Answer to Question #143057 in Electrical Engineering for Unknown

Question

6. Explain the VI characteristics of Common Emitter NPN Transistor with all necessary diagrams?

Answer 1

Circuit of the transistor

The amplifier is a four-pole device with two outputs for connecting the input signal and the remaining two outputs for removing the amplified signal (voltage or current) from them. The transistor has only three outputs, so to implement a four-pole device, you have to connect one of the pins to both the input and output of the amplifier. Depending on which output of the transistor is shared, both for the input and output of the amplifier, the switching circuits of the transistor are called:

 

The circuit with common emitter

The scheme with a common base

It should be noted that these switching circuits are used not only for bipolar transistors, but also for all types of field-effect transistors. In them, these schemes will be called schemes with a common source, a common gate, and a common drain, respectively. In all subsequent diagrams, the boundaries of the four-pole amplifier will be shown as a dotted line. To connect the signal source and load, they have two outputs each.

 

The circuit with common emitter

The most common circuit for switching on a transistor is a common emitter (OE) circuit. This is due to the highest power gain of this circuit. A common emitter circuit has both voltage and current amplification. The functional diagram of switching on a transistor with a common emitter is shown in figure 1.

 

Figure 1. Functional diagram of switching on a transistor with a common emitter

The scheme with a common base a common-base circuit is usually used at high frequencies. The power gain of this transistor switching circuit is less than that of a common emitter circuit. This is due to the fact that the switching circuit of a transistor with a common base does not amplify the current. In this scheme, only voltage amplification is performed. The functional diagram of switching on a transistor with a common base is shown in figure 2.

 

Figure 2. Functional diagram of switching on a transistor with a common base

Scheme with a common collector a common collector circuit is usually used to obtain a high input resistance. The power gain of this transistor switching circuit is less than that of a common emitter circuit and is comparable to the gain of a common base circuit. This is due to the fact that the switching circuit of a transistor with a common collector does not amplify the voltage. In this scheme, only current amplification is performed. The functional diagram of switching on a transistor with a common collector is shown in figure 3.

 

Figure 3. Functional diagram of switching on a transistor with a common collector