Diodes in the glass case. Diodes

We very often use diodes in our circuits, but do you know how it works and what does it represent? Today in the "family" of diodes is not one dozen semiconductor devices, called the "diode." The diode is a small container with evacuated air, inside which, at a short distance from each other, there is an anode and the second electrode is a cathode, one of which has electrical conductivity of type p and the other of which is n.

To imagine how the diode works, let's take for example the situation with the pump inflating the wheel. Here we work as a pump, the air is pumped into the chamber through the nipple, and this air can not go back through the nipple. As a matter of fact air, it is the same electron in a diode, the electronics man has entered, and it is impossible to go back. If suddenly the nipple breaks down that wheel will be blown off, there will be a breakdown of the diode. And if you imagine that the nipple is working, and if we push the pin of the nipple to let the air out of the chamber, and pushing as we like and with what duration it will be a controlled breakdown. From this it can be concluded that the diode transmits current only in one direction (in the opposite direction it also passes, but very small)

The internal resistance of the diode (open) is a non-constant value, it depends on the forward voltage applied to the diode. The greater this voltage, the greater the forward current through the diode, the lower its throughput resistance. One can judge the resistance of a diode by dropping the voltage across it and the current through it. So, for example, if a direct current Ipr passes through the diode. = 100 mA (0.1 A), while the voltage drops 1V, then (according to Ohm's law) the direct resistance of the diode will be: R = 1 / 0,1 = 10 Ohm.

I note at once that we will not go into details and deepen deeply, build graphs, we will not write formulas - we will consider everything superficially. In this article, we will consider a variety of diodes, namely LEDs, zener diodes, varicaps, Schottky diodes, etc.

Diodes

Are indicated on the diagrams like this:

The triangular part is ANOD, and the dash is CATHODE, the anode is plus, the cathode is minus, for example, the diodes are used in power supplies for rectification alternating current, using a diode bridge, you can turn a variable current into a permanent one, they are used to protect different devices from incorrect polarity of switching on, etc.

The diode bridge is 4 diodes that are connected in series, with two diode of the four being turned on, see the pictures below.

This is how the diode bridge is designated, although in some schemes it is denoted by the abbreviated version:

Conclusion ~   connect to the transformer, on the circuit it will look like this:

The diode bridge is designed for conversion, it is often said for rectifying AC to DC. This straightening is called full-wave. The principle of operation of the diode bridge is to pass a positive half-wave of alternating voltage by positive diodes and cut off the negative half-wave by negative diodes. Therefore, a slightly pulsating positive voltage with a constant value is formed at the output of the rectifier.

To ensure that these pulsations were not, put electrolytic capacitors. after the addition of the capacitor, the voltage is slightly increased, but we will not be distracted, you can read about the capacitors.

Diode bridges are used to power radio equipment, are used in power supplies and chargers. As already mentioned, the diode bridge can be made up of four identical diodes, but ready-made diode bridges are also sold, they look like this:

Schottky diodes have a very low voltage drop and have an increased speed compared to conventional diodes.

To put instead of the Schottky diode an ordinary diode is not recommended, a conventional diode can quickly fail. Such a diode is indicated on the diagrams as follows:

Zener

The zener diode prevents the voltage from exceeding a certain threshold on a particular section of the circuit. Can perform both protective and restrictive functions, they work only in circuits direct current. When connecting, observe the polarity. Zener diodes of the same type can be connected in series to increase the stabilized voltage or the formation of a voltage divider.

Zener diodes on circuits are designated as follows:

The main parameter of zener diodes is the stabilization voltage, zener diodes have different stabilization voltages, for example 3v, 5v, 8.2v, 12v, 18v, etc.

Varicap (in a different capacitive diode) changes its resistance, depending on the voltage applied to it. It is used as a controlled capacitor of variable capacity, for example, for tuning high-frequency oscillation circuits.

The thyristor has two stable states: 1) closed, that is, a state of low conductivity, 2) open, that is, a state of high conductivity. In other words, it is capable of transitioning from a closed state to an open state under the action of a signal.

The thyristor has three leads, except for the Anode and Cathode, and also the control electrode, which is used to transfer the thyristor to the switched-on state. Modern imported thyristors are manufactured in the TO-220 and TO-92 buildings.

