The BT139-800.127 800V, 4A Thyristor from NXP is a TRIAC (three terminal switch) which is designed for use in a wide range of AC switching applications. It has an 800V, 4A Vdrm, Vrrm and can handle an On-state RMS current of up to 8 Arms, making it suitable for heavy duty switching. It is also RoHS compliant, making it ideal for use in many industrial environments.