The principle knowledge of lithium battery protection board

The principle of lithium battery protection board is very simple, electronic components are also very few, it is suitable for beginners to introduce the first chapter of the composition and main role of lithium battery protection board mainly introduces the composition of the battery protection board, the main role of the battery protection board, working principle. And the production of single lithium battery protection line application scope, electrical performance parameters, main materials, size specifications, and other items of the relevant content. All project standards described in this specification can be used as quality inspection standards and basis. (1) liquid lithium ion rechargeable battery; (2) polymer lithium ion rechargeable battery. One, the composition of the protective plate lithium battery (rechargeable) need protection, is determined by its own characteristics. Because the material of the lithium battery itself determines that it cannot be overcharged, over discharge, over current, short circuit and ultra-high temperature charge and discharge, so the lithium battery lithium battery components always follow a delicate protective plate and a piece of current protector. Lithium battery protection function is usually performed by protection circuit boards and PT synergy, protective plate is composed of electronic circuits, and 40 ℃ to + 85 ℃ under the environment of time accurate monitoring batteries voltage and circuit current and the real-time control on and off in current loop; PTC prevents severe battery damage at high temperatures.

IC, MOS switch, resistor, capacitor, and auxiliary components NTC, ID, memory, etc. Which control IC, in the case of normal MOS switch control, make batteries and external communication, and when the batteries voltage loop current or exceed the specified value, it immediately (tens of milliseconds) control MOS switch off, to protect the safety of the batteries. The NTC is the abbreviation of negative temperature coefficient, meaning that the negative temperature coefficient, when the environment temperature, the resistance is reduced, use electrical equipment or charging equipment timely response and control internal interrupt and stop charging and discharging.ID memory often for single wire interface memory, ID is the abbreviation of Identification is the meaning of Identification, storage battery types, production date and other information. Can have the traceability of products and the limitation of the application.

Role to general requirements in 25 ℃ ~ 85 ℃ when the Control (IC) testing batteries voltage Control and charge and discharge circuit of the working current, voltage, under the condition of normal C - MOS switch tube conduction, the normal work of the batteries and the protection circuit board, and when the batteries voltage or working current in the circuit exceeds comparison circuit preset Control IC, the within 15 ~ 30 ms (different Control IC and C - MOS have different response time), the CMOS shut off, shut down or charge batteries discharge circuit, to ensure the safety of users and batteries. The working principle of the second chapter protection plate protection plate working principle diagram: as shown in figure, the IC powered by batteries, voltage in 2 v to 5 v can ensure reliable work.1, overcharge protection, overcharge protection resume when the battery was charging voltage more than the set value of VC (4.25-4.35 V, voltage depends on the specific overcharge protection IC) after VD1 flip to cout is a low level, T1 cut-off, stop charging. When the battery voltage fall to VCR (3.8-4.1 V, recovery voltage depends on the specific overcharge protection IC), cout is a high level, T1 conduction charging continue, VCR VC must be smaller than a fixed value, in order to prevent frequent jump. 2, put the protection and over discharge protection resume when the battery voltage drops to set data due to discharge of VD (2.3-2.5 V, voltage depends on the specific overcharge protection IC), VD2, with short time delay, make it become a low level, dout T2 cutoff, discharge to stop, when the battery is in charge of internal or reverse the door was again and make the T2 conduction to prepare for the next discharge. 3, over current, short circuit protection when circuit loop current more than set value or is short circuit, short circuit detecting circuit, the MOS tube shut off, current cut-off. Chapter iii protection board the function of the main parts is introduced

