Core Functions and Working Principle

A TVS (Transient Voltage Suppressor) diode is a critical protection component in a Battery Management System (BMS). Its primary function is transient voltage suppression.

When sudden high-voltage pulses occur in the circuit—caused by either external or internal factors (see below)—the TVS diode can switch from a high-impedance state to a low-impedance state within nanoseconds. It diverts excess current to ground and clamps the voltage at a safe level, effectively protecting sensitive electronic components.

Protected components in a BMS typically include:

• Main control MCU and AFE chips

• Communication interface ICs (such as CAN or RS485 transceivers)

• ADC input ports of voltage and current sampling circuits

Operating states of a TVS diode:

• Normal operation: High impedance, extremely low leakage current, no impact on the circuit

• Abnormal conditions: Rapid response when the voltage exceeds the breakdown threshold—much faster than MOVs (metal oxide varistors) or gas discharge tubes (GDTs)

Typical TVS Diode Applications in a BMS

In a lithium battery BMS, TVS diodes are mainly deployed at key “entry points” that are highly susceptible to surge and transient disturbances:

1. Battery Voltage Sensing Lines

• Location: Between battery cells and the BMS monitoring (AFE) chip

• Risk: Long wiring may introduce induced voltage spikes, especially during motor or contactor switching

• Function: Protects AFE analog input pins from overvoltage damage

2. Communication and External Interfaces

• Location: CAN bus, RS485, UART, and other communication lines

• Risk: Long cables are prone to electromagnetic interference (EMI) and electrostatic discharge (ESD)

• Function: Protects communication transceivers and ensures stable data transmission

3. External Power Supply Inputs

• Location: 12V / 24V auxiliary power input of the BMS

• Risk: Load dump events in automotive or industrial environments can generate extremely high voltage spikes

• Function: Stabilizes the input voltage and protects downstream DC-DC converters and the MCU

4. Relay / Contactor Drive Coils

• Location: Connected in parallel across the main relay or pre-charge relay coils controlled by the BMS

• Risk: High reverse electromotive force (EMF) generated when the coil is switched off

• Function: Absorbs the induced voltage spike and protects internal driver transistors or MOSFETs

Major Threats Addressed by TVS Diodes

TVS diodes are designed to counteract three common electrical threats:

How to Select the Right TVS Diode for a BMS (Key Parameters)

Proper TVS selection is essential to effective protection. The following parameters must be carefully matched to the protected circuit:

• Reverse Stand-off Voltage (Vr):
  The maximum voltage the TVS diode can withstand during normal operation. It must be higher than the maximum normal operating voltage of the line (e.g., 15V or 18V TVS for a 12V system).

• Clamping Voltage (Vc):
  The maximum voltage across the TVS during a surge event. This value must be lower than the absolute maximum voltage rating of the protected IC pins—this is the key to effective protection.

• Peak Pulse Power:
  The maximum transient power the TVS diode can absorb (e.g., 600W, 1500W), selected based on expected surge energy levels.

• Junction Capacitance:
  Especially critical for data and communication lines such as CAN. High-speed signals require low-capacitance TVS diodes (typically <50 pF, and even <3 pF for high-speed applications) to avoid signal distortion.

Conclusion

In a lithium battery BMS, the TVS diode is a true “behind-the-scenes bodyguard.”
Under normal conditions, it remains unnoticed. But the moment a voltage spike appears, it reacts instantly, absorbing dangerous energy and safeguarding critical electronics.

TVS diodes are a key protection component that ensures long-term BMS stability and reliability in complex electromagnetic environments—preventing unexpected failures and costly damage.