Will a Protected Circuit’s Normal Operating Voltage Above the TVS Diode’s Breakdown Voltage Damage the TVS?

Date:2025-05-08 Categories:Product knowledge Hits:508 From:Guangdong Youfeng Microelectronics Co., Ltd


Understanding TVS Diode Fundamentals

A TVS (Transient Voltage Suppressor) diode is a semiconductor device designed to protect circuits from voltage spikes and electrostatic discharge (ESD). It operates based on the avalanche breakdown principle, where it remains in a high-impedance state under normal conditions. When a transient voltage exceeds its VBR, the TVS rapidly switches to a low-impedance state, diverting excess current to ground and clamping the voltage at a safe level .


Key parameters include:


  • VRWM (Maximum Reverse Working Voltage): The highest continuous voltage the TVS can withstand without conducting.

  • VBR (Breakdown Voltage): The threshold voltage at which the TVS enters breakdown mode (typically defined at 1 mA or 10 mA test current) .

  • IPP (Peak Pulse Current): The maximum transient current the TVS can handle before failure.

  • VC (Clamping Voltage): The voltage level the TVS maintains during avalanche breakdown.

Impact of Operating Voltage Above VBR

1. When Voltage Exceeds VRWM but Not VBR

If the circuit’s normal operating voltage exceeds VRWM but remains below VBR, the TVS may exhibit increased leakage current (IR). For example, a TVS with VRWM = 10 V and VBR = 11.1 V may conduct a few microamps at 10.5 V. While this does not immediately damage the TVS, elevated leakage can disrupt low-power or analog circuits (e.g., 4–20 mA sensors) .

2. When Voltage Exceeds VBR

When the operating voltage surpasses VBR, the TVS enters avalanche breakdown. Here’s what happens:


  • Current Surge: The TVS conducts significant current, proportional to the voltage excess. For instance, a TVS with VBR = 11.1 V may carry 10–100 mA at 11.2 V.

  • Power Dissipation: Power (P = V × I) increases rapidly. If the TVS cannot dissipate this power (e.g., due to inadequate thermal management), it may overheat and fail .

  • Long-Term Effects: Prolonged operation above VBR accelerates material degradation, reducing the TVS’s lifespan and reliability .


Critical Consideration: Damage depends on how much voltage exceeds VBR and the duration of exposure. A slight voltage overshoot (e.g., 11.2 V vs. VBR = 11.1 V) may not cause immediate harm, but sustained operation at higher voltages (e.g., 15 V) will likely lead to thermal runaway .

Mitigation Strategies

1. Proper TVS Selection

  • VRWM > Circuit’s Maximum Operating Voltage: Ensure VRWM is at least 10–20% higher than the normal voltage to avoid leakage issues.

  • VBR > Transient Voltage Threshold: VBR should be lower than the minimum destructive voltage of the protected components.

  • Power Handling: Calculate the TVS’s peak pulse power (P = VC × IPP) to ensure it matches the expected surge energy .

2. Thermal Management

  • Use heat sinks or thermal vias to dissipate heat generated during breakdown.

  • Avoid prolonged exposure to voltages above VBR .

3. Redundancy and Fusing

  • Pair the TVS with a fuse or PPTC (polymeric positive temperature coefficient) device to disconnect the circuit if the TVS fails short .

Conclusion

A TVS diode will not necessarily fail if the circuit’s normal operating voltage slightly exceeds its VBR, provided the current and power remain within the device’s limits. However, sustained operation above VBR increases the risk of thermal damage and premature failure. Engineers must prioritize TVS 选型 based on VRWM, VBR, and power handling capabilities, while implementing thermal and redundancy measures to ensure robust protection. For high-reliability applications, consult YFW’s TVS diode datasheets (e.g., YFW TVS Series) for precise parameters and application guidance.


By integrating these principles, designers can optimize TVS performance and safeguard critical electronics from voltage-related risks.


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