Source: Lithium Battery Protection Board basic knowledge
First, the origin of the protection plate
Lithium-ion batteries (rechargeable) need to be protected, it is determined by its own characteristics. As the material of 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.
Lithium battery protection function is usually done by the Protection circuit Board and PTC and other current devices, the protection Board is composed of electronic circuit, in the environment of 40 ℃ to +85℃ accurate monitoring of the voltage of the cell and the current of the charging circuit, timely control of the current loop, PTC in the high temperature environment to prevent bad damage to the battery.
Second, the composition of the protection plate
Protection boards typically include control ICS, MOS switches, resistors, capacitors and auxiliary device fuse, PTC, NTC, ID, memory, and so on. wherein the control IC, under all normal circumstances to control the MOS switch conduction, so that the core and the external circuit conduction, and when the voltage or loop current of the battery exceeds the specified value, it immediately control the MOS switch off, to protect the safety of the battery.
Introduction to Protection Plate components
1, Resistance: Starting current limit, sampling effect;
2, capacitance: The Resistance value "∞" to the direct current, the resistance to alternating current is close to 0, the voltage at the end of the capacitor can not be mutated, the instantaneous voltage regulator function, the filtering effect;
3, fuse: fuse fuse, over-current protection;
4, PTC:PTC is the abbreviation of positive temperature coefficient, meaning the positive temperature coefficient resistor, (the higher the temperature, the higher the resistance), can prevent the high temperature discharge of the battery and unsafe large current, that is, over-current protection.
PTC devices using polymer polymers, through a rigorous process, made of polymer tree ester matrix and the conductive particles distributed inside the composition, under normal circumstances, conductive particles in the tree ester formed a conductive path, the device is low impedance, the circuit in the presence of overcurrent occurs, The heat generated by the large current flowing through the PTC causes the polymer-tree ester matrix to heave, thus cutting off the connection between the conductive particles, thus protecting the circuit from overcurrent. When the fault is removed, the automatic return to the initial state will ensure that the circuit is working properly.
5, NTC is negative temperature coefficient abbreviation, meaning that negative temperature coefficient, when the ambient temperature rises, its resistance decreases, the use of electrical equipment or charging equipment to respond in a timely manner, control internal interruption and stop charge and discharge.
6, the ID is identification abbreviation, namely the identity recognition meaning it divides into two kinds: one is the memory, usually is the single-line interface memory, the storage battery type, the production date and so on information; second, the identification resistor. Both can play a part in product traceability and application limitations.
① high-precision voltage detection circuit in the reservoir;
A, overcharge detection voltage (3.9V~4.4V), generally, the IC model is different, overcharge detection voltage is not the same, on the Division I now use IC, overcharge detection voltage in 4.2v~4.4v;
B, over-discharge detection voltage (2.0v~3.0v), generally, the IC model is different, over discharge detection voltage is not the same, on the Division I now use IC, overdischarge detection voltage in the 2.6v~2.8v;
② connection charger Terminal with high pressure-resistant device;
③ various delay times are realized by the internal load circuit (over-discharge, overcharge, over-current delay);
④ three-stage overcurrent detection circuit (over Circuit 1, over-current 2, load short-circuit);
⑤ charger detection function, abnormal charge current detection function;
⑥ Operating temperature range: -40℃~+85℃.
When the protection plate is normal, VDD is high, VSS,VM is low, do, CO is high, and when any of the VDD,VSS,VM parameters are changed, the level of the Do or co side will change.
About the concept of several states of the IC (usually the Co, do high level, the battery can charge and discharge)
1, overcharge detection voltage: In the usual state, the VDD gradually increased to the co driven by high level into the low vdd-vss voltage between the normal.
2, overcharge discharge voltage: In the charging state, the VDD gradually reduced to the co driven by low level to high vdd-vss between the voltage.
3, Overdischarge detection voltage: In general, VDD gradually reduced to d o driven by high level into low vdd-vss voltage between the normal.
4, Overdischarge discharge voltage: In the over-discharge state, the VDD gradually rise to do driven by low level into the vdd-vss between the high voltage.
5, over-current 1 detection voltage: In the normal state, the VM gradually rise to do from high level to low voltage between vm-vss.
6, over-current 2 detection voltage: In the normal state, the VM from the OV up to 1ms or more than 4ms speed up to do driven by high level into the low voltage between vm-vss.
7, load short-circuit detection voltage: In the normal state, the VM with ov up to 1μs above 50μs speed up to do driven by high level into low vm-vss between the voltage.
8, the Charger detection voltage: In the over-discharge state, the VM with the OV gradually down to do from low level to high voltage between the vm-vss.
9. Current consumption in normal operation: in the normal state, the current (IDD) of the VDD terminal is used as the current consumption.
10, Overdischarge consumption current: In the discharge state, the current flowing through the VDD terminal (IDD) is the overcurrent discharge consumption current.
Protection Board IC external component requirements (S81241):
1, in the R1 load than R2 small impedance occasions, because the charger connection current from the charger to ic,vdd-vss between the voltage has exceeded the maximum rating, so R1 generally less than R2.