Resistance; The voltage division circuit is formed with the internal resistance of IC to control the level flip of the internal over-charge and over-discharge voltage comparator; General in the resistance of 330 Ω, 470 Ω more; When packaging format (expressing it in standard element length and the width of the element size, such as 0402) identifies the device length and width were 1.0 mm and 0.5 mm) is larger, can use digital identifies its resistance, such as SMD resistor on digital id 473, indicates that the resistance of 47000 Ω 47 k Ω immediately (the third digit in the top two digits 0) after it. R2: overcurrent, short circuit detection resistance; By detecting the VM terminal voltage control current protection plate, welding, damage will cause the battery over current, short circuit protection, general resistance to 1 k, 2 k. R3: ID identification resistor or NTC resistor (described earlier) or both. Conclusion: the resistance in the protective plate is black patches, use multimeter can measure its value, its value when encapsulate larger numerically, said method as mentioned above, of course is proposed. Theoretical usually have deviation, each resistance has accuracy specifications, such as 10 K Ω resistance specifications for + / - 5% accuracy, its value is 9.5 K Ω - 10.5 K Ω range for qualified. C1 and C2: since the voltage at both ends of the capacitor cannot be suddenly changed, it plays the role of transient voltage stabilization and filtering. Conclusion: capacitance in the protective plate for yellow patches, 0402 packaging format is more, there are a few 0603 size (1.6 mm long and 0.8 mm wide); Multimeter is used to inspect its resistance to infinity or general M Ω level; Capacitor leakage will produce the large power consumption, short circuit without the recovery phenomenon. FUSE: ordinary FUSE or PTC (Positive Temperature Coefficient, means positive temperature coefficient); To prevent the occurrence of unsafe high discharge current and high temperature, the PTC have self-healing function. Conclusion: in the FUSE protection plate is commonly white patches, LITTE companies will provide the FUSE on the FUSE identification character D - T, rated current of the character representation meaning for the FUSE to withstand, as said D rated current is 0.25 A, S for 4 A, T, for 5 A, etc.; Now our company is all the more for rated current for 5 a FUSE, the logo on ontology and the 'T' characters. U1: control IC; Protection board all functions are IC by monitoring the connection in the VDD voltage difference between the VSS and VM - the voltage difference between the VSS C - MOS switches and control action. Cout: overcharge control end; Through the MOS pipe T2 control grid voltage MOS switch. Dout: discharge, over current, short circuit control end; Through the MOS pipe T1 control grid voltage MOS switch.VM: over current, short circuit protection voltage detection; By detecting the VM voltage circuit of over-current, short circuit protection (U (VM) = I * R (MOSFET)).Conclusion: IC in protecting plate for 6 pin form of encapsulation, commonly in the method is: the difference near the packaging logo black spots on the body as pin 1, then counterclockwise respectively 2, 3, 4, 5, and 6 pin; Identifier, such as encapsulation body without black spots are the characters on the packaging lower left as pin 1, the rest of the pin counterclockwise analogy) C - MOS: field effect switch tube; The implementer protection function; Even the welding, and virtual welding, welding, breakdown will cause the battery no protection, no display, low output voltage of unhealthy phenomenon. Conclusion: CMOS in protecting plate is commonly 8 pin form of encapsulation, it consists of two MOS tube, the equivalent of two switches, control of charge and discharge protection, over current, short circuit protection; The pin to distinguish method and IC. Under normal circumstances, the protection board Vdd for high level, Vss, VM as low level, Dout, Cout for high level; When the Vdd and Vss, VM any parameter transformation, Dout or Cout level will change, the MOSFET to perform the corresponding action (open, close circuit), so as to realize the preservation and restoration of function of the circuit. The fourth chapter main performance testing methods 1 protection board. NTC resistance test: NTC resistance value is measured with a multimeter directly, with the temperature change and the NTC resistance reference guide. 2. Identify resistance test: use multimeter direct electric resistance identification, with the protection of important project management board table of comparison. 3. Since the power consumption test: adjustable constant current source is 3.7 V / 500 ma; Multimeter is set to the uA, pens and insert the uA hole, then with constant current source in series to receive protection board B +, B, as shown in the figure below: the multimeter reading since the power consumption for the protective plate, if there is no reading with forceps or tin line B -, P - short, activate the circuit. 4. Short circuit protection test: batteries to the protection board B +, B -, use tweezers or tin line B -, P - short, sub P +, P - again; Open circuit voltage measured with a multimeter after short circuit protection board (as shown in the figure below);Sub 3-5 times repeatedly, the multimeter reading should be consistent with the batteries, protective plate should be no smoking, the phenomenon such as burst.

