Engineering Guide: Clamping Voltage & Power Rating in TVS Diodes

Designing a reliable surge protection stage requires more than matching breakdown voltage to the system rail. Real-world robustness depends on clamping voltage, peak pulse power capability, dynamic resistance and the diode’s behavior during IEC 61000-4-5 surge testing. This article explains the key engineering principles using SMAJ, SMBJ and SMCJ families from Kingtronics.

Why Clamping Voltage Is the True Protection Parameter

In a surge event, the TVS diode enters avalanche conduction within nanoseconds. The most important parameter is the clamping voltage VC, which is the maximum voltage the protected circuit will see at the rated peak pulse current.

If VC is too high, the load is overstressed.
If VC is too low, the diode absorbs excessive energy and overheats.

An engineering approximation is:

VC ≈ VBR + IPP × Rdynamic

where Rdynamic is the diode’s effective resistance during surge.
This is why design engineers should choose TVS diodes based on clamping behavior, not only breakdown voltage.

Browse all TVS series:
https://www.kingtronics.com/Transient-Voltage-Suppessors

Peak Pulse Power: The Main Indicator of Surge Strength

Peak Pulse Power (PPP) specifies how much energy the TVS diode can safely absorb during an 8/20 μs pulse. This value varies significantly by package.

Typical PPP levels:
SMAJ: 400 W
SMBJ: 600 W
SMCJ: 1500 W
1.5KE axial: 1500 W
P4KE axial: 400 W
SA axial: 500 W
P6KE axial: 600 W (discontinued but still used in legacy designs)

High-stress applications such as industrial control, LED drivers, EV chargers and outdoor power systems should use high-power options such as SMCJ or 1.5KE.

Datasheets:
1.5KE: https://www.kingtronics.com/pdf/1.5KE-Series.pdf
P4KE: https://www.kingtronics.com/pdf/P4KE-Series.pdf
P6KE: https://www.kingtronics.com/pdf/P6KE-Series.pdf
SA Series: https://www.kingtronics.com/pdf/SA5.0A-Series.pdf

Package Selection: SMAJ, SMBJ or SMCJ

These three SMD packages cover most industry requirements.

SMAJ Series (Most Requested)

Used in communication devices, consumer electronics, IoT, automotive electronics and small power rails.
https://www.kingtronics.com/Transient-Voltage-Suppessors/smaj-transient-voltage-suppressor

SMBJ Series (Most Requested)

A stronger option for SMPS, industrial sensors, motor drivers and general-purpose protection.
https://www.kingtronics.com/Transient-Voltage-Suppessors/smbj-transient-voltage-suppressor

SMCJ Series (Most Requested)

Chosen for heavy-surge environments: EV chargers, LED drivers, control cabinets, outdoor equipment and power conversion.
https://www.kingtronics.com/Transient-Voltage-Suppessors/smcj-transient-voltage-suppressor

Response Time and Real Surge Behavior

A well-designed TVS diode reacts within picoseconds to nanoseconds. This rapid response is essential for USB, MCU/FPGA I/O, RF modules, automotive ECUs and SELV circuits.
In IEC 61000-4-5 testing, this speed determines whether sensitive devices survive the first peak of the surge.

Reference demo video:
https://youtu.be/wq-Z1wMA6eI?si=nzUpsXHNHKkXhvjq

Practical Selection Criteria

Select a TVS diode based on the following four engineering parameters:

1. Working voltage VWM higher than maximum operating voltage
2. Breakdown voltage VBR suitable for the rail
3. Clamping voltage VC low enough to protect downstream devices
4. Peak pulse power rating sufficient for expected surge energy

For industrial, outdoor or high-power systems, SMCJ and 1.5KE provide the most reliable margin.

Conclusion

Clamping voltage and surge power capability are the core factors behind real TVS protection. By understanding dynamic resistance, package-level power limits and surge test behavior, engineers can build more durable power and signal protection in 2025 and beyond.

Explore the complete Kingtronics TVS portfolio:
https://www.kingtronics.com/Transient-Voltage-Suppessors

For technical support or sample requests, contact: info@kingtronics.com