Thyristors and Tranducers - Technical MCQs

Q1:

A TRIAC:

A can trigger only on positive gate voltages

B can trigger only on negative gate voltages

C cannot be triggered with gate voltages

D can be triggered by either a positive or a negative gate voltage

ANS:D - can be triggered by either a positive or a negative gate voltage

The triac is a three-terminal ac switch that is triggered into conduction when a low-energy signal is applied to its gate terminal. Unlike the SCR, the triac conducts in either direction when turned on. The triac also differs from the SCR in that either a positive or negative gate signal triggers it into conduction. Thus the triac is a three terminal, four layer bidirectional semiconductor device that controls ac power whereas an SCR controls dc power or forward biased half cycles of ac in a load.