Lithium battery has many applications in reality, and there are many lithium batteries in many electronic devices. In previous articles, the small series of lithium battery protection board failure has been described. In order to enhance our understanding of lithium battery, this paper will introduce the use of lithium battery protection board, as well as the purchase points of lithium battery protection board. If you are interested in lithium battery or lithium battery protection board, you may as well read on.
1、 How to use lithium battery protection board
The circuit and parameters of lithium battery protection board are different according to the IC and voltage. The following is explained by dw01 with MOS tube 8205a
1. The normal working process of lithium battery protection board is: when the cell voltage is between 2.5V and 4.3v, the first and third pins of dw01 output high level (equal to the supply voltage), and the second pin voltage is 0V. At this time, the voltages of the first and third pins of dw01 will be added to the fifth and fourth pins of 8205a respectively. Because the G pole of the two electronic switches in 8205a receives the voltage from dw01, they are in the on state, that is, the two electronic switches are in the on state. At this time, the negative pole of the cell is directly connected with the p-terminal of the protection board, and the protection board has voltage output.
2. Over discharge protection and control principle of protection board: when the cell discharges through the external load, the voltage of the cell will slowly decrease. At the same time, dw01 will monitor the cell voltage in real time through R1 resistance. When the cell voltage drops to about 2.3V, dw01 will consider that the cell voltage has been in the over discharge voltage state, and immediately disconnect the output voltage of the first pin, so that the voltage of the first pin becomes 0V, within 8205a The switch tube of is closed because there is no voltage at the fifth pin.
At this time, the B – of the cell is disconnected from the p – of the protection board. That is, if the discharge circuit of the cell is cut off, the cell will stop discharging. The protection board is in the over discharge state and is always in the over discharge state. When the P and P – of the protection board are indirectly charged, dw01 stops the over discharge state immediately after the B – detects the charging voltage, and outputs a high voltage at the first pin again to turn on the over discharge control tube in 8205a, that is, the B – of the cell and the p – of the protection board are connected again, and the cell is charged directly by the charger.
3. Overcharge protection and control principle of lithium battery protection board: when the battery is charged normally through the charger, with the increase of charging time, the cell voltage will be higher and higher. When the cell voltage rises to 4.4V, dw01 will consider that the cell voltage is in the overcharge voltage state, and immediately disconnect the output voltage of the third pin, so that the voltage of the third pin becomes 0V, The switch tube in 8205a is closed due to no voltage at pin 4. At this time, the B – of the cell is disconnected from the p – of the protection board. That is, if the charging circuit of the cell is cut off, the cell will stop charging.
The protection board is in the overcharge state and remains unchanged. After the P and P – of the protection board indirectly discharge the load, although the overcharge control switch is closed, the positive direction of the diode inside is the same as that of the discharge circuit, so the discharge circuit can discharge. When the voltage of the cell is lower than 4.3v, dw01 stops the overcharge protection state, and outputs high voltage at the third pin again, making the overcharge control tube in 8205a conduct That is, the B – of the cell and the p – of the protection board are connected again, and the cell can charge and discharge normally.
4. Control process of short circuit protection: short circuit protection is a limiting form of over-current protection, and its control process and principle are the same as over-current protection. Short circuit is equivalent to adding a small resistance (about 0 Ω) between PP -, so that the load current of the protection board can reach more than 10A instantaneously, and the protection board will carry out over-current protection immediately.
The function of lithium battery protection board is to prevent overcharge or overdischarge of lithium battery. The battery itself can be well protected if there is a protection board. If there is no protection board, the lithium battery itself is easy to be damaged, and there are safety risks. This is not a joke. Of course, if you don’t use the protective board, because the internal resistance is small, it may last a little longer and the price is cheaper. But I think safety is the first.
2、 Key points of purchasing lithium battery protection board
In order to protect the life of lithium battery pack, it is recommended that the battery charging voltage should not exceed 3.6V at any time, that is, the protection voltage of lithium battery protection board should not be higher than 3.6V, the equalization voltage should be 3.4v-3.5v, and the battery discharge protection voltage should generally be higher than 2.5V.
The maximum voltage of the charger is recommended to be 3.5 strings. The larger the self discharge is, the longer the equalization time will be. It is difficult to balance the cells with too large self discharge and need to be eliminated. So when choosing the lithium battery protection board, try to choose 3.6V overvoltage protection, 3.5V start balanced.
In a word, the lower the internal resistance of the lithium battery protection board, the better, and the lower it is, the less it will generate heat. The current limiting capacity of the protection board is determined by the sampling resistance of copper wire, but the continuous current capacity is determined by MOS.