The working principle and state of transistors

Transistor is a semiconductor device that is one of the prerequisites for modern electronic technology. It can be used to amplify electrical signals, switching circuits, and oscillators. Transistors are made of semiconductor materials, usually silicon (Si) or germanium (Ge). The appearance of a transistor is usually a small chip that can be installed on a circuit board. Next, this article will briefly introduce the operating principles and three operating states of transistors. Let's take a look!

A transistor has three regions: a P-type semiconductor region, an N-type semiconductor region, and a P-N junction region. The number of electrons in the P-type semiconductor region decreases, while the number of electrons in the N-type semiconductor region increases. When the P-type contacts the N-type region, a P-N junction is formed. In the P-N junction region, electrons flow from the N-type region to the P-type region, and holes flow from the P-type region to the N-type region. This flow is called drift flow.

The operating principle of transistors is based on the electrical characteristics of P-N junctions. For example, if a positive voltage is added in the P-type region, but a negative voltage is added in the N-type region, P-when the transistor is turned off, the N-junction will generate a reverse bias. If a negative voltage is added in the P-type region, but a positive voltage is added in the N-type region, P-when the transistor is in the ON state, a positive bias occurs at the N-junction.

The three operating modes of transistors are common base, common emitter, and common collector. These operating modes are named according to the circuit connection method of the three regions in the transistor, and the current and voltage of the transistor are mastered to achieve different circuit effects.

Common base (CB) operating mode

In the common base operation mode, the base of the transistor is used as the input terminal, the emitter is used as the output terminal, and the collector is used as the common terminal. The input signal is applied to the base electrode and the output signal is obtained from the emitter electrode. In this mode of operation, the voltage growth of the power supply is small, but the current growth is large. Therefore, it is commonly used in high-frequency amplification circuits and circuit thrusters.

Common emitter (CE) operating mode

In the common emitter mode of operation, the emitter of the transistor is used as the input terminal, the collector is used as the output terminal, and the base is used as the common terminal. The input signal is applied to the emitter and the output signal is obtained from the collector. In this mode of operation, the voltage and current increase of the power supply is very large, so it is commonly used in amplifier and switching circuits.

Common collector (CC) operating mode

In the common collector mode of operation, the collector of the transistor is used as the input terminal, the emitter is used as the output terminal, and the base is used as the common terminal. The input signal is applied to the collector and the output signal is obtained from the emitter. In this mode of operation, the voltage of the power supply increases greatly, but the current increase is small. Therefore, it is commonly used for circuit buffers and circuit thrusters.

These three operating modes have their own characteristics and application areas, so it is necessary to select appropriate operating modes in actual circuits to achieve the required circuit functions.