It seems there might be a misunderstanding. Shockley diodes are not a separate component used in thyristor and SCR (Silicon-Controlled Rectifier) circuits. Instead, Shockley diodes are the theoretical building blocks or conceptual elements from which thyristors and SCRs are constructed.
A thyristor is a semiconductor device that acts as a switch, capable of controlling the flow of electric current. It has three terminals: anode, cathode, and gate. The thyristor consists of two back-to-back Shockley diodes (PNP and NPN) connected in series, and it is also known as a "four-layer diode" or "PNPN diode." When a voltage is applied to the gate terminal, the thyristor switches from a high-resistance state (OFF state) to a low-resistance state (ON state), allowing current to flow from the anode to the cathode.
Similarly, the Silicon-Controlled Rectifier (SCR) is a specific type of thyristor that acts as a rectifier, converting alternating current (AC) into direct current (DC). It also consists of three layers (PNP) and a gate terminal. When a voltage is applied to the gate, the SCR becomes conductive, and current flows through the device until the current falls below a minimum value (holding current) or the voltage is reversed.
In summary, Shockley diodes are not separate elements used in these circuits; they are theoretical components that help explain the operation and construction of thyristors and SCRs. These devices are essential for various applications, including motor control, power regulation, and voltage regulation in electronic circuits.