2. Semiconductor components

Semiconductors such as diodes or transistors are the silicon-based components that have developed modern electronics to the point of transforming our entire society.

In this unit we will study the fundamentals of electronic components, their operation and typical electrical diagrams.

The semiconductor components. PDF format.

The semiconductor components. Editable DOC format.

The semiconductors

Insulating materials such as plastic or wood do not allow the passage of electric current. Conductive materials such as copper or aluminum allow the passage of electric current very easily. On the other hand, semiconductor materials such as silicon or germanium can behave as insulators or conductors depending on the voltage they receive. This behavior can be exploited to make circuits that have very fast, electronically controlled semiconductor switches.

For semiconductors to be able to conduct current, it is necessary to alloy them with traces of elements that provide positive charges (Boron, Indium, etc.). or negative charges (Phosphorus, Arsenic, etc.) So that an already alloyed semiconductor can be called type P (positive) or type N (negative).

The diode

It is the simplest electronic component that can be made with semiconductor materials and has two terminals. Internally it is formed by the union of a P-type silicon block with a N-type silicon block. This junction allows current to flow in one direction, but does not allow it to flow in the opposite direction.

In the previous image you can see the symbol of the diode, an arrow in the direction in which it allows the flow of current and the name of its two terminals. The diode only conducts when the anode has positive voltage and the cathode has negative voltage.

The following image is a photograph with various types of diodes.

Diodes have multiple applications. For example, rectifying alternating current, regulating voltages or emitting light (LED diodes).

Schematic of a polarized LED diode with a resistor that reduces the current so that it does not burn out.

Schematic of a rectifier diode that converts the alternating voltage of the electrical network into direct voltage.

The transistor

The transistor is a three-terminal electronic component that allows the passage of electric current between two terminals depending on the voltage received by the third terminal. It's like a voltage controlled switch. The first silicon transistor was marketed in 1954.

Power transistor

Signal transistor.

Transistor states

Depending on the control voltage that the transistor receives through the base or through the gate, it can be in three different states.

Cut: the transistor does not conduct current, it behaves like an open switch.

Saturation: the transistor conducts all possible current and behaves like a closed switch.

The above two states are used in digital circuits such as a computer, TV, smartphone, etc.

Linear zone: the transistor only conducts part of the current and behaves like a resistor.

This behavior is used in analog circuits such as sound amplifiers.

Typical circuits

Amplifying transistor. This circuit works like a light amplifier. When the LDR resistor is illuminated, the current through it increases. That current reaches the base of the transistor and the transistor amplifies it through the collector, turning on the connected lamp. This is an analog circuit because the transistor works in a linear zone, behaving as a resistor controlled by the base current.

Amplifying transistor.

Digital transistor. This circuit is a NOR logic gate formed from transistors. Thanks to the parallelization of the two collectors, the output only has high voltage when the two inputs are at low voltage. These logic gates are the basis of digital circuits and computers.

Digital transistor.

LDR resistors

LDRs (Light Dependent Resistors) are, as their name suggests, sensors that detect light. Their resistance is reduced when the illumination is greater, increasing the current they conduct the more light they receive.

Symbol and photograph of an LDR resistor.

Integrated circuits

An integrated circuit is a small silicon chip, also called a chip, that contains a multitude of electronic components inside.

LM555 integrated circuit.

DAC08 integrated circuit.

With the development of technology, the size of the components is reduced more and more each year, making it possible to group more and more transistors into a single integrated circuit. In the early 1960s the aerospace industry began purchasing circuits that integrated up to 100 transistors on a single chip. This lowered production prices and encouraged the development of technology. At the beginning of 1980 you could already buy chips with 100 thousand transistors, in 2000 100 million transistors and in 2020 100 billion transistors on a single chip. This exponential growth in the number of transistors integrated into a chip, which doubles every year and a half, is known as Moore's law and has allowed the development of the digital society that we all know, with a multitude of smart devices, memories, cameras, drones, etc. . based on these powerful integrated circuits.

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Exercises

1. What types of materials are there depending on how they conduct electricity? Write two examples of each.
2. Why are semiconductors so useful?
3. What needs to be done for a semiconductor to conduct electric current?
4. How is a semiconductor diode constructed?
5. Draw the symbol of a semiconductor diode and name its terminals.
6. When does a diode conduct current?
7. Draw two electrical diagrams with diodes.
8. What applications do diodes have?
9. What is a transistor? How many terminals does it have?
10. What states can a transistor have?
11. What transistor states are used in analog circuits? And in digital ones?
12. Draw the symbol of a bipolar transistor and a MOSFET with the name of their pins.
13. Draw a circuit with a transistor functioning as a light amplifier.
14. Draw a NOR logic gate with transistors.
15. What is an LDR and what do those acronyms mean?
16. What is an integrated circuit or chip?
17. When did integrated circuits begin to be manufactured and how many transistors did they have?
18. Draw a graph with the number of transistors a chip contains. Place the years on the
19. What is Moore's law?