What are the types of 3.7v lithium battery charging circuit diagram?

3.7v lithium battery charging circuit diagram (1)

1, lithium battery charging:

According to the structural characteristics of the lithium battery, the maximum charge termination voltage should be 4.2V, and it should not be overcharged. Otherwise, the lithium ion of the positive electrode will be taken too much, and the battery will be scrapped. The charging and discharging requirements are relatively high, and a dedicated constant current and constant voltage charger can be used for charging. Normally, the constant current is charged to 4.2V/section and then switched to constant voltage charging, when the constant voltage charging current drops to within 100mA, the charging should be stopped.

Charging current (MA) = 0.1 to 1.5 times

Battery capacity (such as 1350mAh battery, its charging current can be controlled between 135 ~ 2025mA). The normal charging current can be selected to be about 0.5 times the battery capacity, and the charging time is about 2 to 3 hours.

2. Discharge of lithium battery

Due to the internal structure of the lithium battery, lithium ions cannot all move to the positive electrode during discharge, and a part of lithium ions must be reserved at the negative electrode to ensure that lithium ions can be smoothly inserted into the channel during the next charging. Otherwise, the battery life will be shortened accordingly. In order to ensure that some lithium ions remain in the graphite layer after discharge, it is necessary to strictly limit the minimum voltage at the end of discharge, that is, the lithium battery cannot be over-discharged. The discharge termination voltage is usually 3.0V/section and the minimum cannot be lower than 2.5V/section. The length of battery discharge is related to the battery capacity and discharge current. Battery discharge time (hours) = battery capacity / discharge current. Lithium battery discharge current (MA) should not exceed 3 times the battery capacity. (For example, 1000mAH battery, the discharge current should be strictly controlled within 3A) otherwise the battery will be damaged.

3, lithium battery protection circuit

It consists of two FETs and a dedicated protection integrated block S--8232. The overcharge control transistor FET2 and the over discharge control transistor FET1 are connected in series to the circuit. The protection IC monitors the battery voltage and controls it when the battery voltage rises to 4.2V. The overcharge protection tube FET1 is turned off to stop charging. In order to prevent malfunction, a delay capacitor is generally added to the external circuit. When the battery is in the discharged state and the battery voltage drops to 2.55V, the over discharge control transistor FET1 is turned off, and the supply of power to the load is stopped. Over current protection is to control the FET1 to turn off and stop discharging to the load when a large current flows through the load, in order to protect the battery and the FET.

4, charging circuit:

Principle: Use a constant voltage to charge the battery to ensure it does not overcharge. The input DC voltage is higher than the charged battery voltage by 3 volts. R1, Q1, W1 and TL431 form a precision adjustable voltage regulator circuit, Q2, W2 and R2 form an adjustable constant current circuit, and Q3, R3, R4, R5 and LED are charging indicating circuits. As the voltage of the recharged battery rises, the charging current will gradually decrease. After the battery is fully charged, the voltage drop across R4 will decrease, so that Q3 will be turned off and the LED will be extinguished. To ensure that the battery is sufficient, please continue after the indicator is off, and charge for 1-2 hours. Please use the appropriate heat sink for Q2 and Q3 when using.

3.7v lithium battery charging circuit diagram (2)

Input is Mini USB port

The charging voltage cannot exceed 8V. The charging current is 1A and can be charged with the Android phone charger.

The red indicator light is on when charging, and the green indicator light is on when fully charged.

1. Design method:

Main control chip: TP4056

Typical applications on the chip manual:

2. Calculation of RPROG resistance

This resistor determines the maximum charging current

Charging current I=1200/RPROG

Here RPROG is selected to be 1.2k and the maximum charging current is 1A.

3, the choice of resistor R4

The role of R4: increase the thermal regulation current; reducing the voltage drop across the internal MOSFET can significantly reduce the power consumption in the IC. This has the effect of increasing the current delivered to the battery during thermal conditioning. One of the countermeasures is to dissipate a portion of the power through an external component such as a resistor or diode.

The charger will generate heat when it is working. In the case of heat, for example, the maximum charging current is 1A. In fact, after charging, the charging current is less than 1A, and the hotter output current is smaller. To solve this problem, the official gives a countermeasure is to connect a resistor and dissipate part of the power.

Let this resistor take part of the heat and reduce the heat of the chip to increase the charging current of the lithium battery.

Calculation formula:

Here we choose 0.25 ohms, the package is 1206, and the power can reach 0.25W. Assume that the current through the 0.25 ohm resistor is 1A and the power is 0.25W. In fact, the charging current cannot reach 948mA, so the power is less than 0.25W.

3.7v lithium battery charging circuit diagram (3)

The battery is 3.7v720mAh, the charging circuit schematic is as follows, constant current, voltage limiting charging mode.

3.7v lithium battery charging circuit diagram (4)

3.7V lithium battery automatic charging circuit

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