Which device acts as two SCRs connected back to back but facing in opposite directions?

The TRIAC is a semiconductor device that effectively operates as two silicon-controlled rectifiers (SCRs) placed back-to-back, with their gates connected. This design allows the TRIAC to conduct current in both directions, making it useful for alternating current (AC) applications. When a TRIAC is triggered by a gate signal, it can switch on and remain on until the current flowing through it falls below a certain threshold, at which point it turns off.

This functionality allows the TRIAC to control the power flow in AC circuits, making it ideal for applications such as dimmers, motor speed controls, and light switches. The ability to control current in both directions enables it to be more versatile than a single-direction SCR, which only controls current flowing in one direction.

The other devices listed serve different purposes and do not have the same bidirectional control capabilities as a TRIAC. For instance, a DIAC is more of a switching device that remains off until the voltage exceeds a certain level and then turns on, while a phototransistor is designed to control current based on light exposure. A half-bridge inverter is a configuration used in electronic circuits to convert DC to AC but does not have the same characteristics as a TRIAC in terms of bidirectional