In the context of modern electronic devices becoming more precise and the working environment becoming more complex, the issue of circuit safety, especially the protection against lightning strikes and transient overvoltage (Surge), has become an important aspect that cannot be ignored in product design. Among them, TVS (Transient Voltage Suppressor) and TSS (Thyristor Surge Suppressor) are two widely used surge protection devices. Although both serve the same goal - to protect circuits from lightning strikes or other sudden high-energy pulses - in the process of achieving this goal, they exhibit completely different physical mechanisms, performance characteristics and application boundaries.

The two guardians in the field of electronic protection: TVS and TSS

Although both are used for parallel protection, their "fighting styles are completely different". This article will be from a professional perspective, systematically analyze the working principles, electrical characteristics, typical application scenarios and selection strategies of TVS and TSS, helping engineers make scientific and reasonable choices under different system requirements.

A.   Logic of parallel protection: Handling sudden high current surges

In the parallel protection topology, the protection devices must respond promptly before the overvoltage source damages the sensitive load. TVS and TSS are specifically designed for this purpose, using the "clamping" and "switching" philosophies respectively to achieve the goal.

Parallel protection is an efficient solution for dealing with short-term, high-current surges (Surge), and its core lies in "fast response + energy diversion".

B.   Comparison Bof Two Schemes: Clamping Mechanism vs. Switching Mechanism

Option A: TVS (clamp-type device) firmly "clamps dow.n"

l  Working principle: TVS is a clamp-type protection device based on the PN junction of semiconductors. When the applied voltage reaches its breakdown voltage, TVS rapidly conducts, clamping the voltage to a safe level and preventing damage to the subsequent circuit.

l  Response time: Extremely short, usually in nanoseconds or even picoseconds.

l  Directionality: It can be divided into two types: unidirectional and bidirectional.

l  Typical product: SMBJ series (bidirectional TVS).

Option B: TSS (Switching Device) - The "Switcher" with Ultra-Fast Speed

l  Working principle: TSS is essentially a thyristor structure. When the voltage exceeds its trigger voltage VBO, TSS rapidly conducts, creating a short-circuit state, and quickly discharges the surge current.

l  Response time: Slightly slower than TVS, but still within the nanosecond range.

l  Automatic reset: Once the surge ends, TSS will automatically return to the high-resistance state.

l  Typical product: TSS series: PxxxxS (A/B/C/D) series

C、Direct comparison: Motion curves and electrical behavior

Surge Waveform

TVS's operation: Current flows only during the clamp stage. There is always a voltage (VcL) across the device's terminals, resulting in high instantaneous power and generating heat.

TSS’s operation: When the voltage reaches VBo, 'ignition' (Fires) occurs. During conduction, the voltage across the two ends is extremely low, and the self-power consumption is very small, enabling it to withstand greater surge currents.

D、Power and Efficiency: Why TSS Is More "Resistant"?

■TVS: (SMBJ) ， TSS: PxxxxS(A/B/C/D)

Same packaging, different capabilities

TVS (such as SMBJ): The current-carrying capacity significantly decreases as the breakdown voltage (VBR) increases. The higher the voltage, the smaller the current it can withstand. The maximum current-carrying capacity of SMBJ5.0CA is 10x1000 µs 60A.

TSS: Regardless of the voltage level, the current-carrying capacity remains constant. For example, the PxxxxSC series is all 10x1000 µs 100A, and the PxxxxSD series is all 10x1000 µs 200A.

Conclusion: In high-voltage and high-current applications, Leiditech TSS has a higher power density. The naming and parameters of Shanghai Leiditech TSS are as follows:

E、Selection strategy: Which option is suitable for you?

TVS and TSS each have their own advantages. TVS is known for its precise clamping, while TSS is renowned for its strong absorption. In modern electronic systems, a single protection mechanism often fails to cope with complex surge environments. Therefore, engineers should abandon the "either-or" mindset and instead construct a "TVS + TSS" collaborative protection system to achieve multi-level protection from the macroscopic to the microscopic.

F、Typical Application and Circuit Design of TSS

Semiconductor discharge tubes TSS are widely used in the protection of communication lines of electronic products in fields such as communication, security, and industry.

l  RS232/RS422/RS485 interface

l  XDSL and ISDN, HDSL transmission equipment

l  User front-end devices, such as telephones, fax machines, and modems

l  T1/E1 interface

l  Instrumentation, its distribution frames, Ethernet, and CATV equipment

l  Security products, remote monitoring, remote meter reading, and other products

6.1、RS422 RS485 Electrostatic surge protection solution

Application: Communication lines for industrial sensors, frequency converters, and instruments, susceptible to induced surges and static interference. The communication rate is typically 115200bps - 1Mbps.

Solution advantages: Surge protection for RS422 and RS485 interfaces, using low residual voltage TSS, effectively protecting RS422 and RS485 transceivers. The TSS response time is at the ns level, providing both surge protection and static protection, while ensuring signal integrity.

Meets IEC61000-4-2, static level 4, contact discharge 15kV, air discharge 8kV; IEC61000-4-5 surge 10/700μs, 6KV. Refer to the detailed specification sheet for Leiditech WeChat Mini-Program 18.5. Additionally, using P0080SD can handle surges of 8/20μS 2KV.

6.2、CAN bus electrostatic surge protection

Solution Advantage: Surge protection for CAN interface, using TSS with low residual voltage, effectively protecting the interface. The TSS response time is at the ns level, which can prevent both surges and static electricity, and ensure signal integrity.

Meets IEC61000-4-2, static level 4, contact discharge 15kV, air discharge 8kV; IEC61000-4-5 surge 10/700μs, 8KV. Refer to the detailed specification sheet for the Leiditech WeChat Mini-Program 16.4.