What is a Power thyristors, SCR, triac thyristor, Triac circuit

 TN2540 Series 600 V 25 A SMT Silicon Controlled Rectifier - D2PAK

https://www.futureelectronics.com/p/electromechanical--circuit-protection--protection-thyristors/tn2540-600g-tr-stmicroelectronics-1324102