Thyristor surge suppressor (TSS)

What is a Thyristor Surge Suppressor or crowbar protection component?

When protecting parallel (double) circuit transmission lines, devices have two main functions in transient mode: clipping the voltage and drifting the current due to overload.

If the first function is perfectly filled using an avalanche diode which confirms the success of the TVS, the second is limited by the permanent presence of the voltage at the diode's terminals. The use of increasingly sophisticated electronic components is also increasingly fragile and the publication of new standards no longer allows the use of diodes in certain applications.

To solve this issue, designers use semiconductor devices having two conduction states such as a thyristor (or triac in the bidirectional version).


By switching from a blocked state (at rest) to a passing state with low voltage drop (speed transient overload) Thyristor Surge Suppressors, a semiconductor component, makes it possible to protect circuits against high overload currents and protect the circuit terminals from any risk of overvoltage.

A Thyristor Surge Suppressor (TSS) prevents overvoltages or power surges from damaging power supplies. When a Transient Voltage Suppressor (TVS) is not strong enough to ensure compliance with high surge criteria defined in ITU-T K series, GR-1089 and TIA-968-A requirements, a TSS, or Trisil™, in a crowbar protection topology is recommended.

Designed to protect new high-voltage digital line cards as well as classical subscriber line interface cards (SLIC) against transient overvoltages, these components present a very low gate triggering current (IGT) in order to reduce the current consumption on printed circuit board during the firing phase. 

Advantages of thyristor surge protection devices (TSPDs)

Like a TVS in normal operation, the TSS is transparent for the application but then acts a short circuit during surges.

TSS brings many advantages over traditional Gas Discharge Tube (GDT) surge arrestors including stability over time (no ageing phenomenon) and turn-on without parasitic oscillation or ringing.

TSS are designed for telecom network applications such as xDSL, T1/E1, Ethernet, EPON, and GPON applications and voice band protection in line cards and telephony equipment in both infrastructure and residential installations.