Non-exam preparation materials
1.18 (1.17 type code to go)
Chapter 14 Semiconductor Devices
Use the following photoelectric devices for display, alarm, coupling and control.
Light-emitting diode (LED): forward voltage + sufficiently large forward current => luminescence (the result of the recombination of electrons and holes to release energy) working voltage: 1.5-2.5V, generally used for display.
Photodiode: Use the photosensitivity of the PN junction to convert the changes in received light into changes in current. Work under reverse voltage. When there is no light, it is equal to an ordinary diode (dark current). When there is light, the stronger the light, the greater the photocurrent, but it must be amplified during application.
Phototransistor: Unlike ordinary transistors that use base current to control the collector current, the phototransistor uses the intensity of incident light to control the collector current.
Coupling and control: photoelectric coupling amplifier circuit, light-emitting diode and phototransistor (photodiode) coupling
When the light path between the light-emitting diode and the phototransistor is blocked (no light), the output transistor is cut off, uo=VCC, when there is light, the output transistor is saturated and turned on, and uo is approximately equal to 0V to achieve the control (switch) effect.
Chapter 15 Basic Amplification Circuit
One of the uses of the transistor is to use its amplifying effect to form an amplifying circuit, and use a weak signal to control a higher power load. The fifteenth chapter is about various common basic amplifying circuits composed of discrete components.
Expand knowledge:
1. Discrete component circuit: a circuit formed by connecting individual electronic components. If discrete components are used to implement circuits or systems with complex functions, it will inevitably result in a large number of components, increase in volume, weight and power consumption, and poor reliability.
2. Integrated circuit: It is a circuit formed by using a certain manufacturing process to make all components on a small piece of silicon. Its advantages are low cost, small size, light weight, low power consumption, high reliability, and easy maintenance. The application of integrated circuits is very wide and the development is very rapid.
3. The difference between discrete component circuits and integrated circuits: in digital circuits, discrete component circuits are almost eliminated; in analog circuits, due to the diversity of signal shapes, the diversity of power requirements, and integrated circuit manufacturing technology, etc. It is impossible to realize components such as large-resistance resistors, large-capacity capacitors, inductors, and transformers inside integrated circuits. Therefore, discrete component circuits still have a place in the fields of high-power and ultra-high frequency analog circuits.