Circuit composition and principles of transistor amplification circuit

Composition of transistor circuit

The basic amplification circuit of the common emitter configuration is that the input signal is applied between the base and emitter, and the coupling capacitors C1 and Ce are considered as short circuits to the AC signal. The output signal is taken out from the collector to ground and separated from the DC by coupling capacitor C2,

Only apply the AC signal to the load resistor RL. The common emitter configuration of an amplifier circuit actually refers to the common emitter configuration of the transistors in the amplifier circuit.

When the input signal is zero, the DC power supply provides DC base current and DC collector current to the transistor through various bias resistors, and forms a certain DC voltage between the three poles of the transistor. Due to the DC blocking effect of the coupling capacitor,

DC voltage cannot reach the input and output terminals of the amplification circuit.

When the input AC signal is applied to the emitter junction of the transistor through coupling capacitors C1 and Ce, the voltage on the emitter junction becomes a superposition of AC and DC. The situation of signals in amplification circuits is quite complex, and the symbols of each signal are defined as follows:

The current amplification effect of the cathode ray tube, IC, is several tens of times larger than IB. Generally speaking, as long as the circuit parameters are set appropriately, the output voltage can be many times higher than the input voltage. A portion of the AC in uCE passes through the coupling capacitor and reaches the load resistor,

Generate output voltage. Complete the amplification function of the circuit.

From this, it can be seen that the DC signal at the collector of the transistor in the amplification circuit does not change with the input signal, while the AC signal changes with the input signal. During the amplification process, the collector AC signal is superimposed on the DC signal and coupled

Capacitors only extract AC signals from the output terminal. Therefore, when analyzing amplification circuits, the method of separating AC and DC signals can be used, which can be divided into DC and AC paths for analysis.

Composition principle

1. Ensure that the core component of the amplification circuit, the transistor, operates in the amplification state with appropriate bias. That is to say, the emitter is positively biased and the collector is negatively biased.

2. The setting of the input circuit should couple the input signal to the input electrode of the transistor, forming a changing base current, thereby generating a current control relationship of the transistor, which becomes a change in collector current.

3. The setting of the output circuit should ensure that the current signal amplified by the transistor is converted into the form of the amount of electricity required by the load (output voltage or output current).