Principle knowledge of lithium battery protection board

Lithium battery protection board principle is very simple. There are few electronic components suitable for beginners. The following is the first chapter of the protection board composition and main role mainly introduces the composition of lithium battery protection board, the main role of battery protection board, work principle. And the application range of the single-cell lithium battery protection circuit, electrical performance parameters, main materials, size specifications, and other related items. All project standards described in this specification can be used as quality inspection standards and basis. Product application range: (1) liquid lithium ion rechargeable battery; (2) polymer lithium ion rechargeable battery. First, the composition of the protective plate Lithium battery (chargeable type) needs to be protected. It is determined by its own characteristics. Because the material of the lithium battery itself cannot be overcharged, over-discharged, over-current, short-circuited and ultra-high temperature charge and discharge, the lithium battery lithium battery assembly will always follow an exquisite protection board and a current fuse. The protection function of the lithium battery is usually completed by the protection circuit board and the PT. The protection board is composed of electronic circuits. It can accurately monitor the voltage of the battery and the current of the charging and discharging circuit in the environment of -40 ° C to +85 ° C. Control the on and off of the current loop; PTC prevents the battery from being damaged in a high temperature environment.

The protection board usually includes a control IC, a MOS switch, a resistor, a capacitor, and an auxiliary device NTC, an ID memory, and the like. The control IC controls the MOS switch to conduct under all normal conditions, so that the cell communicates with the external circuit, and when the cell voltage or the loop current exceeds the specified value, it immediately controls the MOS switch to turn off (tens of milliseconds). Protect the safety of the battery cells. NTC is the abbreviation of Negative temperature coefficient, which means the negative temperature coefficient. When the ambient temperature rises, its resistance value decreases. It uses electric equipment or charging equipment to react in time to control internal interruption and stop charging and discharging. The ID memory is often a single-line interface memory, and the ID is the abbreviation of Identification, that is, the meaning of identification, and stores information such as the type of battery and the date of manufacture. Can be used to trace the product and limit the application.

The main role of the protection board is generally required to control the cell voltage and the working current and voltage of the charge and discharge circuit at -25 ° C ~ 85 ° C, under normal conditions, the C-MOS switch tube is turned on, so that The battery cell and the protection circuit board are in normal working state, and when the cell voltage or the operating current in the circuit exceeds the pre-set value of the comparison circuit in the control IC, within 15 to 30 ms (different control ICs have different responses to C-MOS) Time), turn off the CMOS, that is, turn off the battery discharge or charging circuit to ensure the safety of the user and the battery. Chapter 2 Working Principle of Protection Board The working principle of the protection board: As shown in the figure, the IC is powered by the battery, and the voltage can guarantee reliable operation at 2v-5v. 1. Overcharge protection and overcharge protection recovery When the battery is charged so that the voltage exceeds the set value VC (4.25-4.35V, the specific overcharge protection voltage depends on the IC), VD1 flips to make Cout low, T1 cutoff charging stops. When the battery voltage falls back to the VCR (3.8-4.1V, the specific overcharge protection recovery voltage depends on the IC), Cout becomes high level, T1 conduction is continued, and the VCR must be less than a fixed value of VC. Prevent frequent jumps. 2. Over-discharge protection and over-discharge protection recovery When the battery voltage drops to the set value VD (2.3-2.5V, the specific over-charge protection voltage depends on the IC) due to discharge, VD2 flips, after a short time delay, Dout goes low, T2 is turned off, and the discharge stops. When the battery is placed in charge, the internal OR gate is turned over and T2 is turned on again to prepare for the next discharge. 3. Over current and short circuit protection when the circuit charge and discharge loop current exceeds the set value or is shorted, the short circuit detection circuit operates to turn off the MOS transistor and cut off the current. Chapter III Function Introduction of Main Parts of Protection Board

R1: reference power supply resistor; and IC internal resistor constitute a voltage divider circuit, control the internal overcharge, over-discharge voltage comparator level flip; generally in the resistance value of 330Ω, 470Ω more; when the package form (with standard components The length and width are used to indicate the component size. If the length and width of the 0402 package are 1.0mm and 0.5mm respectively, the resistance value will be numerically identified. For example, the digital identification 473 on the chip resistor indicates that it is the resistance is 47000Ω or 47KΩ (the third digit indicates the number of digits after the first two digits plus 0). R2: Over current and short-circuit detection resistors; control the current of the protection board by detecting the voltage of the VM terminal. Poor soldering and damage will cause over-current and short-circuit protection of the battery.

