BD139 NPN Transistor : Pin Configuration & Its Applications

The transistor is one kind of three-terminal semiconductor device which is available in two types like BJT and MOSFET. As compared to MOSFETs, BJT characteristics are less complex. BJTs & MOSFETs include three terminals like base, emitter & collector whereas MOSFET includes Gate, Source & Drain. There are different types of BJTs and MOSFETs are available in the market which are manufactured by different companies. From them, the BD139 transistor is one kind of NPN transistor. This article discusses an overview of BD139 NPN transistor, pin configuration, and its applications.

What is BD139 NPN Transistor?

A Bipolar NPN transistor like BD139 is available in the SOT-32 plastic package. This kind of transistor is used in different electronic circuits because of less cost and high collector current. This transistor can drive upto 1.5A loads like motors, high power LEDs, relays, etc.

BD139 NPN Transistor
BD139 NPN Transistor

The VCE (collector-emitter) & VCB (collector-base) voltage is also extremely high thus it can simply use in an electronic circuit. The dissipation current of the collector terminal is 12.5W which is ideal to utilize in audio amplifier circuits. This transistor’s saturation voltage is simply 0.5V.

BD139 NPN Transistor Working

Once the current is applied at the base terminal of this transistor, then this transistor will work in forwarding bias. This current must be above as compared to its collector current. So at the base-emitter pin, we have to provide 5V.

When this transistor is working in forward biased condition, the maximum current drawn by emitter and collector terminals are 1.5A. If 1.5A of maximum current is supplying throughout this transistor then this transistor will be in Saturation Region.

Generally, we can provide a maximum of 80V across two terminals like emitter and collector. Once we detach the current supply at the base terminal of this transistor, then it will turn off, so this situation is known as the cut-off region.


This transistor is available in a plastic package but the medium power transistor is available in the metal package. This package will reduce its cost, it is not conductive & it will not be affected through other circuits. Because of this simple feature, this transistor is used mostly in amplifier applications.

This transistor is the best choice if you are looking for a transistor with medium power in a plastic package. BD139 transistor was manufactured by Phillips for specific audio applications at 160 MHZ, but it was cloned by different manufacturers like ST, Samsung, etc.

Pin Configuration

The pin configuration of the BD139 NPN Transistor is shown below. This transistor includes three pins which are discussed below.

BD139 Transistor Pin Configuration
BD139 Transistor Pin Configuration
  • Pin1 (Emitter): An emitter terminal is connected to the GND terminal and this terminal drains out the current.
  • Pin2 (Collector): This is connected normally to load where the current supplies throughout this terminal.
  • Pin3 (Base): The base terminal controls the transistor biasing; it is used to switch ON/OFF the transistor.

Features & Specifications

The main features and specifications of the BD139 transistor include the following.

  • The available package is To-225
  • It is mounted in a plastic case.
  • The Collector current (IC) of this transistor is 1.5A.
  • The collector Base voltage (VCB) of this transistor is 80V
  • Breakdown voltage from emitter to base (VBE) is 5V.
  • DC gain of this transistor (hfe) is 40 – 160
  • Breakdown voltage from emitter to base (VBE) is 5V
  • Its collector dissipation factor is 12.5w.
  • The range of junction temperature for operating & storage ranges from -55 to +150°C
  • This transistor is also accessible within PB-Free packages.

Complementary BD139 transistor is BD140 whereas equivalent BD139 transistors are BD230, BD349, BD379, BD139G, BD179, BD169, BD230, BD237G, BD237, BD379, BD791, BD789, MJE242, MJE722/ MJE244 and 2SC5171S.

How to use BD139 Transistor/Circuit Diagram?

The circuit diagram of a 12Volts to 3Volts converter with a BD139 transistor is shown below. This is also known as DC to DC converter which is used by beginners of electronics in electronic projects.

The required components of this DC to DC converter circuit mainly include BD139 NPN transistor, 1000uF & 100uF capacitors, 12V DC, Zener Diode (3.6V/0.5W), Resistor (510 Ohms), Breadboard, connecting wires & Battery clips.

DC to DC Converter Circuit using BD139 Transistor
DC to DC Converter Circuit using BD139 Transistor

This type of converter provides a cheap, easy way to design a project. As a result, this simple 12V to 3V converter circuit is designed with a BD139 NPN Transistor & Zener diode.

The gain value of this transistor ranges from 40 to 160 which determines the amplification capacity for the transistor. The highest amount of current that could supply throughout the collector pin is 1.5A, thus we cannot fix loads that use above 1.5A with this transistor.

This transistor can be biased by supplying to the base terminal that must be restricted to 1/10th of the current at the collector terminal & the maximum voltage supply across the BE pin must be 5V.

By using this converter, we can obtain a stable & smooth 3V DC o/p. This circuit uses a Zener diode with 3.6V/0.5W like a voltage regulator. At the input 12V, DC is used where this input supplies throughout C1=1000uF smoothing capacitor to get rid of any leftover noise. After that, the DC signal goes throughout a Zener diode & generates a regulated 3Volts.

Here, the BD139 NPN transistor enhances the o/p current of this converter circuit to operate high current devices. We can also change 12V – 3V through a Zener diode & a resistor however it will not supply huge current. The 3V DC signal supplies throughout the ‘C3 = 100uF’ smoothing capacitor, before supplying to the output.

This DC to DC converter circuit is used in DVD players, portable chargers and to increase/decrease DC voltage in different applications. It is also used in power industries for the load matching process.

How to Long Run BD139 Transistor in a Circuit Safely?

To run this BD139 transistor in your circuit very safely, this transistor should not be operated above 80V, do not drive load above 1500mA/1.5A & utilize an appropriate heat sink through the transistor.
The required base current can be provided by using an appropriate base resistor. This transistor’s maximum & minimum operating temperature ranges from -55 to +150 C so do not use it in the >+150 centigrade < -55 centigrade temperatures.

Where to use BD139 Transistor/Applications

The applications of the BD139 transistor include the following.

  • BD139 transistor is mainly used in beginner electronics projects in the educational field like in Arduino projects, microcontroller projects, etc.
  • This transistor drives different loads upto 1500mA so we can drive & control different electronic equipment by using it.
  • This transistor can also be used in commercial electronics. When the load is driving above 200mA then the transistor will dissolve heat so a suitable heat sink is required.
  • This transistor is used in different applications like audio amplifiers, battery chargers, power supplies, motor drivers, under 1.5A of switching loads, Darlington pair, etc.
  • It is used like RF amplifier, in switching, load driver & amplification circuits
  • Used in audio & RF amplifiers.

Thus, this is all about an overview of the BD139 NPN Transistor datasheet which includes its pin configuration, specifications, circuit working, and its applications. Here is a question for you, what are the different types of NPN transistors available in the market?