Semiconductor Components: Diodes, Transistors, and Capacitors
Semiconductor Materials and Their Applications
The primary semiconductor material is silicon, as it is an inexpensive and abundant material on Earth’s crust. Other notable semiconductor materials include germanium and gallium arsenide. These materials are used to construct active electronic components, which perform the core functions of electronic circuits.
Diodes: Unidirectional Current Flow
Rectifying Diodes
Diodes are electronic components that allow electric current to pass in only one direction. They consist of two semiconductor crystals, typically silicon or germanium, joined together. When the positive terminal of the diode is connected to the positive terminal of a battery, the diode conducts like a closed switch, allowing current to flow. In this case, the diode is said to be forward-biased. Conversely, when the positive terminal of the diode is connected to the negative terminal of the battery, it behaves like an open switch, preventing the flow of electricity. In this scenario, the diode is reverse-biased.
Rectifying diodes are used to convert alternating current (AC) into direct current (DC).
Light-Emitting Diodes (LEDs)
LEDs are available in various colors (red, green, yellow, white) and emit light when forward-biased. They are commonly used as indicators in many signaling devices. Another application is in remote controls.
Rectifier Diode (cathode side identifies +) symbol
LED
Capacitors: Storing Electrical Charges
A capacitor is a component used to store electrical charges and release them when needed. However, its capacity to store charges (electrons) is relatively small, which is why it is not used as a battery. It consists of metal plates (typically aluminum) separated by a dielectric material, such as an upper interface, paper, or ceramics.
The symbol of a capacitor is:
Function: When the switch is open, the capacitor is disconnected. Upon closing the switch, the capacitor is connected to the power source, leading to an accumulation of electric charges (electrons) on the two plates of the capacitor. If the switch is opened, the capacitor is disconnected, but the accumulated charge is retained. The capacity of a capacitor to store charge is measured in Farads (F).
Transistors: Controlling and Amplifying Current
Understanding Transistor Operation
The characteristics of diodes are voltage (typically 3V or 2V) and operating current (approximately 20mA). Therefore, to connect an LED to voltages higher than 2V or 3V, a resistor, known as a limiting resistor, is connected in series.
The transistor is a three-terminal electronic component that can control the flow of current between two terminals by varying the current through the third terminal. In other words, it can act as a switch that opens or closes depending on the current applied to the third terminal, allowing or preventing the flow of electrical current. It also has an amplifying effect, similar to the amplifier in a stereo system, which uses transistor circuits to amplify (increase) the electrical signal that carries sound to the loudspeakers.
- Switch-controlled electrical current: Transistors can act as switches to control the flow of current.
- Signal amplification: Transistors can amplify signals, as seen in stereo amplifiers.
Transistor Operating Modes
- Cut-off: When no electrons flow into the base (B), there is no movement of electrons between the collector and emitter. The transistor is said to be in cut-off mode, and the collector and emitter are isolated. In this state, the transistor does not conduct at all and is effectively inactive. It behaves like an open switch.
- Active: When a small number of electrons are introduced into the base, it provides enough energy to partially open a metaphorical”gat” in a dam. As more electrons enter the base, the gate opens further, allowing more current to flow between the collector and emitter. In this mode, the transistor operates as an amplifier. The collector current is directly proportional to the base current. For example, if the gain (A) is 100, the collector current is 100 times the base current.
- Saturation: If a large number of electrons flow through the base, the metaphorical”dam gat” can be fully opened. The collector and emitter are effectively connected, and electrons flow freely between them. In this mode, the transistor acts as a closed switch.