Principle knowledge of lithium battery protection Board

Lithium battery Protection Board principle is very simple, electronic components are also few, more suitable for beginners under the first chapter of the composition and main role of the protection plate mainly introduces the composition of the lithium battery Protection Board, the main role of battery protection plate, working principle. As well as the production of a single lithium battery protection line application range, electrical performance parameters, major materials, size specifications, and other items related to the content. All the project standards described in this specification can be used as quality inspection standards and basis. 2 Range of applications (1) Liquid lithium-ion rechargeable battery, (2) Polymer lithium-ion rechargeable battery. First, the formation of the protective plate lithium battery (rechargeable type) is required to protect, is determined by its own characteristics. As the lithium battery itself determines that it can not be overcharge, over discharge, over-current, short-circuit and ultra-high temperature charge and discharge, lithium battery components will always follow a delicate protection plate and a piece of current safety device appears.

The protection function of lithium battery is usually done by the Protection circuit board and PT. The protection Board is composed of electronic circuit, in the environment of 40 ℃ to +85℃ to monitor the voltage of the electric core and the current of the charging circuit, to control the current circuit, and to prevent the bad damage of the battery in the high-temperature environment.

1. The protection board usually includes control IC, MOS switch, resistor, capacitance and auxiliary device NTC, ID memory and so on. The control IC, in all normal circumstances control MOS switch conduction, so that the electric core and external circuit communication, and when the core voltage or loop current exceeds the specified value, it immediately (dozens of milliseconds) control MOS switch off, protect the safety of the battery. NTC is the abbreviation of the negativetemperaturecoefficient, meaning that the negative temperature coefficient, when the ambient temperature rises, its resistance reduced, the use of electrical equipment or charging equipment in a timely manner to control the internal interruption and stop charging and discharging. ID memory is often a single line interface memory, ID is the abbreviation of identification is the meaning of identification, storage battery type, production date and other information. Can be a product traceability and application of the restrictions

2. The main role of the protection plate.

General requirements in the -25℃~85℃, control (IC) check the voltage and charge and discharge circuit of the operating current, voltage. Under all normal conditions C-MOS switch pipe conduction, so that the electric core and Protection circuit board in the normal working state, and when the electric core voltage or circuit in the operating current over the control IC comparison circuit defaults, in the 15~30ms (different control IC and C-MOS have different response time), the C-MOS off, That is to turn off the electric core discharge or charging circuit to ensure the safety of the user and the batteries. The working principle of the protection board: as shown in the diagram, the IC is powered by the battery, and the voltage in the 2v-5v can ensure reliable work. 1, overcharge protection and overcharge protection when the battery is charged to the voltage over the set value of VC (4.25-4.35v, the specific overcharge protection voltage depends on the IC), VD1 flip to make cout into a low level, T1 cut-off, charging stop. When the battery voltage falls back to the VCR (3.8-4.1v, Specific overcharge protection recovery voltage depends on IC), cout into a high level, T1 conduction charge continue, VCR must be less than VC a fixed value to prevent frequent jumps. 2, Over-discharge protection and over-release protection recovery when the battery voltage is lowered to the set value due to discharge of VD (2.3-2.5v, specific overcharge protection voltage depends on the IC), VD2 Flip, with a short time delay, so that the dout into a low level, T2 cut-off, discharge stop, when the battery is placed on the charge, the interior or door is flipped to make T2 again conduction for the next discharge for good Get ready. 3, over-current, short-circuit protection when the circuit full discharge circuit current exceeds the set value or short circuit, short-circuit detection circuit action, so that MoS tube off, current cut-off