Generally, the resistance is 1KΩ and 2KΩ. R3: ID identification resistor or NTC resistor (described above) or both. Summary: The resistor is a black patch in the protection board. The resistance can be measured with a multimeter. When the package is large, its resistance value will be represented by a number. The method is as described above. Of course, the resistance values generally have deviations. The resistors are all accurate. If the 10KΩ resistor is +/-5%, the resistance is within the range of 9.5KΩ-10.5KΩ. C1, C2: Since the voltage across the capacitor cannot be abrupt, it acts as an instant regulator and filter. Summary: The capacitor is yellow patch in the protection board, the package form is more than 0402, there are also a few 0603 packages (1.6mm long, 0.8mm wide); the multimeter is used to detect its resistance is generally infinite or MΩ level; capacitor leakage will generate The power consumption is large, and the short circuit has no self-recovery. FUSE: Ordinary FUSE or PTC (abbreviation of Positive Temperature Coefficient, meaning positive temperature coefficient); prevent unsafe high current and high temperature discharge, wherein PTC has self-recovery function. Summary: FUSE is generally a white patch in the protection board. LITTE provides FUSE to mark the character DT on FUSE. The character indicates the rated current that FUSE can withstand. For example, the rated current of D is 0.25A, and S is 4A, T. It is 5A, etc.; now all of us are FUSE with rated current of 5A, that is, the character 'T' is identified on the body. U1: Control IC; all functions of the protection board are realized by the IC controlling the C-MOS to perform the switching operation by monitoring the voltage difference between VDD and VSS and the voltage difference between VM and VSS. Cout: Overcharge control terminal; control the MOS tube switch through the gate voltage of the MOS transistor T2. Dout: over-discharge, over-current, short-circuit control terminal; control the MOS tube switch through the gate voltage of MOSFET T1. VM: Over current and short circuit protection voltage detection terminal; over current and short circuit protection (U(VM)=I*R(MOSFET)) of the circuit is realized by detecting the voltage of the VM terminal. Summary: IC is generally a 6-pin package in the protection board.

The method of distinguishing the pins is as follows: the first pin is marked near the black dot on the package, and then rotated counterclockwise to be the second and third. 4, 5, 6 pins; if there is no black dot mark on the package, the character on the lower left side of the package is the first pin, and the other pins are counterclockwise analogous) C-MOS: field effect switch tube; protection function The achiever; continuous welding, virtual welding, false welding, breakdown will cause the battery without protection, no display, low output voltage and other undesirable phenomena. Summary: CMOS is generally a package of 8 pins in the protection board. It consists of two MOS tubes, which are equivalent to two switches, which respectively control overcharge protection and over-discharge, over-current and short circuit protection; the method of differentiation is the same as IC. Under the normal condition of the protection board, Vdd is high level, Vss and VM are low level, Dout and Cout are high level; when any parameter of Vdd, Vss, VM is changed, the level of Dout or Cout will occur. Change, at this time, the MOSFET performs the corresponding action (on and off circuit), thereby realizing the protection and recovery function of the circuit. NTC resistance test: directly measure the NTC resistance value with a multimeter, and then compare with the "temperature change and NTC resistance comparison guide". 2. Identification resistance test: directly measure the identification resistance value with a multimeter, and then compare with the "protection board important project management table". 3. Self-consumption power test: The constant current source is 3.7V/500mA; the multimeter is set to UA file, the test pen is inserted into the UA hole, and then connected with the constant current source to connect the protection board B+, B- as shown below: The multimeter's reading is the self-consumption of the protection board. If there is no reading, use the tweezers or tin wire to short-circuit the B-, P-, and activate the circuit. 4. Short-circuit protection test: The battery is connected to the protection board B+, B-, short-circuit B-, P- with tweezers or tin wire, and then short-circuit P+, P-; after short circuit, use the multimeter to measure the open circuit voltage of the protection board. Repeat 3-5 times repeatedly, the multimeter reading should be consistent with the battery, the protection board should be free of smoke, burst and other phenomena.

Connect the circuit, set the lithium easy-safe data according to the important project management table, and then press the auto button. After connecting, press the button on the red meter to test. At this time, the lamp of the Lithium Easy Tester should be lit one by one, indicating that the performance is OK. Press the display key to check the test data: 'Chg' means overcharge protection voltage; 'Dis' table over discharge protection voltage; 'Ocur' means over current protection current. No display, low output voltage, and no load: This kind of defect first excludes bad battery core (the battery has no voltage or low voltage), if the battery is bad, the protection board should be tested. The self-consumption of electricity, to see if the protection board is too large, the voltage of the battery is low. If the cell voltage is normal, it is because the entire circuit of the protection board is unreachable (component soldering, false soldering, poor FUSE, internal circuit of the PCB board, via hole, MOS, IC damage, etc.).

