BD439 is a general-purpose, NPN, silicon transistor manufactured by Continental Device India Ltd. It is commonly used in various applications such as audio amplifiers, IF amplifiers, switch circuits, and oscillator circuits. It features a collector-emitter voltage of up to 80V, a collector-base voltage of up to 80V, an emitter-base voltage of 5V, and a collector current of up to 1A. It is also designed for low noise applications, and has a low ESR rate and wide operating temperature range.