The BT139-800G,127 is a silicon controlled rectifier (SCR) manufactured by NXP Semiconductors. It is a 3-pin device designed to switch high current applications with low signal control. It has an on-state output current of 800 Amps, a repetitive peak off-state voltage of 800V and a non-repetitive peak off-state surge current of 12kA. This device can be used for heavy-duty switching applications such as motor control, power supplies, welding equipment, and solar inverters. It is RoHS compliant and can operate at temperatures ranging from -55°C to 125°C.