Lithium-ion battery protection board current selection
1. The lithium-ion battery protection board current is determined by the detection voltage of the protection IC and the internal resistance of the MOS tube. If the protection IC cannot be changed, you can change the MOS tube, such as DW01 and 8205MOS, using a MOS tube is 2 ~ 5A, using two The MOS tube parallel current will double. At present, some large-capacity mobile power supplies use 3 to 4 MOS tubes in parallel.
2. Protection board protection current = overcurrent detection voltage / MOS tube internal resistance (Because two MOS tubes are connected in series, the MOS tube internal resistance must be multiplied by 2)
3. Lithium-ion battery protection board selection depends on the battery capacity. Generally, there are no special requirements for batteries below 2000mAh. Select a general protection board. The protection current is 2 ~ 5A. The discharge current of general batteries is 1C. Battery protection current above 2000mAh is better than 3A. Regarding power lithium batteries, many have not added a protection board, but PTC is connected in series. When the temperature is too high, the power is automatically cut off.
How to use the lithium ion battery protection circuit board？
Lithium-ion battery protection board has different circuits and parameters according to different ICs, voltages, etc. The following uses DW01 with MOS tube 8205A to explain:
1. The normal working process of the lithium-ion battery protection board is: when the battery voltage is between 2.5V and 4.3V, both pins 1 and 3 of DW01 output high level (equal to the supply voltage), and the second pin The voltage is 0V. At this time, the voltage of pin 1 and pin 3 of DW01 will be added to pins 5 and 4 of 8205A. The two electronic switches in 8205A are in the on state because their G poles are connected to the voltage from DW01. Both electronic switches are on. At this time, the negative electrode of the battery core is directly connected to the p-terminal of the protective plate, and the protective plate has a voltage output.
2. Protection board over-discharge protection control principle: When the battery core is discharged through an external load, the voltage of the battery core will slowly decrease. At the same time, DW01 will monitor the battery voltage in real time through the R1 resistor. At 2.3V, DW01 will think that the cell voltage is already in the over-discharge voltage state, and immediately disconnect the output voltage of pin 1 to make the voltage of pin 1 become 0V. The switch in 8205A is turned off because there is no voltage at pin 5.
At this time, the B- of the battery cell and the p- of the protective plate are in an off state. That is, the discharge circuit of the battery cell is cut off, and the battery cell will stop discharging. The protection board is in an over-discharged state and remains on. After p and p- of the protection board are indirectly charged, DW01 stops the over-discharge state immediately after B- detects the charging voltage, and outputs a high voltage on pin 1 again to make the over-discharge control tube in 8205A conductive. That is, B- of the battery cell and p- of the protection board are connected again, and the battery cell is directly charged by the charger.
3. Lithium-ion battery protection board overcharge protection control principle: When the battery is normally charged through the charger, with the increase of the charging time, the voltage of the battery cell will become higher and higher, and when the battery cell voltage rises to 4.4V DW01 will think that the cell voltage is already in the overcharge voltage state, and immediately disconnect the output voltage of pin 3, so that the voltage of pin 3 becomes 0V, and the switch in 8205A is turned off because there is no voltage on pin 4. At this time, the B- of the battery cell and the p- of the protective plate are in an off state. That is, the battery's charging circuit is cut off, and the battery will stop charging.
The protection board is in an overcharged state and remains on. After the p and p- of the protection board are indirectly discharged, the overcharge control switch is turned off, but the positive direction of the internal diode is the same as the direction of the discharge circuit, so the discharge circuit can discharge. When the voltage of the battery cell When it is lower than 4.3V, DW01 stops the overcharge protection state and outputs a high voltage on pin 3 again, so that the overcharge control tube in 8205A is turned on, that is, the battery B- and the protection board p- are connected again. , The battery can perform normal charge and discharge.
4. Short-circuit protection control process: Short-circuit protection is a limit form of over-current protection. Its control process and principle are the same as over-current protection. A short-circuit is only equivalent to adding a small resistance value (about 0Ω) Make the load current of the protection board reach above 10A instantaneously, and the protection board immediately performs overcurrent protection.
Lithium-ion battery protection board, its role is to prevent the lithium-ion battery from being overcharged or overcharged and play a corresponding protective role. A protective plate can protect the battery itself. If not, first, the lithium-ion battery itself is easily damaged, and second, there is safety danger. This is not a joke. Of course, the protection board is not used, because the internal resistance is small, the use time may be a little longer, and the price is cheaper, but personally, it is still safety first.
Lithium-ion battery protection circuit board purchase points
In order to protect the life of the lithium-ion battery pack, it is recommended that the battery charge voltage not exceed 3.6V at any time, that is, the protection voltage of the lithium-ion battery protection board is not higher than 3.6V, the equilibrium voltage is recommended to be 3.4V-3.5V, and the battery discharge protection voltage is generally 2.5V That's it.
The charger recommends a maximum voltage of 3.5 strings. The larger the self-discharge, the longer the equalization time. The cells with excessive self-discharge are already difficult to equalize and need to be eliminated. Therefore, when choosing a lithium-ion battery protection board, try to choose 3.6V overvoltage protection, start around 3.5V balanced.
In short, the lower the internal resistance of the lithium-ion battery protection board, the better, and the lower the heat generation. The current limit of the protection board is determined by the constantan wire sampling resistance, but the continuous current capability is determined by MOS.
