Lithium battery protection board to achieve over-charge protection and recovery protection, over-discharge protection and over-discharge protection recovery control, charging and discharging over-current protection, short-circuit protection, protection delay setting, temperature protection and other functions. National people create a warm reminder that the lithium battery single protection board can not be used in series with multiple Oh, with a single lithium battery protection board to do multi-section series use will have the following problems: 1: charging: assume that a particular lithium battery protection board can be used in series.
1: charging: assume that a battery first reached 4.2V protection voltage, such as B protection board cout charging tube protection action, the internal resistance is infinity, at this time, the current is divided by this tube disconnected, the general single lithium battery protection board field effect tube voltage is very low, so there is a possibility of breakdown (but due to the charging state, the charging voltage minus all battery voltage, there is generally no overvoltage phenomenon), in addition B charging tube protection, charging voltage will be added to the VDD side of the B protection board single, there is a possibility of over-voltage, resulting in B protection board integrated block damage.
2: discharge: assume that a battery first reached 2.7V protection voltage, such as A protection board Dout charging tube protection action, the internal resistance of infinity, at this time, the current is divided by this tube to disconnect, this time, assuming that there are six batteries inside the circuit, then this tube will withstand up to 25V, the green circle on the figure DOUT field effect tube will be soft breakdown, so that, even if the protection action, there will be There are a few milliamps, if completely damaged, there will be a very strong current through, and the loss of protection. In addition, after the protection of this tube A board V- terminal to A board VSS terminal appears up to 25V counter-voltage, v- to VDD terminal will also appear about 21V counter-voltage, it is possible to lead to the destruction of the chip.
In addition, the analysis of the above chart is worth noting that the field effect tube is a dual conductor device, under normal circumstances, even without adding drive voltage, the current can also flow in the direction of the arrow in the icon, such as the above chart dout for high potential, the current can reverse the flow of the arrow, when DOUT for low potential, the current can only flow with the arrow, but the anti-arrow direction flow is cut off. Therefore, DOUT is the discharge control terminal.
Under normal circumstances, even without the high potential, can flow in the direction of the arrow, but the internal voltage drop of about 0.3V, so in order to eliminate the internal voltage drop, plus the high level, then the internal voltage drop in the direction of the arrow will be almost a few millivolts - tens of millivolts. So that the field effect tube is a double-wire controller
