The lithium battery protection board is the charge and discharge protection of the series lithium battery pack; when fully charged, it can ensure that the voltage difference between the individual cells is less than the set value (generally ±20mV), and realize the equal charge of the individual cells of the battery pack , Which effectively improves the charging effect in the series charging mode; at the same time, it detects the overvoltage, undervoltage, overcurrent, short circuit, and overtemperature status of each single battery in the battery pack to protect and extend the battery life; undervoltage protection makes every A single-cell battery is used to avoid damage to the battery due to over-discharge.

1. Software protection board lithium battery has no display, low output voltage, no load:
For such defects, first rule out the bad battery (the battery has no voltage or the voltage is low). If the battery is bad, the self-consumption of the protection board should be tested to see if the self-consumption of the protection board is too large and the battery voltage is low. If the cell voltage is normal, it is because the entire circuit of the protection board is blocked (components are soldered, false soldered, FUSE is poor, PCB internal circuit is blocked, vias are blocked, MOS, IC is damaged, etc.). The specific analysis steps are as follows:

(1) Connect the black test lead of a multimeter to the negative pole of the battery cell, and connect the red test lead to the FUSE, R1 resistor terminals, the Vdd, Dout, and Cout terminals of the IC, and the P+ terminal (assuming the battery cell voltage is 3.8V). These test points should all be 3.8V. If not, there is a problem with this circuit.
1. There is a change in the voltage across FUSE: test whether the FUSE is turned on, if it is turned on, the internal circuit of the PCB board is not turned on; if it is not turned on, there is a problem with the FUSE (bad incoming material, overcurrent damage (MOS or IC control failure), There is a problem with the material (the FUSE is burned out before the MOS or IC is activated), then use a wire to short the FUSE, and continue to analyze later.
2. There is a change in the voltage across the R1 resistor: test the resistance value of R1. If the resistance value is abnormal, it may be a virtual weld and the resistor itself is broken. If the resistance value is not abnormal, there may be a problem with the internal resistance of the IC.
3. The voltage of the IC test terminal changes: the Vdd terminal is connected to the R1 resistor. Dout, Cout end abnormal, it is due to the IC weak welding or damage.
4. If there is no change in the previous voltage and the voltage between test B- and P+ is abnormal, it is because the positive via of the protection plate is blocked.

(2) Connect the red test lead of the multimeter to the positive electrode of the battery. After activating the MOS tube, the black test lead is connected to the MOS tube 2, 3, 6, 7 and P- terminal in turn.
1. If the voltage of MOS tube 2, 3, 6 and 7 has changed, it means MOS tube is abnormal.
2. If there is no change in the voltage of the MOS tube and the voltage at the P- terminal is abnormal, it is because the negative via of the protection plate is blocked.

2. Software protection board lithium battery short circuit without protection:
1. There is a problem with the VM terminal resistance: use a multimeter to connect one test pen to IC2 pin, and one test pen to the MOS pin connected to the VM terminal resistor to confirm the resistance value. Check the resistance and IC, MOS pin for false soldering.
2. IC and MOS abnormality: Since the over-discharge protection and over-current and short-circuit protection share a MOS tube, if the short-circuit abnormality is due to MOS problems, the board should not have over-discharge protection.
3. The above are defects under normal conditions, and short-circuit abnormalities caused by poor IC and MOS configurations may also occur. For example, in the BK-901 that appeared in the previous period, the delay time in the IC with the model number ‘312D’ was too long, which caused the MOS or other components to be damaged before the IC took the corresponding action control. Note: The easiest and direct way to determine whether the IC or MOS is abnormal is to replace the suspected components.

3. Software protection board lithium battery short circuit protection without self-recovery:
1. The IC used in the design has no self-recovery function, such as G2J, G2Z, etc.
2. The short-circuit recovery time of the instrument is too short, or the load is not removed during the short-circuit test. For example, the test leads are not removed from the test end after the short-circuit test leads are short-circuited with the multimeter voltage file (the multimeter is equivalent to a load of several megabytes).
3. Leakage between P+ and P-, such as impurity rosin between the pads, impurity yellow glue or P+, P- capacitance breakdown, IC Vdd to Vss breakdown. (The resistance is only a few K to several hundred K).
4. If none of the above is a problem, the IC may be broken down. You can test the resistance between the pins of the IC.

4. the internal resistance of the software protection board lithium battery is large:
1. Since the internal resistance of MOS is relatively stable and the internal resistance is large, the first thing to suspect should be the components that are relatively easy to change such as FUSE or PTC.
2. If the resistance of FUSE or PTC is normal, check the resistance of the via hole between the P+ and P- pads and the component surface depending on the structure of the protection board. The via may be micro-disconnected and the resistance is relatively large.
3. If there are no problems with the above, it is necessary to doubt whether the MOS is abnormal: first determine whether there is a problem with the welding; secondly, the thickness of the billboard (whether it is easy to bend), because the bending may cause abnormal pin welding; then the MOS tube Put it under a microscope to observe whether it is broken; finally use a multimeter to test the resistance of the MOS pin to see if it is broken down.

5. The software protection board lithium battery ID is abnormal:
1. The ID resistance itself is abnormal due to virtual welding, breakage or failure of the resistance material: both ends of the resistance can be re-welded. If the ID is normal after re-welding, the resistance is virtual welding. If it is broken, the resistance will be split after re-welding. open.
2. ID via is not conducting: use a multimeter to test both ends of the via.
3. There is a problem with the internal circuit: you can scrape the solder mask to see if the internal circuit is disconnected or short-circuited.