The working principle of basic common emitter amplifier circuit
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The working principle of basic common emitter amplifier circuit

Posted Date: 2024-01-25

The composition of the basic common-emitter amplifier circuit and the functions of each component

Transistors are components that play a role in amplification. The input signal u is a sine wave voltage.

Since this circuit is composed based on the voltage required when the transistor works in the amplified state bc, c=c, it is also called a principle circuit to distinguish it from a practical circuit.

R,VcT+4uWhen u=0, the amplifier circuit is said to be in static state.

In the input circuit, the base power supply VBB makes the voltage U between the transistors bc greater than the turn-on voltage U, and together with the base resistance R determines the base current l; in the output circuit, the collector power supply Vcc should be high enough to make the transistor's collector The junction is reverse biased to ensure that the transistor works in an amplified state, so the collector current lc=βIn; the current on the collector resistor Rn is equal to lc, so its voltage is, IcR1, thus determining the voltage between ce Ucr=VcclcRnV

Figure 2.2.1 Basic common-emitter amplifier circuit u When u is not 0, in the input circuit, a dynamic base current l will be generated based on the static value; of course, a dynamic current l will be obtained in the output circuit; The collector resistor R converts changes in the collector junction current into voltage changes, causing the tube voltage drop ucF to change. The change in the tube voltage drop is the output dynamic voltage u, thus achieving voltage amplification. DC power supply u, Vcc provides the required energy for the output.

The necessity of setting a static working point 1. Static working point From the above analysis, it can be seen that in the amplifier circuit, when there is a signal input, the AC quantity and the DC quantity coexist.

When the input signal is zero, that is, when the DC power supply acts alone, the transistor's base current, I, collector current lc, b = c voltage U, and tube voltage drop Uc are called the static operating point Q of the amplifier circuit. The four The physical quantity is recorded as ln0Ic0, UsEQ, and UcEQ. In approximate estimation, UnE0 is often considered to be a known quantity. For silicon tubes, U is taken to be a value from 0.6 to 0.8 V, such as 0.7 V; for germanium tubes, U is taken to be 0.1 to 0.3. A certain value in V, such as 0.2 V; and the penetration current is considered.

Ick0=0,β=β. In the circuit shown in Figure 2.2.1, let U=0, according to the loop equation, the expression of the static operating point can be obtained (2.2.1a) side A {Im side = Vm, 3Ux


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