High power semiconductor crowbar protector for AC power lines

1st March 2018
Lanna Cooper


AC power line disturbances are the cause of many equipment failures. The damage can be as elusive as occasional data loss or as dramatic as the destruction of a power supply, LED lightings, industrial system and consumer equipment such as ovens or refrigerators and television sets.

Power line disturbances go by many names - transients, surges, spikes, glitches, etc. But regardless of the specific name, an understanding of their characteristics and the operation of the various protection components available is necessary to design an effective protection circuit.

There are some popular protection components for these power input lines. The most common over voltage protection components are MOVs (Metal Oxide Varistor), high power TVS (Transient Voltage Suppression) Diodes and GDTs (Gas Discharge Tube).

In this article, we are going to discuss a new and innovative method of using a silicon crowbar compoent known as, the SIDACtor Protection Thyristor component, for the main over voltage protection solution for AC power lines.

Surge protection
Surge protection components can be divided into two basic types: Crowbar type devices such as GDTs and protection thyristor type SIDACtor components and clamp type components such as TVS diodes, MOVs etc.

The clamp type components have faster response time but are limited in their current handling ability because the transient energy must be dissipated by the clamping component. Also, the voltage drop across a clamp type component increases as a function of the conducted current passing through it.

Thus a higher clamping voltage threshold component will have a lower peak current capability. (The power rating remains the same for all components in a particular series but since power is the product of the voltage and current, an increasing voltage demands a decrease of current).

A crowbar type component can handle much higher surge current because during their on-state condition, the voltage across the component is extremely low. These crowbarring components act as a 'near short circuit value' path shunting the transient energy away from the protected equipment. And this, low on-state voltage will further reduce any electrical over stress to the protected circuit.

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