What is a double base diode? The structure, working principle, working mode, characteristics, and application fields of double base diodes

Bipolar Junction Transistor (BJT) is a common electronic device widely used in circuits such as amplifiers, switches, and voltage regulators. It is composed of three doped semiconductor materials of different types, namely P-type semiconductor, N-type semiconductor, and P-type semiconductor, forming two PN junctions. According to different doping types, BJTs can be divided into NPN and PNP types.

1、 Structure

The structure of a dual base diode includes three regions, namely the emitter region, the base region, and the collector region. In NPN BJTs, the emitter and base regions are N-type semiconductors, and the collector region is P-type semiconductor; In PNP BJTs, the emitter and base regions are P-type semiconductors, and the collector region is N-type semiconductor. The junction between the emitter region and the collector region is called the emitter junction, and the junction between the base region and the collector region is called the collector junction.

2、 Working principle

The working principle of BJT is based on two basic physical effects: the drift and diffusion of holes in P-type materials and electrons in N-type materials under the action of an electric field. Under forward bias, the emitter junction is in a forward biased state, forming a state where electrons are injected into the emitter region; The base junction is in a reverse biased state, limiting the injection of electrons into the base region. When the electrons injected into the emission region recombine with the holes injected into the base region, a current amplification effect is generated.

3、 Working mode of BJT

BJTs have three working modes: amplification mode, cutoff mode, and saturation mode.

In amplification mode, the emitter junction of BJT is forward biased and the base junction is reverse biased. When an input signal is applied to the base, the current in the base region also changes due to the variation of the input signal. This change will cause a change in the current in the emission area, which in turn will affect the current in the collector area. By amplifying the input signal, the amplification of the output signal is achieved.

In cutoff mode, the emitter junction of BJT is reverse biased and the base junction is reverse biased. At this point, regardless of the magnitude of the input signal, the current at the base is very small, which affects the current in the emitter and collector regions, causing the BJT to be in a cutoff state.

In saturation mode, the emitter junction of BJT is forward biased and the base junction is forward biased. When an input signal is applied to the base, the current in the base region changes accordingly, resulting in changes in the current in the emitter and collector regions. At this point, the BJT is in a saturated state.

4、 Characteristics of BJT

BJTs have many important characteristics, such as amplification factor, input resistance, output resistance, switching speed, etc.

Amplification factor refers to the ratio of input signal to output signal, used to measure the amplification capability of BJT. It can be calculated by measuring the current or voltage of the input and output signals.

The input resistance refers to the resistance property that the input signal needs to overcome, which depends on the structure and doping concentration of the BJT. The larger the input resistance, the greater the resistance that the input signal needs to overcome, making it easier for the input signal to pass through the BJT.

The output resistance refers to the resistance property that the output signal needs to overcome, which also depends on the structure and doping concentration of the BJT. The smaller the output resistance, the smaller the resistance that the output signal needs to overcome, making it easier for the output signal to pass through the BJT.

Switching speed refers to the switching speed of BJT from off mode to saturation mode or from saturation mode to off mode. It is usually determined by the structural characteristics and doping concentration of BJTs.

5、 Application Fields

Due to its functions of amplification, switching, and voltage stabilization, dual base diodes are widely used in electronic circuits. In amplification circuits, BJTs can amplify weak signals to larger amplitudes, which are used for audio amplification, RF amplification, etc; In switch circuits, BJTs can achieve switching functions and are used for electronic switches, computer logic gates, etc; In voltage regulator circuits, BJTs can provide stable voltage outputs for power regulators, voltage regulator diodes, and other applications.

In summary, dual base diodes, as an important electronic device, have multiple functions and applications, making significant contributions to the development of electronic technology