This article comes from the network, the author is unknown. This article mainly introduces the protection circuit of cell phone battery. All of us in the use of batteries will always occur when all kinds of misoperation, and cell phone battery is actually relatively fragile batteries, so complete protection measures for a qualified mobile phone battery is essential. The following is the text:
I. The protection of NI-MH battery
Cell Phone Ni-MH battery protection device is very simple, which is in the diagram of the two power-saving core between the flat flat of the same thing, called a recoverable fuse, also known as PTC, that is, the temperature coefficient thermistor in English shorthand. On the circuit, it is in series in the power supply circuit. Once a large current (such as a short circuit), the PTC effect will rapidly increase its own resistance value, play a role in the circuit breaker. Second, the introduction of PTC
PTC Positive temperature coefficient thermistor, also known as polyswitch polymer self-recovery fuse (polymer resettable fuse). The polymer self-recovery fuse consists of a polymer matrix and a carbon black particle that makes it conductive. Since the polymer fuses as a conductor, the current is passed through. When there is a current through the polymer self-recovery fuse, the resulting heat (for I2R) will make it swell. Thus the carbon black particles will be separated and the resistance of the polymer self recovery fuse will rise. This will make the polymer self-recovery fuse faster to produce heat, expand more, and further increase the resistance. When the temperature reaches 125°c, the resistance changes significantly, so that the current decreases significantly. At this point the small current flowing through the polymer self-recovery fuse is sufficient to keep it at this temperature and in a high resistance state. When the fault is cleared, the polymer fuses to the original shape, and the carbon black particles are connected again, thereby reducing the resistance to the level of the specified maintaining current. The above procedure can be cycled several times. The principle of PTC protection is as follows:
The cold State PTC Resistance value is only dozens of msv, while the thermal resistance value is up to kilometers ohms. Third, lithium-ion battery protection line
This article is mainly illustrated with illustrations.
Figure left is a typical lithium-ion protection circuit schematic, B + and B-represent the typical positive and negative poles, while p+ and p represent the positive and negative output of the finished cell phone battery (see figure right). Iv. protection parameters of lithium-ion protection line
In addition, sophisticated lithium-ion batteries (such as smart lithium-ion batteries) also contain temperature protection, metering, real-time clocks and electronic range identification codes. Five, Lithium ion battery protection principle fine solution
1, overcharge protection
When the charge voltage exceeds the protection value, trigger the protection line action, turn off the switch tube Q1.
2, over put protection
When the load to reduce the battery voltage below the protection voltage, triggering the protection line, Q1 shut off.
3. Short Circuit protection
Short-circuit protection circuit is divided into two kinds, one is once triggered, short-circuit troubleshooting, Q1 self conduction, another trigger will not restore their own, the need for outside force to release Q1. At present the two kinds of protection circuit coexist in the market. Vi. definition and interpretation of battery other pins
In the battery output of many mobile phones, in addition to positive and negative, there will usually be one or several other output terminals, typically like two types of graphs, NTC resistors and ID resistors.
1, the principle of ID resistance
ID (identification of the spelling)
Simply put, the cell phone by reading the resistance of the pin resistor to learn the type of battery (according to the different resistance to distinguish Ni-MH batteries and lithium-ion batteries, distinguish between large-capacity and ordinary-capacity batteries).
2, NTC resistance
The NTC resistor is just the opposite of the front ptc resistor. The NTC is a simple spell of a negative temperature coefficient thermistor.
Simply speaking, the cell phone gets the temperature value of the battery by reading the resistance. To carry out corresponding protective actions, such as in the environment outside the 0~45度, mobile phones do not charge, outside the range of-20~60度 mobile phones forcibly shut down, in order to protect in the non-battery tolerance environment dangerous operation.
3. Principle of NTC
The relation of resistance and temperature of NTC resistor as shown in the figure above, it can be seen that there is a very definite correspondence between the resistance and the temperature. The resistor can also be used to compensate for the negative temperature of some circuits. VII. Integrated Circuits
A typical lithium-ion battery comprehensive protection circuit, from left to right respectively for the electric meter circuit/protection circuit/real-time clock.
One of the benefits of a real-time clock circuit in a battery pack is that even if the battery is unplugged from the phone, the clock is not lost, as long as the battery voltage does not fall below 3.0V. And now most real-time clock circuits are placed in the mobile phone, only a small capacity of the backup battery to power, a little cell phone after the power to maintain a very limited time.