Bidirectional conduction capability Which of the following devices can inherently conduct current in both directions between its main terminals (bilateral conduction)?

Introduction / Context:
Understanding whether a device is unilateral or bilateral is key to AC control. Some switches conduct in only one direction (like SCRs), while others are constructed to conduct in both (SBS, TRIAC).

Given Data / Assumptions:

• Focus on conduction directionality between main terminals.
• Gate/control terminals ignored for this property.

Concept / Approach:

The SBS is a symmetrical triggering device that conducts in either polarity once its breakover threshold is reached in that polarity. It is used to trigger TRIACs or for symmetrical relaxation oscillator behavior. By contrast, an SCR is unilateral, and a SUS is explicitly unilateral, while a UJT is a transistor used as a trigger/oscillator, not a bilateral power switch.

Step-by-Step Solution:

Verification / Alternative check:

Characteristic curves show symmetrical breakover in both polarities for SBS devices.

Why Other Options Are Wrong:

• SCR: conducts in forward direction only until current falls below holding value.
• SUS: “unilateral” by definition.
• UJT: a triggering device, not a bilateral power conduction element.

Common Pitfalls:

Confusing SBS with TRIAC (also bilateral); both are bilateral, but TRIAC is a higher-power AC switch while SBS is a trigger/low-power device.

Final Answer:

SBS (silicon bilateral switch)