1. Electronic Conditioners
Unit 11

2. Objectives Describe basic semiconductor theory.
Describe basic transistor theory.
Describe an IC.
Describe how an op-amp works.
Describe how an audio-transformer works.

3. An electronic conditioner is any device that conditions or changes a voltage or wave form. Many electronic conditioners can be found in everyday life in radios, microwave ovens, automobiles and airplanes. Electronic conditioners include transistors, diodes, regulators, op-amps, audio-transformers, and integrated circuits (IC’s). In modern society we take these components for granted, yet we could not function without them. Basic semiconductor theory has existed since the 1930’s. But the transistor was not invented until the late 1940s because manufacturing technology had not sufficiently advanced until then. The first transistor was invented by John Bardeen, William Shockley, and Walter Brattain at Bell Labs in New Jersey. The invention won the trio a Nobel Prize in Physics.

4. To understand semiconductors, you must first recall what you already learned about atoms. An atom consists of a nucleus made of protons and neutrons, surrounded by electrons that orbit the nucleus. The number of protons and electrons in an atom are equal. The electrons have negative charges that are equal to the positive charges of the protons in the nucleus. This balance permits electroneutrality , which means the positive and negative charges are exactly balanced and the atom has no net charge or is neutral.

5. The electrons of an atom move around the nucleus in paths called energy levels. Not all electrons in an atom share the same energy level. For example, an oxygen atom has 8 protons in its nucleus and 8 electrons orbiting the nucleus with 2 of its electrons in the first energy level and 6 electrons in its second energy level.

6. You can compare the energy levels of an atom to steps on a staircase
You can compare the energy levels of an atom to steps on a staircase. An electron can be on one step or the next, but not in-between steps. When an electron absorbs energy, it moves to a higher energy level, or one farther from the nucleus. When an electron loses energy, it falls to a lower energy level. The flow of electricity through a material depends on the electrons in the outer energy level of the atoms. These electrons are called valence electrons. The valence electrons in a metal are not held tightly to the nuclei of their atoms, but are free to move in the material. That is why metals are good conductors. The valence electrons in insulators, such as glass and rubber, are tightly bound to nuclei of their atoms.

7. Whether a substance is classified as a conductor or insulator depends on how tightly the nuclei of their atoms hold their electrons. Some materials, such as silicon and germanium, are good insulators in their pure crystalline form. But these materials increase in conductivity tremendously when a tiny amount of impurity is added that adds or removes an electron from their crystal structure. This process is called doping. For this reason, silicon and germanium are classified as semiconductors. Semiconductors are used in the manufacturing of transistors, IC’s and diodes.

8. Germanium has 32 protons in its nucleus and 32 electrons orbiting in four energy levels (see Figure ->). The innermost energy level has 2 electrons, the second energy level has 8 electrons, and the third energy level has 18 electrons, and the outer energy level has 4 electrons (valance electrons). Germanium’s outer most level is not stable because this energy level can hold 8 electrons.

9. Silicon has 14 protons in its nucleus and 14 electrons orbiting in three energy levels (see Figure). The innermost energy level has 2 electrons, the second energy level has 8 electrons and the third energy level had 4 electrons (valance electrons).

10. Notice that both germanium and silicon have 4 valence electrons
Notice that both germanium and silicon have 4 valence electrons. Because of this, they are called tetravalent elements. Tetravalent elements will try to assume a stable configuration (8 valence electrons) by forming bonds with adjoining atoms, where they share valence electrons. A cluster of silicon or germanium atoms sharing valence electrons forms a regular arrangement called a crystal. A tetravalent material can be doped with a pentavalent ( 5 valence electrons) material, such as phosphorus, arsenic, or antimony. A phosphorus atom in a cluster of silicon atoms donates an extra electron. This extra electron can move through the crystal with ease. This allows the material to carry an electric charge. A material doped with a pentavalent material is an n-type semiconductor. The “n” stands for “negative” which is the charge resulting from extra electron.

