This part is a kind of semiconductor called BT151-800RG.

Function of this product has SCRs.

Manufacturers : First Semiconductor

Image and pinout :

Some of the text within the PDF file :

BT151(500R-650R-800R)G SCRs Description Standard gate triggering SCR is fully isolated package suitable for the application where requiring high bidirectional blocking voltage capability and also suitable for over voltage protection, motor control circuit in power tool, inrush current limit circuit and heating control system. Simplified outline TO-220AB 123 Features • Blocking voltage to 800 V • On-state RMS current to 12 A • Ultra low gate trigger current Symbol ak g Applications • Motor control • Industrial and domestic lighting • Heating • Static switching Pin 1 2 3 TAB Description cathode anode gate anode SYMBOL PARAMETER VDRM VRRM Repetitive peak off-state voltages Voltages 500RG 650RG 800RG IT RMS RMS on-state current ITSM Non-repetitive peak on-state curr [ ... ]

BT151-800RG PDF Datasheet Download