Good circuit, according to the important project management table set up its lithium data, press automatic button again, then good. Press the button on the red pens and after test. Light up the lamp should be successive its lithium tester, said the performance is OK. Press according to check the test data: 'Chg said overcharge protection voltage; 'Dis' table put protection voltage; 'Ocur said over-current protection current. Chapter 5 common adverse analysis a protection plate, no display, low output voltage, with no load: such a bad first ruled out bad batteries (batteries was no voltage or low voltage), if the batteries is bad should test protection board since the power consumption, since the power consumption is too large to see whether the protection plate leads to low voltage batteries. If the batteries voltage is normal, is because of the whole circuit protection board impassability components (virtual welding, welding, FUSE, PCB circuit inside the impassability, via impassability, MOS, IC damage, etc.).Specific analysis steps are as follows: (1), the multimeter black pens and batteries anode, red pens and, in turn, FUSE, R1, resistance of IC Vdd, Dout, Cout, P + side (assuming the batteries voltage of 3.8 V), piecewise were analyzed, and the several test points should be 3.8 V.If not, then this section of the circuit has a problem. 1. Both ends of the FUSE voltage change: testing whether the FUSE conduction, if the general principles of the guide is the internal PCB circuit impassability; If not the general principles of the guide there is something wrong with the FUSE (incoming bad, over-current damage (MOS) or IC control failure, material has a problem (in the MOS or IC action before the FUSE is burnt), then use wire short FUSE, continue to back analysis. 2. R1 voltage resistance change: testing R1 resistance value, if the resistance value is unusual, may be empty welding, fracture resistance itself. If resistance without exception, the problems may be the internal resistance of the IC.3. The voltage of the IC test has changed: the Vdd end connected to R1 resistor. Dout, Cout is unusual, is due to the IC virtual welding or damaged. 4. If the voltage is no change in front of the test - to the abnormal voltage between P + B, is due to protect look extremely via impassability.(2), multimeter red pens and batteries positive, after activated MOS tube, black pens and, in turn, meet the MOS tube, 2, 3 feet 6 or 7 feet, P - end. MOS tube 2 and 3 feet, 6, 7 feet voltage change, MOS tube abnormalities. 2. No change if MOS tube voltage, voltage of the P - exceptions, is due to the cathode protection plate via impassability. Two, short circuit protection: 1. The VM resistance problems: can use a multimeter pens and IC2 feet, pens and after connected to the VM resistance of MOS tube feet, confirmed its resistance value size. The resistance and IC, MOS tube feet presence of virtual welding. 2. IC, MOS anomalies: due to the discharge protection and over current, short circuit protection Shared a MOS tube, if the short circuit is abnormal, given the problems in the MOS is this plate should be done no protection function. 3. Under the normal condition for more than bad, may also appear abnormal IC with poor caused by short circuit of MOS configuration. Such as the early stage of the BK - 901, the model of "312 d" within the IC delay time is too long, cause before the IC to make corresponding action control MOS or other components have been damaged. Note: one to determine whether the IC or MOS an exception occurs the most simple, direct method is to have a suspicious components for replacement. Three, short circuit protection since the recovery: 1. The design used in IC was not self-restore function, such as G2J, G2Z, etc.2. The instrument set short recovery time too short, or short circuit test will load, short circuit such as multimeter voltage shift after the pens and sub will not pens and removed from the test end (multimeter is equivalent to a few megabytes of load).3. P +, P - leakage, such as welding plate between the impurities of rosin, cement with impurities or P +, P - capacitance is punctured, the breakdown between ICVdd to Vss. (only a few K to a few hundred K value). 4. If the above are no problem, may be breakdown, IC can test the IC value between each pin. Four, internal resistance: 1. Due to the MOS resistance is relatively stable, internal resistance big situation, the first suspect should be a FUSE or PTC whose internal resistance components is relatively easy to change. 2. If the FUSE or PTC resistance is normal, depending on the protection board structure detection P +, P - between welding plate and components surface via resistance, probably via appear slightly off phenomenon, resistance is bigger. More than 3. If no more question, will doubt whether abnormal MOS: do you have any questions first determine welding; The thickness of the second board (whether easy to bend), because when bending may lead to pin welding abnormal; Put the MOS tube in microscope observation again whether burst; Finish with a multimeter test MOS pin value, look to whether be breakdown. Five, the abnormal ID: 1. The ID resistance itself due to virtual welding, fracture or resistive material does not pass and abnormal: to welding, resistance if heavy ID is normal resistance welding, after welding if fracture resistance will be split in heavy after welding. 2. ID via conduction: not available multimeter test through holes at both ends. 3. Internal wiring problems: be scraping resistance welding paint the internal circuit disconnection, short circuit phenomenon.

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