The specific analysis steps are as follows: First, Connect the battery core with a black meter pen, and the red meter pen is connected to both ends of the FUSE and R1 resistors, the Vdd, Dout, Cout terminals of the IC, and the P+ terminal (assuming the battery voltage is 3.8V). Analysis is done piece by piece, and these test points should be 3.8V. If not, there is a problem with this segment of the circuit. 1. There is a change in the voltage across FUSE: Test whether FUSE is turned on. If it is turned on, the internal circuit of the PCB board is unreachable. If it is not turned on, there is a problem with FUSE (bad material, over current damage (MOS or IC control failure), There is a problem with the material (FUSE is burned before the MOS or IC action), then short the wire with FUSE and continue to analyze. 2. The voltage across the R1 resistor changes: Test the resistance value of R1. If the resistance value is abnormal, it may be a virtual solder, the resistor itself is broken. If the resistance value is not abnormal, it may be a problem with the internal resistance of the IC. 3. The voltage at the IC test terminal changes: the Vdd terminal is connected to the R1 resistor. The Dout and Cout terminals are abnormal, because the IC is virtual, welding or damage. 4. If there is no change in the front voltage, the voltage between the test B- and P+ is abnormal, because the positive hole of the protection plate is not connected. (2) The red meter of the multimeter is connected to the positive electrode of the battery, and after the MOS tube is activated, the black test pen is connected to the MOS tube 2, 3 feet, 6, 7 feet, P-end. 1. MOS tube 2, 3 feet, 6, 7 pin voltage changes. It means the MOS tube is abnormal. 2. If the MOS tube voltage is not Change, the P-terminal voltage is abnormal, because the negative hole of the protection plate is not open.

Second, the short circuit is not protected: 1.VM There is a problem with the resistor: the IC2 pin can be connected with a pen of a multimeter, and the MOS tube pin connected to the VM end resistor is connected with a pen to confirm the resistance value. See if there is any solder joint between the resistor and the IC and MOS pins. 2. IC, MOS Abnormal: Since over-discharge protection and over-current and short-circuit protection share a MOS tube, if the short-circuit abnormality is due to a problem with MOS, the board should have no over-discharge protection function. 3. The above is a bad condition under normal conditions, and IC may also appear. Short-circuit abnormality caused by poor MOS configuration. As in the previous BK-901, the delay time of the IC of the model '312D' is too long, causing MOS or other components to be damaged before the IC performs corresponding action control. The easiest and straightforward way to determine whether an IC or MOS is abnormal is to replace the suspected component.

Third, the short-circuit protection has no self-recovery: (1). The IC used in the design does not have self-recovery functions, such as G2J, G2Z, etc. (2). The instrument is set to short-circuit recovery time is too short, or the load is not removed when the short-circuit test is performed. If the short-circuit test pen is short-circuited with the multimeter voltage file, the test pen is not removed from the test end (the multimeter is equivalent to a negative of several megabytes) (3). P+, P- leakage, such as rosin with impurities between the pads, yellow plastic with impurities or P+, P- capacitance is broken, ICVdd to Vss is broken down. (The resistance is only A few K to a few hundred K). 4. If there is no problem above, the IC may be broken down, and the resistance between the IC pins can be tested.

Fourth, the internal resistance is large: (1) since the MOS internal resistance is relatively stable, it appears In the case of large internal resistance. The first thing to suspect is that the internal resistance of FUSE or PTC is relatively easy to change. (2) If the resistance of FUSE or PTC is normal, the P+, P-pad and components are detected by the protection board structure. The value of via hole between the faces may cause a micro-break phenomenon in via hole and a large resistance value. (3) If there is no problem with the above, it is necessary to doubt whether the MOS is abnormal: first determine whether there is any problem with the welding; secondly, the thickness of the board (whether it is easy to bend), because the bending may cause abnormalities in the soldering of the pin; then the MOS tube Place it under the microscope to see if it breaks. Finally, use a multimeter to test the resistance of the MOS pin to see if it is broken down.

Fifth, ID anomaly: (1) The ID resistance itself is abnormal due to the virtual welding or the resistance material is not closed: the two ends of the resistor can be re-welded. If the ID is normal after re-welding, the resistance is weak soldering. If it is broken, the resistance will be cracked from it after re-welding. (2) ID via is not conductive: You can test both ends of via with a multimeter. (3)There is a problem in the internal circuit: the solder resist can be scraped off to see if the internal circuit is disconnected or short-circuited.

The page contains the contents of the machine translation.