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BD139 Transistor

BD139 is an NPN electronic transistor. This post discusses the pinout configuration, features, and datasheet of the BD139 transistor.

BD139 transistor pinout, features, and specifications

BD139 Pinout Configuration

Pin NumberPin NameDescription
1EmitterEmitter pin is normally connected to the ground. Is where the current output of the transistor
2CollectorCollector pin is normally connected to the load. Current flow in through the collector pin.
3BaseThe base pin is used in biasing the transistor. It controls the switching ON or OFF in the transistor

Technical Specifications & Features of BD139 Transistor.

Package TypeTO-126
Transistor TypeNPN
Max. Collector Current (Ic)1.5A
Max. Collector-Emitter Voltage (Vce)80V
Max. Collector -Base Voltage (Vcb)80V
Max.Emitter-Base Voltage (Vebo)5V
Max. Collector dissipation (Pc)12.5Watts
Max. Transition Frequency (fT)190 MHz
Mini. & Max. Dc current Gain (hfe)25 – 260
Mini. & Max storage and Operation Temperature.-55 to +150 ccentigrade

BD139 Equivalent Transistor.

BD230, BD349, BD379, BD140

PNP Complementary of BD139 Transistor.

BD140 is the PNP complimentary of BD139.

Description & Explanation of BD139 Transistor.

BD139 is an NPN transistor used for switching, amplifying, and other general functions.

The Base acts as a switch between the collector and the emitter. When the base of the transistor is biased it makes the collector and emitter pin to be in a close state (ON) making it possible for signal to flow through the collector and emitter.

The gain of BC139 transistor ranges from a minimum of 25 to a maximum of 260. Transistor gain determines its amplification. But for the case of BC139, a maximum of 1.5A is what can be passed through the collector. Current above 1.5A in the collector will damage the transistor.

To bias the transistor, a small current (Base Current), of around 1/10th of the collector current is fed at the Base of the transistor. The small base current Is what triggers the switch of the transistor and puts it in a close (ON)state. When the base current is removed from the transistor, the collector to emitter becomes Open (OFF). The maximum Collector-to-emitter voltage of the transistor is 80V thus loading more than 80V will end up damaging the transistor.

Where to use BD139 & how to use it.

The transistor can be used for commercial and electronic student projects. It can be used in analogy electronic project microcontroller circuits such as Arduino projects.

The transistor can drive a load of 1.5A but when used in driving a load above 1.5A, a suitable heat sink should be used with the transistor to cool the dissipated heats

It can also be used to switch and control electronic equipment like LEDs, DC motors, and relays that operate below 1.5A.


  • Switching of loads under 1.5A
  • Signal amplifiers
  • Used in building DC power supply
  • DC motor driver
  • Darlington pair

How to safely operate BD139 transistor.

Adhere to the following instructions when using a BD139 transistor.

  • Do not operate the transistor with a voltage above 80V.
  • The transistor shouldn’t be used to drive a load that drives more than 1.5A.
  • Always use a suitable base resistor to limit the base current of the transistor to its appropriate biasing current.
  • Always use a heat sink on the transistor to cool the dissipated heat.
  • The transistor should be operated or stored at a temperature between the range of -55 to +150 centigrade.

BD139 Datasheet

Copy and paste the link below to your browser to download the datasheet of the transistor. Other features and specifications that weren’t covered in this post can be found on the transistor datasheet.

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