Bipolar transistor is the main device for amplifying electrical signals

In the development of both domestic and global electrical engineering and electronics, a semiconductor device, such as a bipolar transistor, played a key role.

Bipolar transistor is a device that has two interconnected pn junctions and is based on semiconductor materials. This type of transistor has three terminals. The amplifying characteristics that a bipolar transistor possesses are explained on the basis of knowledge about enrichment and depletion of semiconductor plates by charges (injection and extraction procedures are conducted, respectively), as well as electromagnetism laws.

Today, there are two main types of bipolar transistors that are distinguished depending on how the regions of different conductivity alternate in the sample of the semiconductor used: npn and pnp. Advantages of one type over another can not be distinguished; The difference between these types of transistors is only in what kind of polarity of the external power source is connected to this or that terminal of the device.

Transistor is a bipolar device consisting of three main elements: a collector, an emitter and a base. To each of the elements, as a rule, one terminal is connected.

Bipolar transistors are often classified according to the power dissipated from the collector. In this parameter, the devices are divided into low power transistors (about 0.3 W), medium (0.3 to 1.5 W) and large (more than 1.5 W). Another principle of the classification of transistors is the operating frequency range. With this principle of separation, low-frequency devices (up to five MHz), medium frequencies (from 5 MHz to 35 MHz), high-frequency (from 35 MHz to 350 MHz) and ultrahigh-frequency (over 350 MHz) transistors are singled out.

Each bipolar transistor is labeled in accordance with accepted state standards. As a rule, the designation consists of six or seven symbols (numbers or letters). The marking must indicate the type of material, the type of the device, the frequency characteristics and the power of the device. Also, by marking, you can determine the type and serial number of the device development. Thus, the designation of a transistor is the instrument's passport, which reveals all the key characteristics of the device.

There are four main operating modes of the bipolar transistor:

• Active mode, which opens the transition to the emitter and closes the transition to the collector;
• Cutoff, in which both the junction (both the emitter and the collector) are closed and do not pass current in the forward direction;
• Saturation - a mode opposite to the cut-off, at which transitions are opened on the collector and emitter;
• Inversion (inverse mode) - phase, when the collector junction is opened, and the emitter is displaced in the opposite direction (does not pass the "direct" current).

Depending on which of the electrodes (terminals) of the transistor becomes common in the amplification stages for both the input and the output current, three main types of switching the device into a circuit are identified: a bipolar transistor with a common emitter, collector or base. Depending on what type of device switching is used in this or that cascade, different advantages of the transistor can be used.

In conclusion, we note that today bipolar transistors are widely used in electrical engineering and analog electronics. These devices are used in various amplification stages, without them it would not be possible to create an operational amplifier - a device that allowed to create a transition from analog to digital circuitry. Therefore, a bipolar transistor can be considered one of the fundamental semiconductor devices that laid the foundation for the development of modern electrical engineering.