The design and application of mobile phone battery repair instrument

For the needs of modern society, almost everyone is using mobile phones. Mobile phones have become a daily necessities for us. In the frequent use, people gradually find that the mobile phone battery can not meet our requirements for use. Often after a period of use, the battery does not charge or discharge, and the discharge time becomes shorter. This article describes a repair device for repairing mobile phone batteries. By introducing the design principles and design ideas of the product, we will give you a detailed understanding of the product's functions and applications.

For the needs of modern society, almost everyone is using mobile phones. Mobile phones have become a daily necessities for us. In the frequent use, people gradually find that the mobile phone battery can not meet our requirements for use. Often after a period of use, the battery does not charge or discharge, and the discharge time becomes shorter. A newly charged battery will not be used for a long time, and a repair device for repairing a mobile phone battery is born.

Design principle

(a) Introduction to mobile phone batteries

Lithium-ion batteries are commonly used in mobile phone batteries. The main reason is that lithium-ion batteries are lithium-ion (Li-Ion) and lithium-polymer (Li-Pol) batteries, which are characterized by light weight, large capacity, and low internal resistance. But we need to charge it according to its characteristics, otherwise it will be very damaging and its chargeable times will be greatly discounted.

Lithium ions need to pay attention in the charging process can not be overcharged and over-discharge, it has its own minimum voltage and maximum voltage, generally the lowest voltage between 2.2V to 2.3V, the highest voltage between 4.2V to 4.3V, so we When designing the circuit, it is necessary to pay attention to setting the discharge termination voltage and the charge termination voltage.

(two) design ideas

The design circuit is mainly divided into two stages of discharge and charge. A typical charger simply charges the battery, and the repair device has a more discharging process.

The discharge stage is mainly to completely discharge the residual electricity in the battery, and make the voltage reach the discharge termination value. The discharge stage 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 stage, we are different from the general chargers in that we use the pulse signal whose frequency changes periodically to charge the battery. The main consideration is that the pulse signal can gradually activate the chemical substances in the battery, so that the battery reaches the factory effect. Similarly, the charging voltage must not exceed the end of the charging voltage. Overcharging can also cause permanent damage to the battery.

Production process

(a) Design of discharge circuit

1, design requirements

1 discharge current can generally take 0.2 times the rated capacity of the battery.

2 It is necessary to accurately grasp the discharge termination voltage so as not to damage the battery due to over-discharge.

3 Start and stop the discharge manually.

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 charge state.

2 It is convenient to monitor the discharge working status.

The drive circuit part can be composed of two relays to form a self-locking circuit. At the end of discharging, the switch is automatically disconnected and transferred to the charging section.

(B) 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 goes into the constant current charging state.

3 When charging to the charge termination voltage, the constant current circuit stops working and the "charge end" state is locked.

2, design points

1 Use a voltage comparator to monitor the battery voltage to ensure that the charge current is turned off and the “end of charge” state is locked when the charge termination voltage is guaranteed.

2 Automatic function and manual start and stop functions.

The charging circuit combines with the pulse signal to charge the circuit. The pulse signal here can be realized with the 555 timer, and three 555s are used to form a pulse signal whose frequency changes periodically. The connection of the entire circuit needs to have a logical relationship, which can be achieved with a NAND gate. In the design, we use a 4012 four-phase input NAND gate.

(III) Design logic

1, the logic of the discharge circuit

The potential at point A is at a low potential in the discharge state and is high at the charge state. This point potential we recorded for the time being.

2, the charging circuit logic relationship

It can be seen that the potential at point B is at a low potential in the discharged state and is high at the charged state, which is the same as the potential at point A. From this we will connect these two potentials to the input of the NAND gate.

Overall logic

Both points A and B and the pulse signal are connected to the input of the NAND gate, and then a non-gate output signal. In this way, a logical relationship can be formed. As shown in Table 1. Connected to both ends of the battery, here you can use a switch TWH8778 to connect.

The other circuit part, mainly has the power control part, may use the rectification, the filter, the steady voltage will convert the alternating current signal to the direct current power source that we need. Charging current can be charged with a constant current source.

The circuits and devices used in this design are common circuits for us. They are very helpful for current electrical engineering students. Through this kind of electronic production, we can consolidate our professional knowledge, enhance the understanding of various circuits, and the performance of various devices. Instructions.

The repair device for lithium ion batteries is indispensable in the future development. Because of the environmental protection and energy saving features of lithium ion batteries, it will be the focus of future development. Many household electrical appliances will gradually adopt lithium ion batteries.

In addition, the charger can also be modified to charge nickel-cadmium batteries or nickel-metal hydride batteries, its function can be further expanded, leaving a lot of room for thinking.