Charging and using button lithium manganese battery
2021 Dec 23 By admin 0 comment

1. Practical application of button lithium manganese battery
Button-type lithium manganese batteries are commonly used. For example, CR2032 lithium manganese batteries are often used on computer motherboards to supply power to CMOS circuits. CR2025 lithium manganese batteries are often used in electronic dictionaries. CR2016 and SR44, SR626 and other lithium manganese batteries are often used in calculators.

In addition, because the single-cell button-type lithium manganese battery has a rated voltage as high as 3V, it is very suitable for integrated circuit power supply. Therefore, button-type lithium manganese batteries are commonly used in access control cards of some hotels, in instruments and meters, and in electronic products such as MP3, MP4, and model airplanes.

2. Safe charging method of button type lithium manganese battery
The button-type lithium manganese battery can be charged with a safe charger as shown in Figure 1. It can charge the lithium-manganese battery G in an approximate constant current mode when the power of the lithium manganese battery G is insufficient. When the battery voltage reaches 3.5V, it can automatically switch to constant voltage charging to ensure that the battery voltage is stable at 3.5V, thereby ensuring the safety of charging. The principle is as follows.

Charging and using button lithium manganese battery
Figure 1 Button type lithium manganese battery safety charger

The AC power connected by the plug XP is stepped down by the transformer T, rectified by the diodes VD1~VD4, and filtered by the capacitor C1, and then DC power is obtained at both ends of C1.

When the charger is loaded into the lithium manganese battery G with a voltage lower than 3V, the battery voltage is divided by R4 and RP and added to the REF terminal of the TL431 precision voltage regulator integrated circuit IC, because the voltage division value at this time is lower than the internal TL431 The 2.5V reference voltage makes the IC cut off, the transistor VT is turned on by the resistor R2 and the light-emitting diode LED, and the DC power supply is charged to G with a current of about 200mA through the resistors R1 and VT.

When the battery is charged to 3.5V, the divided voltage applied to the REF terminal of the IC will reach 2.5V, so the K and A terminals of the control IC are turned on and set to a regulated state of 2.5V. The base is clamped at 2.5V. At this time, the VT launch junction is cut off due to the reverse bias and stops charging G.

After testing, the IC’s state can be reversed as long as the REF terminal voltage of the IC changes 3mV up and down the reference voltage. Therefore, the error of the control battery charging to 3.5V termination voltage will not exceed ±6mV, which can ensure the protection of lithium manganese The battery is safely charged.

In the circuit, the red light-emitting diode LED1 is used for charging instructions, and the green light-emitting diode LED2 is used for power-on instructions.

The charger needs debugging. The debugging method is: first do not connect to battery G, but use 5.1kΩ resistor, 1000μF capacitor and digital voltmeter in parallel to replace G, and then adjust RP so that VT is just right when the voltage across the resistor reaches 3.5V The deadline is fine.

The charger can also be used for constant voltage charging of lithium-ion batteries after adjusting the RP, which is very safe and practical.

3. Inspection and repair of electrical failure caused by undervoltage of button-type lithium manganese battery
There is a CMOS unit circuit in the desktop computer, which is used to store the computer’s hardware configuration parameters, date and time and other information. It needs power supply for many years to ensure that the information is not lost. When the computer is powered on, the internal power supply provides the operating voltage to the CMOS circuit; when the computer shuts down, it is powered by the internal battery. Many computers use a 3V button-type lithium manganese battery for power supply.

The above shows that the button-type lithium manganese battery used in the computer must maintain sufficient voltage for a long time to reliably supply power to the CMOS circuit after shutdown. At the same time, it is shown that the button-type lithium manganese battery is in a charging state or a floating charging state for a long time when the computer is turned on.

There is an ASTP286 computer. After setting the time, turn off the power of the main computer and turn it on again after ten minutes. It is found that the clock has stopped, but other configurations have not changed. According to the above-mentioned principle analysis, this kind of failure of the computer is likely to be caused by the lack of battery voltage and the loss of information. Open the case and use a multimeter to measure the battery voltage with the DC voltage block, and it is only 1.6V, which shows that the analysis is correct. When I switched on a button-type lithium manganese battery of the same specification, the clock returned to normal. It means that the original button-type lithium manganese battery has been used for too long and should be replaced when it reaches the end of its service life.