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Cell phone battery repair instrument birth background:
With the needs of the development of contemporary society, almost everyone is using mobile phones, and mobile phones have become a daily necessities that we cannot do. In people's frequent use, it is gradually found that the mobile phone battery can not meet our requirements, and often after a period of use, there is a situation in which the charging time becomes short. A battery that has just been recharged has no power for a long time, so a repair device for repairing the battery of the mobile phone is born.
Design principle
(1) Introduction of mobile phone battery
Nowadays, lithium-ion batteries are used in general mobile phone batteries. Mainly because the lithium ion battery is lithium ion (Li-Ion) and lithium polymer (Li-Pol), the battery has the characteristics of light weight, large capacity and small internal resistance. But we need to charge according to its characteristics, otherwise it will be very damaged, and its recharge number will be greatly discounted.
Lithium ion needs to pay attention to not overcharge and overdischarge during charging. It has its own minimum voltage and maximum voltage. Generally, the lowest voltage is between 2.2V and 2.3V, and the highest voltage is between 4.2V and 4.3V, so we Care must be taken when setting up the circuit to set the discharge termination voltage and charge termination voltage.
(2) Design ideas
The design circuit is mainly divided into two stages of discharge and charging. A typical charger simply charges the battery, and the repairer has an additional discharge process.
The discharge phase is mainly to completely discharge the residual power in the battery and bring its voltage to the discharge termination value. The discharge phase mainly pays attention to the setting of the discharge voltage termination value. If the battery is over-discharged, it will cause great damage to the battery.
In the charging phase, we are different from the general charger, which uses a pulse signal whose frequency changes periodically to charge the battery. The main consideration is that the pulse signal can gradually activate the chemicals in the battery to make the battery reach the factory. Similarly, the charging voltage termination value cannot be exceeded during charging, and overcharging may cause permanent damage to the battery.
Production process
(1) Design of the discharge circuit
1. Design requirements
1 discharge current can generally take 0.2 times the rated capacity of the battery.
2 The discharge termination voltage must be accurately understood to avoid damage to the battery due to overdischarge.
3 Start and stop the discharge in manual mode.
2, design points
1 When the battery is discharged to the termination voltage, the discharge circuit should be automatically disconnected or automatically transferred to the charging state.
2 It is convenient to monitor the discharge working state.
The following is a schematic diagram of the discharge circuit design:
Discharge circuit diagram
The drive circuit part can be composed of two relays to form a self-locking circuit. When the discharge is finished, the switch is automatically disconnected and transferred to the charging part.
(two) the design of the charging circuit
1. Design indicators
1 adjustable constant current charging, maximum charging current 500mA.
2 At the end of the discharge, it automatically switches to the constant current charging state.
3 When charging to the charge termination voltage, the constant current circuit stops working and locks the "charge end" state.
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