We also show you more details about a NPN bipolar transistor as is the case of the BD139. One of the most used transistors, along with the BD140, and which can be quite practical for a multitude of DIY electronics projects, since it has an infinite number of possible applications.
In this article you will learn more about this electronic component and we will show an example of a circuit Where could this transistor be used? So, let's look at the basics so you can get started with your own projects based on the BD139.
What is an NPN bipolar transistor? and how it works
Un NPN bipolar transistor It is a three-terminal semiconductor device commonly used in electronics. The letters N and P refer to the types of semiconductor, and the NPN configuration indicates the sequence of layers of semiconductor material within the device.
The operation of the NPN transistor is based on the control of a relatively small current in one terminal (the base) to control a much larger current in two other terminals (the collector and the emitter). To do this, these transistors will have different junctions and structure than MOSFETs, in this case we have three regions and two junctions. An N region acting as an emitter cone, a P region acting as a base, and an N region acting as a collector. That is, a kind of semiconductor sandwich that can function thanks to the majority charge carriers in the N regions, which are the electrons, and the majority carriers of the base, which are the holes that act as a positive charge.
When the NPN transistor is acting in forward bias, with a positive voltage at the emitter with respect to the base, the electrons from the emitter are injected towards the base region. On the other hand, when it acts as an amplifier, the base region narrows and this allows most of the electrons injected from the emitter to be attracted by the electric field of the collector, which is connected to a more positive potential. If it acts in saturation mode, the transistor will function as a closed switch, without allowing current to pass. On the other hand, in cut-off mode the transistor acts as an open switch, allowing current to flow.
These characteristics of NPN mean that these transistors can have a multitude of applications such as amplifiers, switches, oscillators, logic inverters, and more.
What is BD139?
El BD139 is a low power NPN bipolar transistor, designed for general applications such as low-power audio amplifiers, drivers and complementary circuits. The truth is that it can be present in very diverse projects.
Technical characteristics and pinout of the BD139
The technical characteristics Typical (they may vary slightly depending on the manufacturer), but they can basically be the following:
- Maximum collector-emitter voltage (VCEO): around 45V (allows a potential difference of up to 45V between collector and emitter)
- Maximum continuous collector current (Ic): typically 100mA (the maximum current you can drive continuously between collector and emitter)
- Current gain (hFE)- Varies between different units, but is usually in the range of 100-300 (indicates the ratio between collector current and base current)
- Dissipation power- Depends on packaging, but is usually around 0.6W (the amount of power it can dissipate without overheating)
- Packaging: usually in SOT-32 format, a small plastic package, although it can also come in other forms.
In the case of pinout, it is very simple, as happens in transistors, since we will always have three pins or terminals for connection. In this case, if we look at the BD139 transistor from the front, that is, from the part where the inscriptions appear as in the previous image, then we have pin 1 on the left, 2 in the center and 3 on the right, being 1 the emitter, 2 the collector and 3 the base. It is important to keep this in mind to know how it is connected properly and for its correct polarization, depending on what we want to use it for...
Where to buy
If you would like to acquire a BD139 (NPN) or BD140 (PNP) transistor, can be found in many specialized electronics stores, both physical and online. However, you can also find them on platforms such as ALiexpress, Amazon, etc., here we make it easy for you and show you the transistors at the best price:
An example of a sound amplifier circuit with the BD139 and BD140
El pair of transistors BD139 (NPN) and BD140 (PNP) It is a classic combination for building low power audio amplifiers very easily. They work in a complementary way, expanding the input signal and delivering a higher power output.
A basic audio amplifier with BD139 and BD140 usually has an input for lto audio signal that you want to amplify, such as a 3.5mm jack that comes from an MP3 player, from a PC, etc. This signal will be applied to the emitter and collector of the BD139 as shown in the image. In this way, by controlling the base of this transistor, it can be used in amplifier mode to amplify the signal. The BD140 transistor will act as a mirror of the BD139, complementary, this allows both the positive and negative part of the audio signal that you want to amplify to be amplified correctly, and thus obtain the amplified output that can be connected to a speaker to check the result.
That is, both the NPN and PNP transistors aim to amplify the negative and positive part of the audio input signal, thus achieving the desired effect in this application, although many more projects could be built with the BD139, but the rest of creativity and practices now I leave them in your hands...
Interesting article, as always, but a traditional electrical diagram is missing to understand the connection well. And what value is the resistance? It seems like an unripe article.