The function introduction of the main parts of the protection board
R1: Reference power supply resistance; forms a voltage divider circuit with the internal resistance of the IC to control the level inversion of the internal overcharge and overdischarge voltage comparator; generally the resistance value is 330Ω and 470Ω; when the package form (that is, the standard component The length and width indicate the size of the component. For example, the length and width of the 0402 package mark are 1.0mm and 0.5mm, respectively.) When it is larger, the resistance value will be marked by numbers. For example, the number mark 473 on the chip resistor indicates its resistance. The resistance value is 47000Ω or 47KΩ (the third digit represents the digit with 0 after the first two digits).
R2: Over-current and short-circuit detection resistance; the current of the protection board is controlled by detecting the voltage of the VM terminal. Poor welding or damage will cause the battery to over-current and short-circuit without protection. The general resistance values are 1KΩ and 2KΩ.
R3: ID identification resistor or NTC resistor (described earlier) or both.
Summary: The resistance is a black patch in the protection board. The resistance value can be measured with a multimeter. When the package is large, the resistance value will be represented by numbers. The method of expression is as described above. Of course, the resistance value of All resistors have precision specifications. For example, if the 10KΩ resistance specification is +/-5% accuracy, the resistance value is within the range of 9.5KΩ to 10.5KΩ.
C1, C2: Since the voltage at both ends of the capacitor can't change suddenly, it plays the role of instant voltage stabilization and filtering. Summary: The capacitor is a yellow patch in the protection board. There are many types of 0402 packages, and there are also a few 0603 packages (1.6mm long and 0.8mm wide); the resistance value of the multimeter is generally infinite or MΩ level; the leakage of the capacitor will be generated from High power consumption, no self-recovery in short circuit. FUSE: Ordinary FUSE or PTC (abbreviation of Positive Temperature Coefficient, meaning positive temperature coefficient); to prevent unsafe high current and high temperature discharge from occurring, among which PTC has a self-recovery function.
Summary: FUSE is generally a white patch in the protection board. The FUSE provided by LITTE will mark the character DT on FUSE. The character means the rated current that FUSE can withstand. For example, it means that the rated current of D is 0.25A, S is 4A, T For 5A and so on.
U1: Control IC; all functions of the protection board are realized by the IC by monitoring the voltage difference between VDD-VSS and the voltage difference between VM-VSS and controlling the C-MOS to perform switching actions.
Cout: Overcharge control terminal; the switch of the MOS tube is controlled by the gate voltage of the MOS tube T2.
Dout: Over-discharge, over-current, short-circuit control terminal; control the switch of MOS tube through the gate voltage of MOS tube T1.
VM: Over-current and short-circuit protection voltage detection terminal; realize circuit over-current and short-circuit protection by detecting the voltage of VM terminal
Summary: IC in the protection board is generally a 6-pin package, the method of distinguishing the pins is: the first pin is marked near the black dot on the package body, and then the second pin is rotated counterclockwise. , 4, 5, 6 pins; if there is no black dot mark on the package body, look at the lower left of the characters on the package body as the first pin, and the remaining pins are analogously counterclockwise) C-MOS: field effect switch tube; protection function Realizers; continuous welding, virtual welding, false welding, and breakdown will cause unprotected batteries, no display, low output voltage and other undesirable phenomena.
Summary: CMOS is generally an 8-pin package in the protection board. It is composed of two MOS tubes, which are equivalent to two switches, which control overcharge protection and overdischarge, overcurrent, and short circuit protection respectively; its pins The distinction method is the same as IC.
Under normal conditions of the protection board, Vdd is high, Vss, VM are low, Dout, Cout are high; when any parameter of Vdd, Vss, VM is changed, the level of Dout or Cout will occur Change, at this time the MOSFET performs corresponding actions (opening and closing the circuit), so as to realize the protection and recovery function of the circuit.