How to judge the quality of TVS transient suppression diode?

To determine the quality of TVS (transient suppression diode), comprehensive testing should be conducted based on its electrical characteristics and physical state. The following is a systematic testing method and logical analysis:
1、 Appearance inspection
Physical integrity
Observe whether there are signs of burning, cracking, bulging, or corrosion on the pins of the tube body. If such a phenomenon exists, it may be due to overvoltage breakdown or aging failure.
Check if the packaging is intact, especially for glass passivated TVS, and confirm that there are no cracks that may expose the internal chips.
Clarity of identification
Confirm that the model and polarity markings (if any) are clear and distinguishable. Vague or missing identification may imply that the product source is unreliable or damaged.
2、 Electrical parameter testing
1. Static parameter detection (when not powered on)
Forward/reverse resistance measurement (using multimeter diode mode):
Forward conduction voltage: TVS should exhibit a high resistance state (similar to the forward voltage drop of a regular diode, about 0.7V) before breakdown. If the forward resistance is too low (such as approaching a short circuit), it may indicate an internal short circuit.
Reverse leakage current: When reverse biased, the resistance should be extremely high (>1M Ω). If a low resistance value (such as a few k Ω) is displayed, it indicates abnormal leakage current and may have deteriorated.
2. Breakdown voltage test (dynamic characteristics)
Using specialized equipment (such as LCR meter or voltage tester):
Breakdown voltage (VBR): Apply a slowly rising voltage until the TVS conducts, and record the voltage value at the moment of conduction. Compare with the nominal value (with a tolerance of ± 10% deviation). If VBR is significantly lower than the nominal value, it indicates that the device has deteriorated.
Clamp voltage (VC): Measure the voltage across the TVS under surge current. If VC is much higher than the specification value, it indicates a decrease in clamping ability.
3. Leakage current test
Apply a voltage near the reverse breakdown voltage (such as 80% of VBR) and measure the leakage current. The normal value should be less than the specifications (such as<5 μ A). Excessive leakage current indicates performance degradation.
3、 Functional verification testing
Surge simulation test
Apply a typical surge current (such as an 8/20 μ s waveform) using a surge generator and observe whether the TVS can effectively clamp the voltage without any signs of damage. If the device heats up severely or fails, it needs to be replaced.
Continuous high voltage test
Apply a DC voltage slightly higher than VBR (such as 1.1 × VBR) and monitor leakage current and temperature rise for a long time. Abnormal temperature rise or breakdown indicates insufficient voltage resistance.
4、 Auxiliary judgment method
Comparison method: If there are multiple TVS of the same model, their electrical parameters (such as VBR and leakage current) can be compared, and those with significant differences are suspicious.
Alternative method: Replace the suspected faulty component with a known good TVS and observe whether the circuit returns to normal operation.
5、 Precautions
Testing safety: High voltage testing requires the use of professional equipment to avoid human contact.
Parameter matching: The VBR, VC, and power levels of different models of TVS vary greatly, and strict reference to the specifications is required.
Environmental factors: High temperature or humid environments may accelerate TVS aging, and actual usage conditions should be considered during testing.
summary
The judgment of TVS quality requires multidimensional verification: appearance without damage is the foundation, static resistance and dynamic breakdown voltage are the core indicators, and functional testing verifies actual performance. The comprehensive results can accurately evaluate its reliability and avoid misjudgment leading to circuit protection failure.