Fast-off circuit based on lithium battery protection board

Abstract

The utility model discloses a quick turn-off circuit based on lithium battery protection board, the lithium battery protection board includes protection chip U1, and the discharge control pin DHC of protection chip U1 is connected the discharge MOS pipe group on the control lithium battery charging line, and the discharge MOS pipe group is in parallel by a plurality of discharge MOS pipe and is formed, the quick turn-off circuit includes triode Q17, and the emitter of triode Q17 is connected the grid of each discharge MOS, and the base is connected chip U1's DHC pin, and the collector is through resistance R70 and is grounded, and the diode D3 between the emitter and the base is added, and the potential difference between the base and the emitter is formed, guarantees triode Q17 can normally turn on. The utility model discloses through the quick conduction characteristic of triode Q17, when the DHC pin output low level of protection chip U1, rapidly pulls down all parallel MOS's grid voltage, ensures multiple MOS synchronous turn-off, effectively prevents the current concentration problem caused by turn-off delay, reduces the risk of local overcurrent and thermal breakdown.

Description

Technical Field

[0001] This utility model relates to the field of lithium battery protection technology, and in particular to a fast shutdown circuit based on a lithium battery protection board. Background Technology

[0002] In high-current BMS, the charging and discharging switches often use multiple MOS transistors connected in parallel to amplify the current. However, the threshold voltage (Vth), transconductance (Gm), and parasitic parameters of the MOS transistors differ. After the turn-off command is issued, some MOS transistors turn off with a delay, causing current to concentrate in the delayed turn-off MOS transistors, leading to local overcurrent and thermal breakdown. Traditional gate drive resistor optimization methods cannot solve the problem of asynchronous turn-off, which can easily damage the devices.

[0003] Traditional gate drive resistor optimization methods struggle to balance turn-off speed and anti-oscillation requirements, failing to effectively address turn-off asynchrony issues. While independent driver solutions can improve synchronization performance, they significantly increase system cost and layout complexity.

[0004] Maintaining system stability and cost-effectiveness while ensuring shutdown speed has become a pressing technical challenge in this field. Utility Model Content

[0005] The purpose of this invention is to provide a low-cost, high-reliability fast turn-off circuit that forces multiple parallel MOS transistors to turn off synchronously and quickly, thereby eliminating the risk of dynamic current imbalance.

[0006] The technical solution of this utility model is:

[0007] Based on the fast shutdown circuit of the lithium battery protection board, the lithium battery protection board includes a protection chip U1. The discharge control pin DHC of the protection chip U1 is connected to control the discharge MOS transistor group on the lithium battery charging line. The discharge MOS transistor group is composed of multiple discharge MOS transistors connected in parallel.

[0008] The fast shutdown circuit includes a transistor Q17. The emitter of the transistor Q17 is connected to the gate of each discharge MOS, the base is connected to the DHC pin of chip U1, and the collector is grounded through resistor R70. A diode D3 is added between the emitter and the base to form a potential difference between the base and the emitter, ensuring that the transistor Q17 can conduct normally.

[0009] Preferably, the transistor Q17 is a PNP type transistor.

[0010] Preferably, the anode of diode D3 is connected to the base of transistor Q17, and the cathode of diode D3 is connected to the emitter of transistor Q17.

[0011] Preferably, when the DHC pin of the protection chip U1 is working normally, it outputs a high level, at which time Q17 is in the off state.

[0012] Preferably, when the DHC pin of the protection chip U1 outputs a low level, the transistor Q17 is turned on, and the gate current of the discharge MOSFET flows to the resistor R70 connected to the collector of the transistor Q17, which consumes the current, so that the gate voltage of the MOSFET is quickly pulled down to achieve complete shutdown of the discharge MOSFET.

[0013] Preferably, the resistance R70 is adjusted according to the gate charge of the MOS: 1kΩ~10kΩ.

[0014] The advantages of this utility model are:

[0015] 1. The fast turn-off circuit based on the lithium battery protection board provided by this utility model utilizes the fast conduction characteristics of transistor Q17 to quickly pull down the gate voltage of all parallel MOS when the DHC pin of the protection chip U1 outputs a low level, ensuring that multiple MOS are turned off synchronously, effectively preventing current concentration problems caused by turn-off delay, and reducing the risk of local overcurrent and thermal breakdown.