3. Function introduction of main parts of protection board

R1: The benchmark power supply resistance, and IC internal resistance constitutes a partial voltage circuit, control the internal overcharge, over discharge voltage comparator's level reversal, generally in the resistance for 330ω, 470ω more; When the package form (that is, the length and width of the standard components to represent the size of the component, If the 0402 package identifies the length and width of this component to be 1.0mm and 0.5mm respectively, it will use a number to identify its resistance, such as SMD resistor on the digital ID 473, which means that its resistance is 47000ω namely 47kω (the third digit is the first two digits followed by 0 digits). R2: overcurrent, short-circuit detection resistance, through the detection of VM Terminal Voltage control protection plate current, welding bad, damage will cause battery over-current, short-circuit unprotected, general resistance for 1kω, 2kω more. R3:id identification resistors or NTC resistors (described above) or both. Summary: Resistors in the protection plate for black patches, with a multimeter to measure its resistance, when the package is larger when its resistance will be used to indicate the method as described above, of course, resistance generally have deviations, each resistance has precision specifications, such as 10kω resistance specifications for +/ -5% accuracy of its resistance for 9.5kω-10.5kω range are qualified. C1, C2: Because the capacitor voltage at both ends can not mutate, the instantaneous voltage regulator and filter action. Summary: Capacitor in the protection plate for yellow patches, packaging form more than 0402, there are a few 0603 packages (1.6mm long, 0.8mm wide); Use a multimeter to detect its resistance is generally infinite or mω level; capacitance leakage will produce a large power consumption, short-circuit without self recovery phenomenon. FUSE: Ordinary FUSE or PTC (positivetemperaturecoefficient abbreviation, meaning positive temperature coefficient); Prevent the occurrence of unsafe high current and high temperature discharge, in which PTC has the function of self recovery. Summary: Fuse in the protection board generally for white patches, litte company to provide fuse will be in fuse superscript d-t, characters mean that fuse can withstand the rated current, If the D-rated current is 0.25a,s for 4a,t 5 A and so on, we are all more than the rated current of 5 a fuse, that is, in the body marked "T". U1: Control IC, Protection board all functions are IC by monitoring the connection between the voltage difference between the Vdd-vss and Vm-vss voltage difference between the control C-mos perform switch action to achieve. Cout: overcharge control end, through MOS tube T2 gate voltage Control mos tube switch. Dout: Over discharge, over-current, short-circuit control terminal, through MOS tube T1 gate voltage Control mos tube switch. VM: overcurrent, short-circuit protection voltage detection end, through the detection of VM-side voltage to achieve circuit overcurrent, short-circuit protection (U (VM) =i*r (MOSFET)). Summary: IC in the protection Board is generally 6 pin packaging form, the difference between the pin's method is: In the package, marking the black spot near the 1th pin, and then counterclockwise rotation of the 2nd, 3, 4, 5, 6 pins, if the package is no black dot logo, the package is looking at the characters on the lower left for the 1th pin, The rest of the pins are counterclockwise. C-mos: Field effect switch tube, the protection function of the realization of welding, virtual welding, false welding, breakdown will result in battery unprotected, no display, low output voltage and other undesirable phenomena. Summary: CMOS in the protection board is generally 8 pin package form, it is composed of two MoS tube, the equivalent of two switches, respectively, control overcharge protection and over-current, over-current, short-circuit protection, the pin is differentiated by the same method and IC. Under normal conditions of the protection plate, the VDD is high level, VSS, VM is low level, dout, cout is high level, when any parameter of VDD, VSS, VM changes, the level of dout or cout will change, at this time the MOSFET executes the corresponding action (open and close the circuit), In order to realize the circuit protection and recovery function. The fourth chapter the main performance test method of the protective board 1. NTC resistance test: direct measurement of NTC resistance with a multimeter, compared with the "Temperature change and NTC resistance control Guide." 2. Identification resistance test: Using the multimeter to directly measure the identification of resistance value, and the "Protection Board important project management table" comparison. 3. Self-consumption test: adjust constant flow source for 3.7v/500ma; multimeter set to UA file, the table pen is inserted into the UA connector and then connected to the constant current source to connect the protection plate B +, B.-as shown in the following illustration: At this time, the multimeter reading is the protection Board of the power consumption, such as no reading with tweezers or tin line short B, p, activate the circuit. 4. Short Circuit protection test: The electric core receives the protection Board B-B, use tweezers or tin line short connect B, p, short connect p+, p; After short-circuit, use multimeter to measure the open circuit voltage of the protective plate (shown below); repeated short 3-5 times, at this time the multimeter reading should be consistent with the battery, the protection board should not smoke, burst and other phenomena.

