Silicon Controlled Switch (SCS) terminations How many external leads (terminals) does a Silicon Controlled Switch (SCS) typically have?

Introduction / Context:
A Silicon Controlled Switch (SCS) is a four-layer, four-junction device related to the SCR but with additional control terminals. Recognizing its terminals is important in legacy trigger and control circuits.

Given Data / Assumptions:

• SCS has both anode and cathode gate controls.
• It is not as common today, but knowledge remains relevant for understanding thyristor families.

Concept / Approach:

Unlike an SCR, which has three terminals (anode, cathode, gate), an SCS typically adds a second gate terminal so that turn-on and turn-off can be controlled through gate actions at either polarity, yielding four external leads.

Step-by-Step Solution:

Verification / Alternative check:

Reference device datasheets and power electronics texts confirm the four-terminal structure and dual-gate control of SCS devices.

Why Other Options Are Wrong:

2-lead implies a diode; 3-lead corresponds to SCR/triac; 5 or 6 leads are not used for SCS in standard practice.

Common Pitfalls:

Assuming all four-layer switches have only one gate; mixing up SCS with SCR or TRIAC terminal counts.

Final Answer:

4 leads