Let's talk about the circuit principle of single-cell lithium battery protection board

qwqwqw2088

Let's talk about the circuit principle of single-cell lithium battery protection board [Copy link]

I'll find a principle of a single-cell lithium battery protection circuit and share it with you. Once the principle of single-cell lithium battery protection is understood, it will not be difficult to build a lithium battery pack, i.e. a multi-series and multi-parallel lithium battery protection board. General principle of lithium battery protection circuit The reason why lithium batteries (rechargeable) need protection is determined by their own characteristics. Since the material of the lithium battery itself determines that it cannot be overcharged, over-discharged, over-current, short-circuited, or charged and discharged at ultra-high temperatures, lithium battery components generally need to have a protection circuit. The protection function of lithium batteries is usually completed by a protection circuit board. The protection board is composed of electronic circuits. It can accurately monitor the voltage of the battery cell and the current of the charging and discharging circuit at all times in an environment of -40℃ to +85℃, and instantly control the on and off of the current circuit; The figure shows the circuit principle of general lithium battery protection. The protection board must have overcharge protection, over-discharge protection and over-current protection functions. The most basic one is composed of a voltage detection IC and two MOS tubes connected in series on the battery. The IC detects the battery terminal voltage and the MOS tube terminal voltage. The lithium battery protection board usually includes a control IC, MOS switch, resistor, capacitor and auxiliary devices NTC, ID memory, etc. The control IC controls the MOS switch to conduct when everything is normal, so that the battery cell communicates with the external circuit. When the battery cell voltage or loop current exceeds the specified value, it immediately (tens of milliseconds) controls the MOS switch to turn off to protect the safety of the battery cell. When the ambient temperature rises, the resistance of the NTC negative temperature coefficient resistor decreases, and the electrical equipment or charging equipment responds in time, controls the internal interruption and stops charging and discharging. The ID memory is often a single-line interface memory. ID is the abbreviation of Identification, which means identity recognition. It stores information such as battery type and production date. It can play a role in product traceability and application restrictions. Here are a few random single-cell lithium battery protection boards Generally, it is required that the control (IC) detects and controls the cell voltage and the working current and voltage of the charge and discharge circuit at -25℃～85℃. Under normal circumstances, the C-MOS switch tube is turned on, so that the cell and the protection circuit board are in normal working state. When the cell voltage or the working current in the circuit exceeds the preset value of the comparison circuit in the control IC, within 15～30ms (different control ICs and C-MOS have different response times), the CMOS is turned off, that is, the cell discharge or charging circuit is closed to ensure the safety of the user and the cell. The basic protection functions of a single battery are as follows: Combined with the following diagrams 1. Overcharge protection and overcharge protection recovery When the battery is charged and the voltage exceeds the set value VC (4.25-4.35V, the specific overcharge protection voltage depends on the IC), the overcharge monitoring signal Cout becomes low level, the overcharge switch MOS tube is turned off, and charging stops. When the battery voltage drops back to the set value VCR (3.8-4.1V, the specific overcharge protection recovery voltage depends on the IC), the overcharge signal becomes high level, the overcharge switch MOS tube is turned on and charging continues. VCR must be less than a fixed value of VC to prevent frequent jumps. 2. Over-discharge protection and over-discharge protection recovery When the battery voltage drops to the set value VD (2.3-2.5V, the specific over-charge protection voltage depends on the IC) due to discharge, the over-discharge monitoring signal Dout flips, and after a short delay, Dout becomes a low level, the over-discharge switch MOS tube is cut off, and the discharge stops. When the battery is placed in charging, the internal OR gate is flipped to make the MOS tube turn on again to prepare for the next discharge. 3. Overcurrent and short-circuit protection When the charging and discharging loop current exceeds the set value or is short-circuited, the short-circuit detection circuit will be activated to turn off the MOS tube and cut off the current. R1: Reference power supply resistor; forms a voltage divider circuit with the internal resistor of the IC to control the level flip of the internal overcharge and over-discharge voltage comparator; generally, the resistance value is 330Ω and 470Ω; R2: Overcurrent and short-circuit detection resistor; controls the current of the protection board by detecting the voltage at the VM end. Poor welding and damage will cause overcurrent and short circuit without protection of the battery. Generally, the resistance value is 1KΩ and 2KΩ. R3: ID identification resistor or NTC resistor or both. C1, C2: Since the voltage at both ends of the capacitor cannot change suddenly, it plays the role of instantaneous voltage stabilization and filtering. FUSE: Ordinary FUSE or PTC (positive temperature coefficient); prevents the occurrence of unsafe large current and high-temperature discharge, among which PTC has a self-recovery function. The DT mark on the FUSE indicates the rated current that can be sustained, such as D's rated current is 0.25A, S's is 4A, T's is 5A, etc.; U1: Control IC; All functions of the protection board are realized by IC controlling C-MOS to perform switching actions by monitoring the voltage difference between VDD-VSS and the voltage difference between VM-VSS. Cout: Overcharge control terminal; The switch of MOS tube is controlled by the gate voltage of MOS tube T2. Dout: Over-discharge, over-current, and short-circuit control terminal; The switch of MOS tube is controlled by the gate voltage of MOS tube T1. VM: Over-current and short-circuit protection voltage detection terminal; The over-current and short-circuit protection of the circuit is realized by detecting the voltage of VM terminal (U (VM) = I*R (MOSFET)). Under normal conditions of the protection board, Vdd is high level, Vss and VM are low level, Dout and Cout are high level; when any parameter of Vdd, Vss, and VM changes, the level of Dout or Cout will change, and at this time MOSFET performs corresponding actions (opening and closing the circuit), thereby realizing the protection and recovery functions of the circuit. When multiple batteries are connected in parallel or in series to form a battery pack, the protection circuit of the battery pack generally needs to add functions such as power display and temperature control. However, basic functions such as overcharge, over discharge, overcurrent and short circuit protection are necessary. This content was originally created by EEWORLD forum user qwqwqw2088. If you need to reprint or use it for commercial purposes, you must obtain the author's consent and indicate the source

常见泽1

Is it just to use a single chip microcomputer for testing? Now there seem to be many specialized ICs that do this.