Thyristors are often used in circuits for power adjustment, for smooth starting of engines or switching on light bulbs. Thyristors allow you to control large currents. For some types of thyristors, the maximum forward current reaches 5000 A or more, and the value of the voltage in the closed state is up to 5 kV. Powerful thyristors of the type T143 (500-16) are used in control cabinets of electric motors, chastotniki.

Triac

The triac is used in systems powered by alternating voltage, it can be represented as two thyristors, which are turned on and off in parallel. The triac passes current in both directions.

Light-emitting diode

The LED emits light when an electric current passes through it. LEDs are used in instrument display devices, in electronic components (optocouplers), cell phones for display and keyboard lighting, powerful LEDs use as a light source in flashlights, etc. LEDs come in different colors, RGB, etc.

Designation on diagrams:

Infrared diode

Infrared LEDs (abbreviated as IR diodes) emit light in the infrared range. Areas of application of infrared LEDs are optical instrumentation, remote control devices, optocouplers, wireless communication lines. Ic diodes are also designated as LEDs.

Infrared diodes emit light outside the visible range, the infrared diode can be seen and looked through, for example, through a cell phone camera, these diodes are also used in CCTV cameras, especially on street cameras so that a picture can be seen in the dark.

Photodiode

The photodiode converts the light to its photosensitive region, in electricity, finds application in the transformation of light into an electrical signal.

Photo diodes (as well as photoresistors, phototransistors) can be compared with solar batteries. Are denoted on the diagrams as follows.

Zener

A diode designed to work in the mode of electric breakdown. Conditional

the graphic designation of the zener diode is shown in Fig. 2.5, a.

Fig. 2.5. Graphical representation of semiconductor diodes:
a) a zener diode; b) Schottky diode; c) Varicap; d) tunnel diode;
e) Inverted diode

In this mode, with a significant change in the zener diode voltage, the voltage varies insignificantly, i.e., the zener diode stabilizes the voltage. The current-voltage characteristic of the Zener diode D814D is shown in Fig. 2.6.

Fig. 2.6. Volt-ampere characteristics

a silicon zener diode D814D

In zener diodes, tunneling, avalanche, and mixed breakdown can occur, depending on the resistivity of the base.
  In zener diodes with low-resistance base (low-voltage, up to 5.7AT) there is a tunnel breakdown, and in the zener diodes with a high resistance base (high-voltage) - avalanche breakdown.

The main parameters of the zener diode are:

1. U  art.  - Stabilization voltage (at a given current in the breakdown mode);

2. I  st.min  - the minimum permissible stabilizing current;

3. I  st.max – the maximum allowable stabilizing current;

4. r  art. –   differential resistance of the zener diode (on the breakdown site),

The values U  art., I  st.min and I  st.max accepted as positive.

For an example of using a zener diode, we turn to the scheme of the so-called parametric voltage regulator (Figure 2.7.). It is easy to see that if the stressu  in  so large that the zener diode is in the breakdown mode, then changes in this voltage practically do not cause a change in voltageu  out (with a change in voltageu  in  only current changesi, as well as tension ).

Fig. 2.7. The scheme of the parametric voltage regulator

The Zener is a high-speed instrument and works well in pulse circuits.

Stabistor

This is a semiconductor diode, the voltage at which direct inclusion  (about 0.7 AT) depends little on the current (the straight branch in the corresponding section is almost vertical). Stabilist is designed to stabilize small voltages.

Schottky Diode

The Schottky diode is not usedp- ntransition, and rectifying contact metal-semiconductor. The conditional graphic designation of the Schottky diode is shown in Fig. 2.5, b.

AT ordinary conditions  The direct current formed by the conduction band electrons, passing from the semiconductor to the metal, is very small. This is a consequence of the lack of electrons, the energy of which would allow them to overcome this barrier.

For increase forward current  it is necessary to "warm up" the electrons in the semiconductor, to raise their energy. Such heating can be carried out by means of an electric field.

If you connect the external voltage source with a plus to the metal, and a minus to the semiconductorntype, the potential barrier will drop and a direct current will flow through the transition. With the opposite connection, the potential barrier increases and the current turns out to be very small.