2, if the C1 load less than 0.01μf capacitance, the load short-circuit detection, charger connection, over-current 1 and over-current 2, do is likely to occur oscillation.
3, if the R2 set resistance is less than 300 ω, when charging, the charging current may exceed the IC allowable power dissipation and damage the IC, if the R2 more than 1.3kω, the high voltage charger when charging, there can not cut off the charging power supply situation.
In figure A, MOS pins 1, 8 are connected by a MOS tube internal line or a protective board line, the foot 2 and the foot 3, the foot 6 and the foot 7 through the internal connection;
In figure II, the MOS pin D1 and D2 are connected together through the MoS tube internal lines;
In figure III, MOS pins 1, 2, 3 are connected through an internal line, and MOS pins 5, 6, 7, 8 are connected through an internal line.
Naming rules for IC and MOS pipe pins
In general, two-column electronic components of the PIN name are in accordance with anti-clockwise naming rules, IC, MOS tube is no exception. This generally consists of two types: 1, if the component has a small circle concave point on the pin is 1 feet, the rest of the counter-clockwise arrangement (Figure A), 2, if there is no concave point, but there is text (usually the component model), the component is placed to the normal reading and writing state, (Figure 2) the left side of the text below the first pin 1 feet The rest is arranged in a counterclockwise order.
Three, the protective plate of several practical indicators
Definition: The conduction impedance of the MoS tube when the charging current is 500mA.
Due to the high frequency of communication equipment, data transmission requirements of low bit error rate, its pulse string rise and fall along the steep, so the battery's current output capacity and voltage stability requirements, so the protection of the MOS transistor switch on the resistance to small, single-power-saving core protection plate is usually in <70mω, If too General Assembly cause communication equipment work is not normal, such as mobile phone in the call suddenly disconnected, telephone connection, noise and other phenomena.
2. Self-draining flow
Definition: IC operating voltage is 3.6V, in no-load state, flow through the protection IC operating current, generally very small.
The self-draining flow of the protective plate directly affects the battery's standby time, which usually stipulates that the self-draining current of the protection plate is less than 10 micro-Ann.
3. Current capability
As a protective device for lithium-ion batteries, the protection plate can work reliably within the normal operating current range of the equipment, and can act quickly when the battery is accidentally shorted or overcurrent, so that the core is protected.
5, mechanical properties, temperature adaptability, antistatic ability
The protection plate must be able to pass the national standard Vibration, the impact test; the protection plate can work safely in the 40-85 ℃ and can withstand the non-contact ESD electrostatic test of ±15kv.
Four, single power-saving core Protection Board circuit principle and work process
General Protection Board schematic (typical)
Protection plate schematic diagram (simplified diagram)
How the Protection plate works
, the IC is powered by an electric core, and the voltage is guaranteed to work reliably in 1.5v-10v.
1, the usual status: battery voltage over discharge detection voltage above (2.75V above), overcharge detection voltage below (4.3V), the voltage of the VM terminal in the charger detection voltage above, in the case of over-current/detection voltage (OV), IC by monitoring the voltage difference between the Vdd-vss and the voltage difference between the Vm-vss control MOS tube, do, CO end are high level, MOS tube conduction state, then can be free charge and discharge;
2, overcharge protection
When the battery is charged so that the voltage exceeds the SetPoint VC (4.25-4.35v), the VD1 rollover causes the cout to become low, the T1 cutoff, the charge stop, and when the battery voltage falls back to the VCR (3.8-4.1v), cout becomes high, T1 conduction charge continues, the VCR is less than the VC a fixed value, To prevent frequent jumps in the current.
3, over-discharge protection
When the battery voltage is reduced to the SetPoint VD (2.3-2.5v) due to discharge, the VD2 flips to the IC fixed short time delay, so that the dout into low level, T2 cutoff, discharge stop.
4, over-current, short-circuit protection
When the circuit discharge current exceeds the set value or the output is shorted, the overcurrent, short-circuit detection circuit action, so that the MoS tube (T2) shutdown, the current cut-off.
Five, multi-power-saving core Series Protection Board circuit principle and working process
1. Schematic diagram
Same as the single power-saving core, in the multi-energy-saving core protection circuit, the protection board must also be able to provide overcharge, over-discharge, over-current, short-circuit protection.
Dual power-saving core protection board schematic diagram
Six, general Protection Board Bad Reason analysis method
1, no display (no voltage, charging, no load voltage low): When the battery is found no display, you can take the following steps to analyze (tool: multimeter):
① first with a multimeter to measure the positive and negative voltage of the core, such as the voltage is normal when the battery, the protection plate has a problem, enter step b; If the cell voltage or voltage is low, then the protection plate static current (self-power), the current is less than 10μa, then the core has a problem, if the current is greater than 10μa, The protection plate is defective.
