LOTO Lesson 4: Practice of the common emitter amplifier circuit of transistor 2N3904

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LOTO Lesson 4: Practice of the common emitter amplifier circuit of transistor 2N3904 [Copy link]

The basic amplifier circuits of triodes include common emitter amplifier circuit, common base amplifier circuit and common collector amplifier circuit, among which the common emitter amplifier circuit is the most widely used connection method. The figure below shows the principle of the triode common emitter amplifier circuit, with input on the left and output on the right. The emitter (e) is the common terminal of the input and output, so it is called a common emitter amplifier circuit.

Today's video is to build a transistor amplifier circuit like the one shown above, and observe the waveform of the input and output signals of the entire circuit with the help of the LOTO oscilloscope and signal generator module. Our physical circuit diagram is based on the 2N3904 transistor, Rb=300K, Rc=1K; after many experiments, we have adopted this pair of resistance values to keep the transistor in the amplification area as much as possible and away from the cutoff area and saturation area. The physical diagram of the circuit is shown in the figure below.

The specific process of the video is as follows:

https://www.bilibili.com/video/BV1fi4y1t79b/

After connecting our circuit, opening the oscilloscope's host computer software, we can clearly see that the output signal is amplified many times compared to the input signal. At the same time, due to the circuit characteristics of the common-emitter amplifier circuit, the amplified output signal is the reverse amplification of the input signal. By comparing the waveform phases in the figure, we can intuitively see that the output signal and the input signal are amplified in reverse.

Think about it: Why is the output of the triode common-emitter amplifier circuit reversely amplified?

As the base input voltage increases, the base current increases, and the collector current also increases. As the collector current increases, the voltage on the collector resistor increases. The collector output voltage = power supply voltage minus collector resistor voltage, so the collector output voltage decreases. In other words, as the base input voltage increases, the collector output voltage decreases. That is: reverse

MartinFowler

Thanks to the host

okhxyyo

Thank you for sharing~~

luwei100

The following uses the NPN transistor as an example to illustrate its internal carrier movement law and current amplification principle. 1. Electrons diffuse from the emitter region to the base region: Since the emitter junction is in forward bias, the majority carriers (free electrons) in the emitter region continuously diffuse to the base region, and are continuously replenished with electrons from the power supply to form the emitter current IE. 2. Electrons diffuse and recombine in the base region: Since the base region is very thin, its majority carrier (hole) concentration is very low, so only a small part of the electrons diffused from the emitter can recombine with the base holes to form a relatively small base current IB, and most of the remaining electrons can diffuse to the edge of the collector junction. 3. The collector region collects electrons diffused from the emitter region: Since the collector junction is reverse biased, the electrons diffused from the emitter region to the base region and reach the edge of the collector region can be pulled into the collector region, thereby forming a larger collector current IC

nian1206

Mark it and I will use it later. Thank you very much for sharing. May good people have a peaceful life!