  Schottky diodes are very fast devices, they can operate at frequencies

up to tens of gigahertz (1 GHz= 1 · 10 9 Hz). A Schottky diode can have a small reverse current and a small

direct voltage (for small direct currents) - about 0.5AT, which is less than for silicon

The total capacity of the diode at the minimum characteristic point is 0.8 ... 1.9 pF. It is useful to note that the test of the diode is not allowed by the tester. Tunnel diodes can operate at very high frequencies - more than 1 GHz.

The presence of a section with a negative differential resistance on the current-voltage characteristic provides the possibility of using tunnel diodes as an amplifying element and as the main element of the generators.

At present, tunnel diodes are used precisely in this capacity in the region of ultrahigh frequencies.

Reversed diode

This is a semiconductor diode, the physical phenomena in which are similar to physical phenomena in a tunnel diode, so the reversed diode is often considered as a variant of a tunnel diode. In this case, a section with a negative differential resistance on the current-voltage characteristic of the reversed diode is absent or very weakly expressed.

The reverse branch of the current-voltage characteristic of the reversed diode (which is characterized by a very small voltage drop) is used as a straight branch of the "ordinary diode", and the straight branch is used as the reverse branch. Hence the name - the reversed diode.

The conditional graphic designation of the reversed diode is shown in Fig. 2.5, d.

As an example, consider the current-voltage characteristics of a germanium inverted diode 1I104A (Figure 2.9), intended, among other things, for operation in impulse devices (direct direct current - not more than 0.3 mA, constant reverse current - no more than 4 mA  (with ), the total capacitance at the minimum of the current-voltage characteristic 1.2 ... 1.5 pF).

As can be seen from the graph (Fig. 2.9), both branches of the current-voltage characteristic are practically symmetrical (in specular reflection) relative to the origin. The negative differential resistance section is located in the positive voltage section between 0.1 and 0.3 AT. In this case, the amplitude of the current in the section with negative differential resistance does not exceed 0.05 mA.

Fig. 2.9. Volt-ampere characteristic of the reversed diode.

The standard design of a semiconductor diode is made in the form of a semiconductor device. It has two terminals and one rectifying electrical transition. The device uses various properties associated with electrical transitions. The whole system is connected in a single body made of plastic, glass, metal or ceramic. A part of a crystal with a higher impurity concentration is called an emitter, and a region having a low concentration is called a base. In accordance with the individual properties and constructive features, the diodes are marked, reflecting their technical characteristics.

Characteristics and parameters of diodes

Depending on the material used, the diodes can be made of silicon or germanium. In addition, indium phosphide and gallium arsenide are used for their production. Diodes from germanium have a higher transmission factor, compared with silicon products. They have a high conductivity with relatively low voltage. Therefore, they are widely used in the manufacture of transistor receivers.

Depending on the technological features and design, the diodes are planar or point, impulse, universal or rectifier. Among them, it should be noted a separate group, which includes, photodiodes and thyristors.

The characteristics of diodes are determined by such parameters as forward and reverse currents and voltages, temperature ranges, maximum reverse voltage and other values. Depending on this, the appropriate designations are made.

Designations and color marking of diodes

Modern designations of diodes meet new standards. They are divided into groups, depending on the limiting frequency at which the current transfer increases. Therefore, diodes are low, medium, high and ultra-high frequency. In addition, they have different dissipated power: small, medium and large.

The marking of the diodes must take into account the parameters and technical features of the conductor. The material from which the semiconductor is made is indicated on the body by corresponding letter symbols. These designations shall be affixed together with the purpose, type, electrical properties of the instrument and its symbol. This helps, in the future, to properly connect the diode to the electronic circuitry  device. The anode and cathode terminals are indicated by an arrow or signs plus or minus. Color codes and marks in the form of dots or strips are applied near the anode. All designations and color markings allow you to quickly determine the type of device and use it correctly in various schemes.

