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Semiconductors - Heated Cathode Valves.. Electronics

Semiconductors

It is known that the electrons of an atom move around the nucleus in specific orbits known as energy levels. As for free electrons, they can move from one atom to another, thus forming an electric current. The properties of an element depend on the number of electrons in its outer orbit. For example, the germanium atom contains 32 electrons, four of which are in its outer energy level. Since the electrons of pure germanium are tightly bound to its atom, pure germanium is considered a poor conductor of electricity. It is possible to increase its degree of conductivity by doping it with a small percentage of impurities, such as indium, whose atom contains 49 electrons, three of which are in the outer layer, i.e. one less than what the germanium atom contains.

By doping the germanium crystal with a small percentage of indium, the indium atom shares with three germanium atoms, and one electron remains that can move easily, leaving the germanium atom as if it lacks this electron. This is what is called a positive hole that accepts an electron from another germanium atom (97). As for antimony, its atom contains 51 electrons, five of which are in its outer layer. When the germanium crystal is doped with a small percentage of antimony atoms, the antimony atom shares only four electrons to bond with four germanium atoms, and the fifth electron becomes an excess electron, making it easy to move inside the crystal from one place to another. The above can be summarized in that the crystal that has a deficiency in electrons is characterized by a positive charge, and is called the M-type (positive). The increase in the number of electrons in it creates a negative charge, and in this case it is called the -S (negative) class. In both cases, the movement of electrons or holes produces an electric current.

The diode allows the current to pass quickly in the forward direction as there are a large number of positive holes moving towards the S region and a large number of electrons moving towards the -M region (99). This represents a large current crossing the junction. Semiconductor diodes are made in a way that makes them suitable for the voltage, current and frequency values ​​used (100). As for the point-contact diode, it is made to allow the passage of small currents, but it can operate at very high frequencies.

97 - Germanium and its positive and negative charge carriers.
98 - The MS diode.
99 - The forward and reverse voltage in the diode.

Receiver and amplifier circuits require a DC source.
Germanium rectifiers are used to rectify alternating current, but it has been observed that the temperature of the rectifier rising to 75 m leads to its damage, while the silicon rectifier can withstand a temperature of 200 m. Therefore, it is preferable to use silicon rectifiers at high temperatures. These rectifiers can withstand high-intensity currents of up to several amperes.

100 - Some types of semiconductor diodes.

Semiconductor diodes are widely used in rectifying power supply circuits. They are characterized by their small size, low resistance in forward connection, and ability to withstand high voltages and currents, and do not require separate heating power. It is known that most electronic circuits, including receiver and amplifier circuits, require a direct current source.

Therefore, the alternating current supply is connected to the primary coils of one of the power transformers (101), which isolates all devices from all actual connections with the power source. After that, the voltages can be increased or decreased by choosing an appropriate ratio for the number of turns. The diode allows the current to pass in one direction only. Therefore, it charges one of the charge-storing capacitors. It is also possible to use a diode to rectify the full wave as in valve rectifier circuits to benefit from the full wave of alternating current. Operating the diode connections at the maximum value of the operating current raises their temperature, which is drained by contacting flat plates that radiate the resulting heat. It is possible to connect the diode rectifiers in series or parallel together so that we obtain voltages and currents with values ​​appropriate to the operating conditions. They can also be collected together in special groups (102).

101 - A power rectifier that converts alternating current to direct current.

102 - Stacking and cooling the rectifiers.