Function introduction of main parts of lithium battery protection board shared by 18650 rechargeable lithium battery supplier.
R1: reference power supply resistance; With IC internal resistance to form voltage divider circuit, control the internal overcharge, overdischarge voltage comparator level reversal; 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 and 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 Ω Ω resistance to 1 k, 2 k. R3: ID resistance or NTC resistance (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, C2: since the voltage at both ends of the capacitor cannot mutate, it plays the role of instant voltage stabilization and filtering.
Conclusion: the capacitor of the High temperature resistance lithium ion battery is a yellow patch in the protective plate, with a few 0603 packages (1.6mm long and 0.8mm wide) and a few 0402 packages. Multimeter is used to inspect its resistance to infinity or general M Ω level; Capacitor leakage will produce large self - consumption, short - circuit no self - recovery phenomenon. FUSE: ordinary FUSE or PTC (abbreviation of Positive Temperature Coefficient) prevents unsafe large current and high Temperature discharge, in which PTC has self-recovery function.
Conclusion: FUSE is usually A white patch in the protective plate. LITTE company provides FUSE with the character d-t on FUSE, which means the rated current FUSE can withstand, such as D rated current 0.25a, S 4A, T 5A, etc. At present, most of our FUSE devices with rated current 5A are identified as' T 'on the ontology.
U1: control IC; All functions of protection board are realized by IC controlling c-mos to perform switch action by monitoring voltage difference between vdd-vss and vm-vss.
Cout: overcharge control terminal; The MOS switch is controlled by MOS T2 gate voltage.
Dout: over discharge, over current, short circuit control end; The switch of MOS tube is controlled by the gate voltage of MOS tube T1.
VM: overcurrent and short-circuit protection voltage detection terminal; The overcurrent and short circuit protection of the circuit (U (VM) =I*R (MOSFET)) is realized by detecting the voltage at the VM end.
Conclusion: IC is generally in the packaging form of 6 pins in the protection board. The way to distinguish the pins is as follows: the first pin is near the black spot marked on the packaging body, and then the second pin, third pin, fourth pin, fifth pin and sixth pin are rotated counterclockwise. If there is no black dot mark on the packaging body, the bottom left of the characters on the packaging body is the first pin, and the rest of the pins are analogically counterclockwise. The implementor of the protection function; Continuous welding, false welding, false welding, breakdown will cause the battery without protection, no display, low output voltage phenomenon. Conclusion: in the protection board, CMOS is usually in the package form of 8 pins. It is composed of two MOS tubes, equivalent to two switches, which control overcharge protection, overdischarge protection, overcurrent protection and short-circuit protection respectively. The pin distinguishing method is the same as IC. Under normal circumstances, Vdd is high level, Vss and VM are low, and Dout and Cout are high. When any of the parameters of Vdd, Vss and VM are transformed, the level of Dout or Cout will change. At this time, MOSFET performs corresponding actions (on and off circuit), so as to realize the protection and recovery function of the circuit.