[0016] 2. Compared with the independent driver solution, this utility model only requires the addition of a PNP transistor, a resistor and a diode, which is simple in structure and low in cost, and does not affect the stability and reliability of the system. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0018] Figure 1 The schematic diagram of the fast shutdown circuit based on the lithium battery protection board provided by this utility model. Detailed Implementation

[0019] The fast shutdown circuit of this invention is applied to a lithium battery protection board (BMS) and mainly includes the following core components:

[0020] Protection chip U1: Responsible for monitoring battery status and outputting control signals. Its discharge control pin (DHC) is used to control the switching of the discharge MOSFET.

[0021] Discharge MOSFET group (Q1~Q12): Composed of multiple N-channel MOSFETs connected in parallel, used to control the on / off state of the battery discharge circuit.

[0022] Fast shutdown module: Composed of PNP transistor Q17 (model MMBT4403), resistor R70 (package 1206) and diode D3 (model IN4148WX), used to force synchronous shutdown of MOSFET group.

[0023] The emitter of transistor Q17 is connected to the gate of all discharge MOSFETs (Q1~Q12), and the base is connected to the DHC pin of protection chip U1. The collector is grounded through resistor R70 (typically 10kΩ).

[0024] The anode of diode D3 is connected to the base of Q17, and the cathode is connected to the emitter of Q17 to ensure a forward bias voltage between the base and emitter, so that Q17 can conduct normally.

[0025] Normal operating state (DHC=high level): The DHC pin of the protection chip U1 outputs a high level (e.g., 5V). Q17 is cut off because the base voltage is higher than the emitter voltage, which does not affect the normal conduction and turn-off of the MOS transistor group.

[0026] Fast shutdown state (DHC=low level): When U1 detects faults such as overcurrent or over-discharge, the DHC pin outputs a low level (0V).

[0027] Because of the gate capacitance of the MOSFET group (Q1~Q12), the gate voltage will not drop immediately. At this time, the emitter voltage (≈Vgs) of Q17 is higher than the base voltage (0V), and Q17 is turned on. The gate charge is quickly discharged to ground through Q17 and R70, forcing all MOSFETs to turn off synchronously and avoiding the current concentration problem caused by turn-off delay.

[0028] If the resistance of resistor R70 is too small, the turn-off speed will be too fast, which may cause voltage oscillation; if the resistance is too large, the turn-off efficiency will be reduced. The recommended value for resistor R70 is 1kΩ~10kΩ, which should be adjusted according to the gate charge of the MOS transistor.

[0029] The above embodiments are only for illustrating the technical concept and features of this utility model, and are intended to enable those skilled in the art to understand the content of this utility model and implement it accordingly. They should not be construed as limiting the scope of protection of this utility model. All modifications made in accordance with the spirit and essence of the main technical solution of this utility model should be included within the scope of protection of this utility model.

Claims

1. A fast shutdown circuit based on a lithium battery protection board, characterized in that, The lithium battery protection board includes a protection chip U1. The discharge control pin DHC of the protection chip U1 is connected to control the discharge MOS transistor group on the lithium battery charging line. The discharge MOS transistor group is composed of multiple discharge MOS transistors connected in parallel. The fast shutdown circuit includes a transistor Q17. The emitter of the transistor Q17 is connected to the gate of each discharge MOS, the base is connected to the DHC pin of chip U1, and the collector is grounded through resistor R70. A diode D3 is added between the emitter and the base to form a potential difference between the base and the emitter, ensuring that the transistor Q17 can conduct normally.

2. The fast shutdown circuit based on a lithium battery protection board according to claim 1, characterized in that, The transistor Q17 is a PNP type transistor.

3. The fast shutdown circuit based on a lithium battery protection board according to claim 2, characterized in that, The anode of diode D3 is connected to the base of transistor Q17, and the cathode of diode D3 is connected to the emitter of transistor Q17.

4. The fast shutdown circuit based on a lithium battery protection board according to claim 3, characterized in that, When the DHC pin of the protection chip U1 is working normally, it outputs a high level, at which time Q17 is in the off state.

5. The fast shutdown circuit based on a lithium battery protection board according to claim 4, characterized in that, When the DHC pin of the protection chip U1 outputs a low level, transistor Q17 is turned on. The gate current of the discharge MOSFET flows to the resistor R70 connected to the collector of transistor Q17 and is consumed, causing the gate voltage of the MOSFET to be pulled down quickly so that the discharge MOSFET is completely turned off.

6. The fast shutdown circuit based on a lithium battery protection board according to claim 5, characterized in that, The resistance R70 is adjusted according to the gate charge of the MOS: 1kΩ~10kΩ.

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