A device that cannot be triggered with a low voltage of either polarity is

A device that cannot be triggered with a low voltage of either polarity is

Right Answer is:

Diac

SOLUTION

A diac is a two-terminal trigger device fabricated as a gateless triac that triggers by a breakdown at a designed low voltage and is often used in the gate circuit of a thyristor or triac. The figure shows the schematic symbol for the diac. At low voltages or either polarity, a diac is completely non-conducting; however, once its breakdown threshold is reached it can conduct in either direction.

When a diac is used, the gate of the thyristor can be connected to the cathode by a low-value resistor to avoid accidental triggering. In addition, if the triggering waveform rises slowly, the diac will ensure that the thyristor is switched on by a fast-rising pulse of current, so avoiding uncertain triggering times. 

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