Principles of operation of the transistor

A transistor is a device that operates on semiconductors with electronic stuffing. It is designed to convert and amplify electrical signals. There are two types of devices: a bipolar transistor and a unipolar transistor, or a field transistor.

If two types of charge carriers - holes and electrons - operate simultaneously in a transistor, then it is called bipolar. If only one type of charge operates in the transistor, then it is unipolar.

Imagine the work of an ordinary water crane. Turned the latch - the flow of water increased, turned to the other side - the flow decreased or stopped. In practice, this is how the transistor works. Only instead of water, a stream of electrons flows through it. The principle of operation of a bipolar type transistor is characterized by the fact that two types of current flow through this electronic device. They are divided into large, or basic and small, or manager. Moreover, the power of the control current affects the power of the main current. Consider a field effect transistor. The principle of its operation differs from others. Only one current passes through it , the power of which depends on the surrounding electromagnetic field.

Bipolar transistor is made of 3 layers of semiconductor, and, most importantly, of two PN transitions. It is necessary to distinguish between PNP and NPN transitions, and, hence, transistors. In these semiconductors there is an alternation of electron and hole conductivity.

The bipolar transistor has three contacts. This is the base, the contact emerging from the central layer, and the two electrodes along the edges - the emitter and collector. In comparison with these extreme electrodes, the interlayer of the base is very thin. At the edges of the transistor, the semiconductor region is not symmetrical. For proper operation of this device, the semiconductor layer located on the collector side should be a little thicker than the emitter side.

The principles of the transistor are based on physical processes. We will work with the PNP model. The operation of the NPN model will be similar, except for the polarity of the voltage between such basic elements as the collector and emitter. It will be directed in the opposite direction.

The P-type substance contains holes or positively charged ions. The N-type substance consists of negatively charged electrons. In the transistor considered by us, the number of holes in the region P is much larger than the number of electrons in the region N.

When connecting a voltage source between parts like the emitter and the collector, the transistor's operating principles are based on the fact that the holes begin to attract to the pole and collect near the emitter. But the current does not go. The electric field from the voltage source does not reach the collector because of the thick interlayer of the emitter semiconductor and the interlayer of the base semiconductor.
Then we connect the voltage source with another combination of elements, namely between the base and the emitter. Now the holes are directed to the base and begin to interact with electrons. The central part of the base is filled with holes. As a result, two currents are formed. Large - from the emitter to the collector, small - from the base to the emitter.

With an increase in the voltage in the base in the interlayer N there will be even more holes, the base current will increase, the emitter current will increase slightly. Hence, with a small change in the base current, the emitter current is seriously increased. As a result, we get a signal growth in a bipolar transistor.

Let's consider the principles of the transistor operation depending on the modes of its operation. There are normal active mode, inverse active mode, saturation mode, cut-off mode.
With the active mode of operation, the emitter junction is open, and the collector junction is closed. In inversion mode, everything happens the other way around.