Why can't lithium battery single-cell protection board be used in series with multiple cells?

1: Charging: Assuming that a certain battery reaches 4.2V maintenance voltage first, for example, after maintenance of the cout charging tube on the B maintenance board, the internal resistance is infinite. At this time, the current is disconnected by this tube. Generally, a single-cell lithium battery is on the maintenance board. The withstand voltage of the FET is very low, so it may be broken down (but due to the charging condition, the charging voltage is subtracted from all battery voltages, and generally does not exhibit overvoltage). After other B charging tubes are maintained, the charging voltage will be single Adding to the VDD terminal of the B maintenance board may show overpressure, causing damage to the integrated block of the B maintenance board. 2: Discharge: Assume that a certain battery reaches the 2.7V maintenance voltage first. For example, after the maintenance of the Dout charging tube on the A maintenance board, the internal resistance is infinite. At this time, the current is disconnected by this tube. At this time, it is assumed that there are 6 sections in the circuit. Battery, then this tube will withstand a voltage of up to 25V, the DOUT field effect tube in the green circle in the figure will be soft breakdown, so even if the maintenance action, there will be a few milliamperes, if it is completely damaged, it will be very Strong current passes through, and it loses its maintenance purpose. In addition, after the maintenance of this tube, there will be a back pressure of up to 25V from the V- terminal of the A board to the VSS terminal of the A board, and a back pressure of about 21V from the v- to the VDD terminal, which may completely cause the chip to be damaged. Another point to note in the above picture is that the FET is a dual-guide pass device. Under normal circumstances, even if the driving voltage is not applied, the current can move in the direction of the arrow in the icon. For example, when dout is high in the figure above, the current can be The reverse arrow moves in the reverse direction. When DOUT is low, the current can only move along the arrow, but the activity in the reverse arrow direction is cut off. Therefore DOUT is the discharge control terminal. Under normal circumstances, even if the high potential is not applied, it can move in the direction of the arrow, but there is a voltage drop of about 0.3V inside. Therefore, in order to eliminate the internal voltage drop and add a high level, the internal pressure drop along the arrow direction will almost be A few millivolts-tens of millivolts. Therefore, the FET is a dual-guide through control device. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.