In the development of both domestic and global electrical engineering and electronics, a semiconductor device such as a bipolar transistor played a key role.
A bipolar transistor is a device that incorporates two interconnected pn junctions and is based on semiconductor materials. This type of transistor has from three terminals. The amplification characteristics possessed by a bipolar transistor are explained on the basis of knowledge about the enrichment and depletion of semiconductor wafers by charges (injection and extraction procedures are carried out, respectively), as well as the laws of electromagnetism.
Today, there are two main types of bipolar transistors, which are distinguished depending on how the alternation of regions of different types of conductivity occurs in the used semiconductor sample: types npn and pnp. The advantages of one type over another cannot be distinguished, because the difference between these types of transistors is only in what polarity of the external power source is connected to one or another terminal of the device.
A transistor is a bipolar device consisting of three main elements: a collector, an emitter, and a base. As a rule, one terminal is connected to each element.
Bipolar transistors are often classified by the power dissipated from the collector. According to this parameter, the devices are divided into transistors of low power (about 0.3 W), medium (from 0.3 to one and a half watts) and large (more than 1.5 W). Another principle for the classification of transistors is in the working frequency range. With this principle of separation of devices, devices of low frequencies (up to five MHz), medium frequencies (from 5 MHz to 35 MHz), high-frequency (from 35 MHz to 350 MHz) and ultra-high-frequency (above 350 MHz) transistors are distinguished.
Each bipolar transistor is labeled in accordance with accepted government standards. Typically, a designation consists of six or seven characters (numbers or letters). The marking must indicate the type of material, the type of device itself, frequency characteristics and power of the device. Also, by marking, you can determine the type and serial number of the development of the device. Thus, the designation of the transistor is a passport of the device, which reveals all the key characteristics of the device.
There are four main modes of operation of a bipolar transistor:
- active mode, in which the transition at the emitter opens and the transition at the collector closes;
- a cutoff in which both junctions (both the emitter and the collector) are closed and do not pass current in the forward direction;
- saturation - a mode opposite to the cutoff, in which transitions on the collector and emitter are opened;
- inversion (inverse mode) is the phase when the collector junction opens and the emitter shifts in the opposite direction (does not pass “direct” current).
Depending on which of the electrodes (terminals) of the transistor becomes common in the amplification stages for both the input and output current, there are three main types of switching the device into a circuit: a bipolar transistor with a common emitter, collector or base. Depending on what type of device switching is used in one or another stage, various 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 us 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.