Diodes and Zener diode

Semiconductor devices designed to regulate the direction of current, i.e. Diodes allow current to flow in one direction, but not in the other. The element in the diagram is indicated in the form of a triangle, the vertex of which indicates the direction of current flow. A vertical line is depicted in front of the vertex, which indicates that this is the CATHODE (-) of the diode, and the opposite side is its ANODE (+).
Рис 13. Устрйоство диода.jpeg
Рис 13. Устрйоство диода.jpeg

BAX diode

If we look at the BAX (volt-ampere characteristic) of the diode, we see that it already has a negative shoulder, where the current moves in the opposite direction. The following characteristics exist for rectifier diodes.
Vr - maximum diode reverse voltage
If - average diode current
Ifsm - maximum pulse current
Ir - average reverse current
Vf - average forward voltage of the diode
Diode differential resistance
Pd - average power dissipation

Diodes come in different packages, but the most common are DO-41 (DO204) for rectifier diodes, these are the classic two solder contacts that are inserted into the board. There can also be power diodes, which are attached to a thread with the anode, which gives good contact and the possibility of use at high currents.
Резистор и стабилтрон.jpg

History of the invention of the diode

Diode from Greek means Di (two) and od (electrode) - a two-electrode electronic component. The diode, as we see, has an asymmetrical and nonlinear current-voltage characteristic.

The first diodes appeared back in the 19th century and were based on a vacuum lamp, inside of which an electrode (anode) was placed and voltage was applied to it, some of the electrons were separated into a vacuum and fell on the cathode located on the opposite side, then these elements were improved by adding a grid between cathode and anode, capable of regulating the number of transmitted electrons due to the applied voltage. Later, the first crystal diodes appeared, on their basis radio receivers were made, which were called transistors
Рис 14. Разновидности диодов.jpeg

pn junction

Semiconductors (such as diodes) are located between conductors and dielectrics. p - positive (positive), n-negative (negative) Semiconductors include germanium, silicon, etc. Depending on the added impurity we get either an N or P element. So if we add arsenic, which has 5 electrons in its outer orbit, and silicon has 4, we get an extra electron, and N-type, at the same time, if we add a substance with 3 electrons (indium), we get a HOLE - an empty space under an electron. If we connect P and N, we get a diode with a PN junction.
Depending on the material (silicon or germanium), the forward voltage drop will change, so for silicon diodes it is 0.7 v and for germanium diodes 0.3 v

Zener diode

Zener diodes can be in a glass case, either marked with letters and numbers, or with color rings, like resistors. One of the most popular SMD zener diode packages SOD-80

The principle of operation of a zener diode was first described by the American scientist Zener, for which these semiconductor diodes were called Zener diodes or Zener diodes. The main characteristic of this diode is the current-voltage characteristic presented below. Zener diodes are used to obtain a constant voltage in individual sections of the circuit, for example, to stabilize the output voltage

As can be seen from the graphs, the resistor has linear characteristics and a relationship between voltage and current, unlike a zener diode which has a complex curve showing that at a certain voltage, changing the current does not affect its graph, but when a certain voltage value is reached, the diode opens.

In the diagram, the zener diode is indicated in the form of a triangle resting on a perpendicular line, just like the diode, but unlike the diode, the zener diode has a tail on the designation showing this difference; the location of the anode and cathode is very clearly visible in the diagram
Стабилитрон на схеме.jpg

Light-emitting diode

One of the diodes that everyone has seen is an LED; it is perhaps impossible to imagine a single home where the red diode is not on. The radiation occurs at a certain wavelength, which characterizes the color of the diode; the most popular color is, of course, red, but blue and green and many others are also found.

The LED also has two contacts: Anode - Long lead, and Cathode - short contact and a bevel on the body; to connect the LED from a DC circuit, you need a current-limiting resistor, which we will do a little later.
Рис 15. Светодиод в LCR метре.jpeg

Connecting an LED to a circuit

After we talked about the resistor, diode and buttons, it's time to make our first circuit, in the counter we will combine all these elements to make the LED glow, but first let's look at the current-voltage characteristic of the diode. As we see, diodes of different colors have different BAX, but this is not important to us here, but that at voltages up to 1.6 volts for a red LED (RED LED), we do not consume current, which means the diode does not light up if we raise the voltage to 1.8 volts, then the diode is already burning, but not brightly; the higher the voltage, the brighter the diode will burn and the higher the current will become.

Most radio components have datasheets, this is technical documentation that the manufacturer prepares regarding testing and their own research, in relation to our diode, to find the datasheet we google “Led Red DataSheet PDF”, open it and see the maximum current of 20 milliAmps (mA) or 0.02 Ampere.
If we plan to power our diode using 5 volts, then we also need to look at the operating voltage

5V- 3.2V (operating voltage) = 1.8 volts
R=1.8 volts / 0.02 Amperes = 90 Ohms
The nearest higher value is 120 Ohms (it is better to take a larger resistor to reduce the current and extend the life of the diode)
Токоограничивающий резистор для светодиода.jpg

Tunnel diodes

Another example of using dynamic, i.e. variable resistance in semiconductors are tunnel diodes; its current-voltage characteristic is shown in the figure. At points between A and B, the tunnel diode has a negative dynamic resistance, which means that during this period the voltage divider consisting of a tunnel diode and a resistor works as an amplifier.

In the 50s, great hopes were placed on tunnel diodes, since their high performance gave hope for a breakthrough in the field of computer technology, but as we know, history does not tolerate subjunctive moods and the advent of transistors pushed these hopes into the far corner. But the phenomenon of negative resistance is important for further understanding of topics such as active filters and negative impedance converter
Туннельный диод.jpg
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