How to use lithium battery protection board and purchase points
Lithium batteries have many applications in reality, and lithium batteries are present in many electronic devices. This article will introduce the use of lithium battery protection board and the key points of purchasing lithium battery protection board.
How to use lithium battery protection board
The circuit and parameters of the lithium battery protection board are different according to the use of IC, voltage, etc. The following is an explanation with DW01 with MOS tube 8205A:
1. The normal working process of lithium battery protection board
When the cell voltage is between 2.5V and 4.3V, the first pin and the third pin of DW01 both output high level (equal to the supply voltage), and the second pin voltage is 0V. At this time, the voltage of pin 1 and pin 3 of DW01 will be applied to pins 5 and 4 of 8205A respectively. The two electronic switches in 8205A are in the conducting state because their G poles are connected to the voltage from DW01, that is Both electronic switches are in the open state. At this time, the negative pole of the battery is directly connected to the P- terminal of the protection board, and the protection board has a voltage output.
2. Protection board over-discharge protection control principle
When the cell is discharged through an external load, the cell voltage will slowly decrease, and the DW01 will monitor the cell voltage in real time through the R1 resistor. When the cell voltage drops to about 2.3V, DW01 will consider that the cell voltage has been In the over-discharge voltage state, immediately disconnect the output voltage of the first pin, so that the voltage of the first pin becomes 0V, and the switch tube in the 8205A is closed because there is no voltage on the fifth pin.
At this time, the B- of the battery cell and the P- of the protection board are in a disconnected 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-discharge state and has been maintained. After the P and P- of the protection board have indirect charging voltages, DW01 will immediately stop the over-discharge state after B- detects the charging voltage, and output a high voltage at pin 1 again to turn on the over-discharge control tube in the 8205A. That is, the B- of the battery cell and the P- of the protection board are reconnected, and the battery is directly charged by the charger.
3. Lithium battery protection board overcharge protection control principle
When the battery is normally charged by the charger, as the charging time increases, the voltage of the cell will become higher and higher. When the cell voltage rises to 4.4V, DW01 will consider the cell voltage to be in an overcharge voltage state. It immediately disconnects the output voltage of the third pin, so that the voltage of the third pin becomes 0V, and the switch tube in the 8205A is closed because the fourth pin has no voltage. At this time, the B- of the battery cell and the P- of the protection board are in a disconnected state. That is, the charging circuit of the battery cell is cut off, and the battery cell will stop charging.
The protection board is in an overcharged state and has been maintained. After the P and P- of the protection board discharge the load indirectly, although the overcharge control switch is turned off, the forward direction of the diode inside is the same as the direction of the discharge circuit, so the discharge circuit can discharge. When the voltage of the battery cell When the voltage is lower than 4.3V, DW01 stops the overcharge protection state and outputs high voltage on pin 3 again, so that the overcharge control tube in 8205A is turned on, that is, the B- of the battery and the protection board P- are reconnected , The battery cell can be charged and discharged normally.
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. Short-circuit is only equivalent to adding a small resistance (about 0Ω) between PP- to protect the load of the board. When the current reaches more than 10A instantaneously, the protection board immediately performs over-current protection.
Lithium battery protection board, its role is to prevent the lithium battery from being overcharged or over-discharged and play a corresponding protective role. There is a protection board to protect the battery itself. If not, the lithium battery itself is easily damaged, and the other is a safety hazard. This is no 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 I personally think that safety is the first thing.
Points for purchasing lithium battery protection board
In order to protect the life of the lithium battery pack, it is recommended that the battery charging voltage does not exceed 3.6v at any time, that is, the protection voltage of the lithium battery protection board is not higher than 3.6v, the balanced voltage is recommended 3.4v-3.5v, and the battery discharge protection voltage is generally above 2.5v. Can.
The recommended maximum voltage of the charger is 3.5 strings. The greater the self-discharge, the longer the balance will take. The cells with excessive self-discharge are difficult to balance and need to be eliminated. So when choosing a lithium battery protection board, try to choose 3.6v overvoltage protection, about 3.5v to start the balance.
In short, the lower the internal resistance of the lithium battery protection board, the better, and the lower it is, the less heating it is. The current limit of the protection board is determined by the constantan wire sampling resistance, but the continuous current capability is determined by the mos.