11. If the tetravalent material is doped with a trivalent (3 valence electrons) material, such as boron, a p-type semiconductor is formed. The “p” stand for “positive” which is the charge resulting from a shortage of one electron. A boron atom in a cluster of silicon leaves a vacant electron called a hole. An electron from a nearby atom can move into the hole, thus causing the hole to move to a new location. In a p-type semiconductor the holes carry the electric current. Both n-type and p-type semiconductors conduct electric current. The resistance of both types is determined by the proportion of excess electrons or holes, so both types can function as resistors and can conduct current in any direction.

12. The P-N junction is the interface between a p-type and an n-type material and is the basic design of the unbiased diode, A diode can be forward-biased where it can conduct or reverse-biased where it cannot conduct. When the charge from a battery repels holes toward the P-N junction, electrons will cross the junction and combine with the holes and a current will flow. The diode is then forward-biased. When the charge from the battery attracts holes and electrons away from the P-N junction, no current can flow, The diode is then reversed-biased.

13. Transistors
Transistors are semiconductor devices with three small leads. A very small current or voltage at one lead can control a much larger current flowing through the other two leads. This means that transistors can be used as amplifiers and switches.

14. Transistors make our electronics world go ‘round
Transistors make our electronics world go ‘round. They’re critical as a control source in just about every modern circuit. Sometimes you see them, but more- often-than-not they’re hidden deep within the die of an integrated circuit. In this lesson we’ll introduce you to the basics of the most common transistor around: the bi-polar junction transistor (BJT). A transistor is basically modeled after a pair of P-N junction diodes connected together. These transistors have three divisions or segments: the emitter, the base and the collector. The base is very thin and contains fewer doping atoms than the emitter and collector. Thus a very small emitter-base current will cause a much larger emitter-collector current to flow. Transistors are built by stacking three different layers of semiconductor material together. Some of those layers have extra electrons added to them (a process called “doping”), and others have electrons removed (doped with “holes” – the absence of electrons). A semiconductor material with extra electrons is called an n-type (n for negative because electrons have a negative charge) and a material with electrons removed is called a p-type (for positive). Transistors are created by either stacking an n on top of a p on top of an n, or p over n over p. In both cases, the base ( the middle segment) acts like a gate that controls the current moving through the three parts.

16. Because the emitter-collector current is up to several hundred times greater than the emitter-base current, the transistor acts as a efficient current amplifier. For example, a small current generated by a voice directed towards a microphone is applied to the base of a transistor. The small base current controls the much larger emitter-collector current that is applied to the terminals of a loudspeaker, which emits a greatly amplified sound. It is important to know that in a silicon transistor, the base-emitter junction will not conduct current until the forward voltage exceeds 0.6 volts. It is also important to know that too much current will cause a transistor to become hot and not properly operate correctly. Too much current or voltage can damage or destroy the transistor. The transistors in the MB100 Kit are protected so that they can not be damaged.

17. Integrated Circuits
Integrated circuits (IC’s) are made by forming individual transistors, diodes and resistors on small silicon chips (see Figure below). The components are connected to one another with aluminum “wires” deposited on the chip. Integrated circuits can contain few transistors or they can contain thousands of transistors. One kind of integrated circuit contains over 260,000 transistors on a silicon chip that is only about a quarter-inch square. By 1991, chips with 4 million transistors were being produced and 2011, 3.9 billion transistors in a single IC.

18. Operational Amplifiers
Operational amplifiers (op-amps) are devices which are versatile integrated chips. They are called “operational” because they were originally designed to do mathematical operations. Analog computers use op-amps to solve complex equations. Op-amps are used in applications ranging from monitoring the faint electrical impulses produced by living organisms to comparing the magnitude of two signals and indicating which is larger. Op-amps designed to produce an output voltage that is an amplified but faithful copy of input voltage.

19. Audio- Transformers
Audio-transformers are devices that have the ability to transform voltage and current to higher or lower levels. They are used to match the impedance (opposition to the flow of alternating current) of an amplifier to that of a microphone, speaker or other device. Step-up audio-transformers can be used to increase the power. In either case, the audio-transformer isolates and supplies the output section with a constant load, Audio-transformers are used in intercom systems and televisions sets.