BD139 NPN Transistor

Type: NPN (Negative-Positive-Negative) transistor: In NPN transistors like the BD139, current flows from the collector (C) to the emitter (E) when a small current is applied to the base (B).

Polarity: The BD139 is an NPN transistor, which means it amplifies or switches electronic signals with a positive voltage at the collector relative to the emitter.

Amplification: The BD139 has a moderate gain, typically ranging from 40 to 250. This makes it suitable for amplification purposes in a wide range of small and medium-sized signal applications.

Voltage Ratings: The transistor is often rated for a maximum collector-emitter voltage (VCEO) of around 80 to 80 volts and a collector current (IC) of up to 1.5 A.

Package Type: The BD139 is typically available in a TO-126 package, which is a commonly used through-hole package for easy mounting on a PCB.