How to judge the quality of TVS transient suppression diode?

Comprehensive guide to judging the quality of TVS transient suppression diodes: in-depth analysis from principle to practical operation
As the core component of circuit protection, the reliability of TVS transient suppression diode directly affects the system's anti-interference ability. To determine the quality of TVS tubes, it is necessary to combine static parameters, dynamic characteristics, and failure modes, and achieve accurate evaluation through a scientific testing process.
1、 Failure Mode Analysis of TVS Tube
TVS tube failure usually manifests in the following three modes:
open failure
Phenomenon: TVS tube loses its protection function, and transient voltage directly impacts the downstream circuit.
Reason: Long term exposure to overload pulses resulted in PN junction burnout.
Testing focus: Measure whether the reverse cut-off voltage (VRMM) disappears.
Short circuit failure
Phenomenon: The TVS tube continues to conduct, causing a short circuit in the circuit.
Reason: The PN junction cannot be restored after breakdown caused by overvoltage impact.
Detection focus: Check if the forward conduction voltage (VF) drops abnormally.
Parameter drift
Phenomenon: The clamp voltage (VC) increases and the protection capability decreases.
Reason: Material performance degradation caused by high temperature or long-term stress.
Testing focus: Compare the parameters of the new device and confirm whether VC and VRMM are offset.
2、 Static parameter detection: basic screening and preliminary judgment
1. Resistance range test of multimeter (on road inspection)
Positive conductivity test:
Set the multimeter to diode mode, with the red probe connected to the anode of the TVS tube and the black probe connected to the cathode.
Normal value: Display 0.5~0.7V (silicon-based TVS) or 0.2~0.3V (Schottky TVS).
Outlier: If OL (open circuit) or close to 0V (short circuit) is displayed, it indicates that the device is damaged.
Reverse Cut off Test:
Swap the probes and measure the reverse resistance.
Normal value: displays OL (infinity).
Outlier: If a fixed resistance value is displayed, it indicates that the TVS has broken down and short circuited.
2. Precision source meter testing (offline detection)
Reverse Cut off Voltage (VRMM) Measurement:
Apply reverse voltage until the leakage current is ≤ 1 μ A, and record the voltage value.
Qualification standard: VRWM should meet the specification with a deviation of ± 5%.
Measurement of breakdown voltage (VBR):
Gradually increase the reverse voltage to a leakage current of 1mA and record the voltage value.
Qualification standard: VBR should be within ± 10% of the nominal value specified in the specification book.
3、 Dynamic characteristic testing: simulating real working conditions for verification
1. Pulse testing (validation of key parameters)
Testing equipment: Surge generator, oscilloscope.
Test steps:
Apply IEC 61000-4-5 standard pulses (such as 8/20 μ s waveform) to the TVS tube.
Record the clamp voltage (VC) and peak pulse current (IPP).
Repeat the test 3 times to confirm parameter consistency.
Qualification criteria:
VC ≤ the nominal value specified in the specification book, and the deviation of three tests is less than 5%.
IPP ≥ 80% of the nominal value specified in the specification book.
2. Junction capacitance (Cj) test
Testing equipment: LCR table.
Test conditions: frequency 1MHz, voltage 0V.
Qualification standard: Cj should comply with the specification book's nominal value with a deviation of ± 10%.
Caution: A Cj deviation of>20% in high-frequency applications may result in signal distortion.
4、 Failure localization technology: precise diagnosis of the root cause of problems
1. Open circuit failure location
Phenomenon: TVS tube has no clamping action during pulse testing.
Testing method:
Observe the temperature distribution during pulse testing using an infrared thermal imager.
The normal surface temperature of TVS tube should be ≤ 125 ℃, and there should be no temperature change when open circuit failure occurs.
2. Short circuit failure location
Phenomenon: TVS tube continues to conduct, resulting in a short circuit in the circuit.
Testing method:
Use X-ray perspective to check for internal wire breakage or virtual soldering.
Analyze the suspicious device by opening it and observe whether the PN junction is burned.
3. Parameter drift positioning
Phenomenon: TVS tube clamp voltage VC increases.
Testing method:
Use a semiconductor parameter analyzer to test the I-V curve.
Compare the curve of the new device to confirm whether the slope of the breakdown region slows down (indicating a decrease in carrier lifetime).
5、 Comprehensive judgment process and practical suggestions
Preliminary screening: Use a multimeter for on road testing to eliminate short/open circuit faults.
Parameter verification: Conduct offline precision testing on suspicious devices to confirm whether VRWM, VBR, and Cj meet the standards.
Dynamic assessment: Verify VC and IPP through pulse testing to ensure compliance with application scenario requirements.
Failure analysis: Open or X-ray inspect the failed components to locate the root cause.
Practical case:
A certain industrial power supply frequently failed during lightning strike testing, and the TVS tube clamp voltage VC was found to be too high. Through parameter analysis, it was found that the TVS tube experienced a decrease in the carrier lifetime of silicon material due to long-term high temperature, and the VC drifted to 120% of the nominal value in the specification book. After replacing with a high-temperature TVS tube (working temperature -55 ℃~+175 ℃), it passed 100 lightning strikes without failure.
6、 Summary: TVS tube reliability assurance system
Design phase:
Choose the appropriate power level based on the application scenario (such as selecting TVS with lightning protection ≥ 3000W).
Reserve a 20% parameter margin (such as selecting TVS with VRMM=15V for a circuit voltage of 12V).
Production stage:
Perform 100% pulse testing and junction capacitance screening.
Adopt multi-level protection (TVS+GDT combination) for key equipment.
Maintenance phase:
Regularly use a thermal imager to inspect the surface temperature of TVS tubes.
Perform parameter drift screening on aging equipment (once a year).
Through a systematic detection process and reliability design, the application stability of TVS tubes can be significantly improved, avoiding system failures caused by device failures.