Transistor symbol and amplification
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Transistor symbol and amplification

Posted Date: 2024-02-06

The transistor has electrodes called collector, base and emitter, which are represented by the first letters of the English letters: collector-C (collector), base-B (base), and emitter-E (emitter). The symbols for transistors are shown in the figure.

Transistors are divided into PNP type and NPN type, and the symbols in the diagram are distinguished by the direction of the emitter arrow. Remembering that there is an N in front of the arrow can help with memory. Arrows also indicate the direction of current flow.

The main purpose of using a transistor is to amplify it and transform small signals (such as weak current changes that can only be heard with headphones) into powerful signals (large current changes that can make the speaker sound).

For this reason, there will be problems if the state of a small signal change cannot be converted into a strong signal change unchanged. When considering this issue, careful readers will find that the aforementioned changes in IE and IC have the same nature. Specifically, in the circuit, if a small signal source (AC) is sandwiched between the emitter and the field of the battery, the change of the current IE will be caused by the superposition of DC and AC. Compared with the small signal source, this change does not change the waveform at all except for the difference in potential size.

Because changes in IE are "faithfully" converted into changes in IC, as long as the resistor RL is connected to the collector terminal, the IC will flow through RL. At this time, as long as the resistance value is large, it can be treated as a strong voltage change (output) take out.

The transistor has 3 terminals, and to amplify the signal, it must have 2 input terminals and 2 output terminals, a total of 4 terminals, so one terminal must be shared.

Review Editor: Huang Fei


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