too larger), the output signal of IC control the MOS tube cutting off the circuit, To reach the role of over-current protection