As shown in the above diagram to connect the circuit, according to the important Project management table set good lithium easy data, and then press the Automatic button, and then press the button on the Red pen to test. At this time, lithium easy safety tester lights should be lit, indicating performance OK. Press the display key to check the test data: ' CHG ' indicates overcharge protection voltage, ' Dis ' table overcurrent protection voltage, ' ocur ' indicates overcurrent protection current. Fifth chapter common adverse analysis of protection Board no display, low output voltage, with no load: this kind of bad first out of the battery (the battery has no voltage or low voltage), if the bad core should be tested to protect the plate from the power consumption, to see whether the protection plate since the excessive consumption of electricity led to low voltage. If the core voltage is normal, it is because the entire circuit of the protection Board is not through (components virtual welding, false welding, fuse, PCB board internal circuit, over hole, MOS, IC damage, etc.). The detailed analysis steps are as follows: (a), with a multimeter black table pen to connect the cathode, Red table pen to connect fuse, R1 resistor at both ends, IC VDD, Dout, cout end, p+ end (assuming the voltage of the core is 3.8V), the analysis by paragraph, this several test points should be 3.8V. If not, there is a problem with this circuit. 1.FUSE voltage changes at both ends: test whether the fuse conduction, if the guide general is PCB Board internal Circuit, if the general rules fuse problems (poor incoming, over-current damage (MOS or IC control failure), material problems (in MOS or IC action before the fuse burned), Then use the wire short connect fuse, continue to analyze. 2.R1 resistance voltage changes at both ends: Test R1 resistance value, if the resistance value is abnormal, it may be virtual welding, the resistance itself broken. If the resistance value is not abnormal, it may be the IC internal resistance problem. 3.IC Test End voltage change: Vdd end is connected with R1 resistor. Dout, cout end of the anomaly, is due to the IC virtual welding or damage. 4. If the front voltage does not change, test B-to p+ voltage anomaly, it is because the protection plate positive through hole. (b), multimeter red table pen to connect the cathode, activated MOS tube, black pen in turn to connect MOS Tube 2, 3 feet, 6, 7 feet, p-end. 1.MOS Tube 2, 3 feet, 6, 7 feet voltage changes, which means that the MOS tube abnormal. 2. If the MoS tube voltage does not change, the P-terminal voltage is abnormal, it is because the protection plate cathode is not through the hole. Second, short-circuit no protection: 1. VM Side Resistance problem: You can use a multimeter a table pen IC2 foot, a table pen and the VM end resistance connected MOS pipe PIN, confirm its resistance value size. See Resistance and IC, MOS pin has no virtual welding. 2.IC, MOS anomaly: due to over-current protection and over-current, short-circuit protection common to a MOS tube, if the short-circuit anomaly is due to MOS problems, then this board should have no protection function. 3. The above is the normal condition of the bad, may also appear IC and MOS configuration caused by the short circuit anomaly. such as the early appearance of the BK-901, its model is ' 312D ' in the IC delay time is too long, resulting in the IC to make the corresponding action control MOS or other components have been damaged. Note: The most simple and direct way to determine whether an IC or MOS is abnormal is to replace a suspected component. Third, short-circuit protection without self-recovery: 1. The IC used in the design has no self recovery function, such as g2j,g2z. 2. The instrument set short circuit recovery time is too short, or short-circuit test did not remove the load, such as using a multimeter voltage file for short circuit table pen and then did not remove the pen from the test end (multimeter equivalent to a few megabytes of load). 3.p+, p-leakage, such as between the pads with impurities in the rosin, with impurities in the yellow gum or p+, p-capacitance is penetrated, icvdd to the VSS between the breakdown. (Resistance is only a few k to hundreds of K). 4. If none of the above problems, may be the IC breakdown, can test IC pin resistance between the feet. Four, internal resistance: 1. Due to the relatively stable MOS resistance, the emergence of large internal resistance, the first suspicion should be fuse or PTC these internal resistance relatively easy to change the components. 2. If the fuse or PTC resistance is normal, the visual protection plate structure to detect p+, p-pad and component surface between the Kong value, may have a micro-broken hole phenomenon, the resistance is greater. 3. If there are no more problems, there is a question of whether MOS is abnormal: first determine if there is a problem with the weld, and then the thickness of the kanban (whether it is easy to bend), because bending may lead to abnormal welding of the pins, and then the MOS tube under the microscope to see if the rupture, and finally the MOS pin resistance test To see if it was penetrated. Five, ID abnormal: 1.ID resistance itself due to virtual welding, fracture or due to resistance material does not pass through the exception: can be welded at both ends of the resistance, if the normal ID after the welding is resistance to virtual welding, if the fault resistance will be in the reflow after the rupture. 2.ID over Hole does not guide: the use of a multimeter test over the hole ends. 3. Internal wiring problems: can scrape open solder paint to see if the internal circuit is disconnected, short-circuit phenomenon.

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