Non-exam preparation materials
1.19
Chapter 15 Basic Amplification Circuit
The essence of amplification: the input signal with lower energy is controlled by the transistor to control the energy supplied by the power supply UCC to obtain a signal with higher energy at the output.
Circuit 1: Common emitter amplifier circuit
Part of the role of components:
resistance: bias, current to voltage;
capacitance: DC blocking, AC coupling (capacitance value should be large enough to make its capacitive reactance to AC frequency approximately zero)
Application: Microphones and speakers (restore and amplify sound signals); automatically control machine tools (obtain a certain output power to drive actuators, electromagnets, motors, etc.); radios and televisions (antennas).
Transistor is a non-linear element, but you can use the micro-variable equivalent circuit method to linearize the transistor, which is equivalent to a linear element.
It is usually desirable that the input resistance of the amplifier circuit be higher and the resistance of the output stage lower.
Circuit 2: Voltage divider bias amplifier circuit (AC bypass capacitor, emitter resistance)
Expand knowledge:
1. A non-polar capacitor is a capacitor without the positive and negative poles of the polar power supply. The two electrodes of the non-polar capacitor can be freely connected in the circuit. Because this capacitor has no leakage phenomenon, it is mainly used in coupling, decoupling, feedback, compensation, and oscillation circuits.
2. Polar capacitors are capacitors such as electrolytic capacitors, in which two electrodes are formed by the aluminum foil of the anode and the electrolyte of the cathode, and the aluminum oxide film produced on the anode aluminum foil is used as the dielectric.
3. The so-called load capacity means that the output resistance of the circuit is the same as the internal resistance. For example, in an amplifying circuit, if you want to obtain a stable voltage at the load, that is, the output voltage changes little when the load changes, then the output resistance of the amplifying circuit is required to be as small as possible (basically not involved in voltage division).