**What is a Lithium Battery Protection Board?**
A lithium battery protection board is an essential component that ensures the safe and efficient operation of a series-connected lithium battery pack. It helps maintain a balanced voltage across individual cells, keeping the voltage difference below a set threshold (typically ±20mV), which improves the overall charging performance in a series configuration. Additionally, it continuously monitors critical conditions such as overvoltage, undervoltage, overcurrent, short circuits, and high temperatures, providing necessary protection to extend the battery’s lifespan. Undervoltage protection prevents damage caused by deep discharging, ensuring each cell remains within a safe operating range.
The finished lithium battery consists of two main parts: the battery core and the protection board. The battery core includes a positive electrode, separator, negative electrode, and electrolyte, all wound or layered and sealed into a casing. Once assembled, the battery core is paired with a protection board, which plays a crucial role in safeguarding the battery from potential damage due to improper charging or discharging. While the protection board does not charge the battery, it manages current flow and provides safety features like short-circuit and overcurrent protection.
**Lithium Battery Protection Board Technical Parameters**
- **Balancing Current:** 80mA (at VCELL = 4.20V)
- **Balancing Control Point:** 4.18±0.03V
- **Overcharge Threshold:** 4.25±0.05V (optional: 4.30±0.05V)
- **Overdischarge Threshold:** 2.90±0.08V (optional: 2.40±0.05V)
- **Overdischarge Delay:** 5ms
- **Overdischarge Release:** Disconnect load when each cell voltage exceeds the overdischarge threshold
- **Overcurrent Release:** Disconnect load automatically
- **Overtemperature Protection:** Requires a recoverable temperature switch
- **Working Current:** 15A (customizable based on customer needs)
- **Static Power Consumption:** 0.5mA
- **Short-Circuit Protection:** Automatically disconnects load and recovers itself
- **Main Functions:** Overcharge, overdischarge, short circuit, overcurrent, overtemperature, and balancing protection
**Interface Definition**
The protection board has separate charging and discharging ports. Both share the same positive terminal (B+), while B- connects to the battery’s negative terminal, C- is the negative terminal for charging, and P- is the negative terminal for discharging. All pads are via-type with 3mm diameter holes. The battery charge detection interfaces are provided as DC pins.
**Detailed Analysis of the Lithium Battery Protection Board Principle**
The protection board is composed of two key components: a protection IC and a MOSFET string. The IC uses a precision comparator to monitor the battery voltage and trigger protective actions when necessary. The MOSFET acts as a fast switch in the discharge circuit, cutting off current flow when a fault is detected. Additional components like resistors, capacitors, FUSE, PTC, NTC, ID, and memory chips are also integrated into the board to enhance functionality and safety.
During charging, lithium batteries require constant current followed by constant voltage. If the charging process goes out of control, the voltage can rise beyond safe limits, risking damage or even thermal runaway. The protection board activates its overcharge protection feature, cutting off the charging circuit to prevent further voltage increase and ensure safety.
**Why Do Some Lithium Battery Protection Boards Need to Be Activated?**
Not all protection boards require activation, but some older IC-based designs do. This is primarily done to reduce static electricity and minimize energy loss during storage, allowing the battery to last longer. In these cases, the protection circuit must be activated before use to allow normal operation.
The field-effect transistors (FETs) used in the protection board act as switches. The control circuit only powers up after the FET is turned on. Therefore, if the board is not activated initially, the circuit will not function, and the battery will not provide power. To activate it, the battery must be connected to a charger, which supplies power to the control circuit, enabling the protection board to operate normally.
**How to Activate a Lithium Battery Protection Board**
If the protection board is locked due to overcurrent or overdischarge, you may need to activate it. One common method is to connect the battery to a charger, which powers the control circuit and allows the board to function. Alternatively, you can short the B- (battery negative) and P- (discharge negative) terminals. This action resets the MOSFET’s gate voltage, releasing the protection. However, avoid applying heavy loads during this process, as it may cause sparks. Most boards are designed to handle this safely, and activation typically does not damage the board.
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