Will the Fuse Blow if a TVS Diode Fails?

Date:2025-05-12 Categories:Product knowledge Hits:510 From:Guangdong Youfeng Microelectronics Co., Ltd


1. TVS Diode Failure Modes

TVS diodes can fail in three primary ways:


  • Short Circuit: This is the most common failure mode. A shorted TVS diode creates a low-resistance path to ground, causing excessive current flow. In this scenario, the fuse should blow to prevent damage to the circuit.

  • Open Circuit: A less common failure, an open TVS diode no longer conducts current. Since no abnormal current is drawn, the fuse will not blow, leaving the circuit unprotected against future surges.

  • Degradation: The TVS diode’s performance deteriorates over time, such as increased leakage current. This may not trigger the fuse immediately but can lead to long-term issues like battery drain in battery-powered systems.

2. Fuse Protection Mechanism

Fuses are designed to interrupt current flow when excessive heat (caused by overcurrent) melts the fuse element. For a fuse to blow, the current must exceed its rated current for a sufficient duration. The key parameter here is I²t (current squared multiplied by time), which quantifies the energy required to melt the fuse.

3. Key Factors Influencing Fuse Blow

a. TVS Failure Mode

  • Short Circuit: A shorted TVS diode diverts high current to ground, exceeding the fuse’s I²t rating. The fuse will blow if the energy (I²t) from the short circuit exceeds the fuse’s melting energy.

  • Open Circuit: No overcurrent occurs, so the fuse remains intact.

b. Fuse and TVS Coordination

Proper selection of fuse and TVS is critical. The TVS must handle transient surges within its peak pulse power rating, while the fuse must clear faults before the TVS fails. For example:


  • A TVS with a 600W peak power rating (e.g., Littelfuse SMBJ24A) paired with a 1A slow-blow fuse may not protect against a 200V input fault if the fuse’s voltage rating is insufficient.

  • Fast-acting fuses are preferred for semiconductor protection, as they clear faults before the TVS reaches its thermal limits.

c. Environmental Conditions

Factors like temperature and fuse placement affect performance. A fuse operating at high temperatures may blow faster, while a poorly placed fuse (e.g., in a high-heat area) may degrade over time.

4. YFW’s Approach to Reliability

At YFW, we prioritize robust TVS diode designs to minimize failure risks. Our TVS diodes, such as the SMBJ series, are engineered with:


  • High-energy absorption capability to handle surges effectively.

  • Low clamping voltage to protect downstream components.

  • Avalanche breakdown technology for predictable failure modes.


For optimal protection, we recommend:


  1. Fuse-TVS Coordination: Match the fuse’s I²t rating to the TVS’s peak pulse current.

  2. Regular Testing: Monitor TVS performance to detect degradation early.

  3. Design Redundancy: Use multiple TVS diodes or fuses in critical applications.

Conclusion

The fuse will not always blow when a TVS diode fails. If the TVS fails short, the fuse should blow to protect the circuit. However, an open-circuit failure or gradual degradation may leave the fuse intact, compromising system safety. To ensure reliable protection, engineers must carefully select and coordinate TVS diodes and fuses, considering their ratings, failure modes, and environmental conditions.


For cutting-edge TVS solutions that prioritize safety and performance, explore YFW’s TVS diode portfolio.


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