② If there is a problem with the protection board, you can use a multimeter black pen always contact the cathode, Red pen instrument on both ends of FUSE, 471 resistors at both ends, the VDD end of the IC, do end, CO end measurement voltage, if the protection plate is good, Assuming that the core voltage is 3.8V, then the voltage value in these places should also be 3.8V, if the voltage is not 3.8V, the following methods can be used to find the reason:
A, fuse both ends of the voltage changes, can be used to test whether the fuse conduction multimeter, if the general is fuse broken, or wire to fuse short, and then test the hardware (wire) p+, p-between the voltage, if there is a fuse break, and then can be used million and the table 20A Test battery has no short-circuit protection, If there is short-circuit protection, fuse may be bad for the incoming, there may be damage to the operation, such as the absence of short-circuit protection, should be the MOS Tube discharge control terminal problems or the problem of the IC VM side, the specific analysis methods see no Protection analysis method.
B, if the voltage at the end of the 471 resistor changes, you can take the following method analysis: First with a multimeter ω Test 471 resistance is normal, if the resistance is not normal can be used soldering iron resistance ends, such as the resistance for the virtual welding should be able to return to the normal resistance, if the resistance does not return to the regular value, then can be branded See if the resistance is broken, such as fracture, you should trace where the fault. If the resistance is not false welding, and no break, you should trace the incoming have no problem. If the resistance value is normal, the IC or MOS tube should be abnormal to cause 471 resistance voltage reduction, the specific analysis method see "C".
C, if the front fuse, 471 resistors are no problem, the problem may be due to the IC and MOS tube this pair of mating elements, including several cases:
A, the components of the virtual welding: can be welded iron-welded mos or IC feet, if the components of the virtual should be able to weld good;
B, component damage, can be used to replace the components or measuring the resistance between the components of the method to determine.
D, if the fuse, 471 resistance, IC, MOS tube voltage has not changed, the use of multimeter red pen contact positive, black pen contact MOS Tube 2, 3 feet or MOS tube 5, 6 feet. If the voltage is constant, then the hardware p+, p, if no voltage, it should be the protection plate through the hole. If you want to determine whether the positive or negative through the hole is not through, you can use the universal table pen one to connect the core one pole (b + or B), the other one to connect the hardware (p+ or P) to determine.
2, no short-circuit protection: If the battery is not short-circuit protection, you can be analyzed from the following several situations:
A, the problem of the VM side resistor, can be used multimeter a pen to contact the VM side of the IC, another pen contact with the VM side resistor connected to the MOS tube part (ie, P-pin), confirm the resistance value, if there is a problem with resistance, then use a soldering iron to determine the resistance of the false welding, fracture, or the issue of
B, MOS Tube discharge control terminal can not be closed, to determine whether the MoS tube problems, the simplest way is to use a good protection plate (a) MOS tube to replace the bad protection Plate (B) on the MoS tube, but also the replacement of the MOS tube onto the protection plate (a). If the two protection plates are OK, should be MOS tube virtual welding, if the protection plate (b) is OK, and the protection Plate (a) NG, the protection Plate (b) on the thick MOS tube bad, if the protection plate (b) is NG, and the protection Plate (a) is OK, the protection Plate (b) on the original IC has a problem. Another method is to determine by measuring, generally in the absence of voltage, good mos pin R14, R24 between the resistance of 10mω, R21 (or R31) between a resistance of one to 10mω, the multimeter in a different direction, it should be about dozens of Ω.
3, discharge poor (load voltage is low): if the battery discharge is bad can be from the following several situations to analyze:
A, the electric core load voltage is low, can be used multimeter with 5w10ω load direct measurement of the positive and negative electrode, to confirm whether the core with load voltage can meet the standard, the general voltage is lower than the standard value is not a lot, may recharge, put a few days re-check OK can be shipped.
B, protection plate with no load, the analysis method is: Multimeter with 5w10ω load, with red pen contact cathode fixed, black pen contact MOS Tube 2 (3) and foot 5 (6), verify that the multimeter reading has no change, if there is a change in the MoS tube problem, The MoS pin can be re-welded with soldering iron to confirm whether the pin is not welded, but also to determine the resistance between the MOS pin (the method with no display of "C"), if the MoS tube at both ends with load reading no change, and hardware p+, p-End with load not up to the requirements or reading zero, The protection plate should not pass through the hole (its analysis method with no display of "D").
4, ID exception: for the General Protection Board (in addition to AX940, Hi777, T6, T100, T6890), id back to the road, only a loop resistor, if the ID has an exception can be analyzed in several cases:
A, the ID resistance itself due to short-circuit, false welding, fracture or due to resistance material irregularities and abnormal. If the ID itself is a problem, you can use the soldering iron to determine whether the resistance is short-circuit, false welding, fracture or resistance material problems, such as the false welding resistance will become normal, such as the break resistance will drop half.
B, the ID resistor itself is not a problem, and the hardware ID and P-between the resistance of the abnormal may be over the hole or the protection board on the circuit is short-circuited.
5, NTC Anomaly: General Protection Plate NTC circuit only one NTC resistor, if the NTC anomaly analysis method and ID anomaly analysis method.
Protection plate inspection and operation precautions
Ii. precautions for processing and using protective plates
1, the generation of electrostatic
3, how to reduce the occurrence of static electricity
(b), high temperature protection
Basic knowledge of lithium battery Protection Board (RPM)