Marking of imported diodes

Diode   is a two-electrode semiconductor device. It is accordingly Anode  (+) or positive electrode and Cathode (-) or negative electrode. It is customarily said that the diode has (p) and (n) regions, they are connected to the diode terminals. Together they form a p-n junction. Let us examine in more detail, what is this p-n junction. The semiconductor diode is a purified silicon or germanium crystal in which an acceptor impurity is introduced into the region (p), and a donor impurity is introduced into the region (n). As a donor impurity ions can act Arsenic, and as an acceptor impurity ions India. The main property of the diode is the ability to pass current only in one direction. Consider the following figure:

This figure shows that if the diode is switched on Anode  to the plus of food and Cathodic  to the minus supply, the diode is in the open state and conducts the current, since its resistance is negligible. If the diode is on Anode  to minus, and Cathodic  to plus, then the resistance of the diode will be very large, and there will be practically no current in the circuit, or rather it will be, but so small that it can be neglected.

More details can be obtained by looking at the following graph, Volt-Ampere characteristic of the diode:

In the direct connection, as we see from this diagram, the diode has little resistance, and accordingly it passes the current well, and in the reverse switching to a certain voltage value the diode is closed, has a large resistance and practically does not conduct current. This is easy to see if there is a diode and a multimeter near the hand, you need to put the device in the position of an audible dial, or by setting the multimeter switch opposite the diode icon, in the extreme case, you can try calling the diode by setting the switch to the position of 2 kΩ resistance measurement. It is depicted in the circuit diagrams of the diode as in the figure below, remember where the conclusion is easy: the current is known to always flow from plus to minus, so the triangle in the diode image seems to show its current direction, that is, from plus to the minus.

By connecting the red test lead of the multimeter to the Anode, we can verify that the diode passes the current in the forward direction, on the screen of the instrument there will be numbers equal to ~ 800-900 or close to it. Having connected the probes on the contrary, the black probe to the anode, red to the cathode, we see on the screen unit, which confirms that in the reverse switching the diode does not pass current. The diodes considered above are plane and point diodes. Planar diodes are designed for medium and high power and use them mainly in rectifiers. Point diodes are designed for low power and are used in detectors of radio receivers, can operate at high frequencies.

Planar and point diode

What are the types of diodes?

A) The photo shows the above diode.

B) This picture shows zener diode, (the foreign name is the diode of Zener), it is used when the diode is turned on again. The main goal: keeping the voltage stable.

Dual-mode zener diode - the image on the diagram

AT) Two-sided  (or two-way) zener diode. Plus this zener diode is that it can be switched on regardless of the polarity.

D) can be used as an amplifying element.

D), is used in high-frequency circuits for detection.

E), is used as a capacitor of variable capacity.

G), when the device is illuminated in a circuit connected to it, a current arises due to the formation of pairs of electrons and holes.

H), all known, and probably the most widely used devices, after conventional rectifying diodes. They are used in many electronic devices for indication and not only.

Rectifier diodes   are also available in the form of diode bridges, we will analyze what it is - four diodes connected in one body to receive a constant (rectified) current. They are connected by Bridge scheme, standard for rectifiers:

They have four marked outputs: two for connecting AC, and plus with a minus. The photo shows a diode bridge KC405:

And now let's consider in more detail the field of application of LEDs. LEDs (or rather lED lamp) are manufactured by the industry and for lighting the premises, as an economical and durable light source, with a cap allowing them to be screwed into a regular cartridge for incandescent lamps.

LED Photo Lamp

LEDs exist in different buildings, including SMD.

The so-called RGB LEDs are also available, inside of them there are three crystals of LEDs with different Red-Green-Blue glows respectively Red - Green - Blue, these LEDs have four outputs and allow any color to be visible by mixing colors.

These SMD LEDs are often available in the form of tapes with already installed resistors and allow them to be connected directly to a 12 volt power supply. You can use a special controller to create lighting effects:

Rgb controller

When used, they do not like when they are supplied with a supply voltage higher than that for which they are designed and can burn out immediately or after a while, so the voltage of the power supply must be calculated by the formulas. For Soviet LEDs like AL-307, the supply voltage should be approximately 2 volts, for imported 2-2.5 volts, naturally with current limitation. For food lED strip light, if no special controller is used, a stabilized power supply is necessary. Material prepared - AKV.

Discuss the article DIODES

A diode is usually understood as an electrovacuum or semiconductor device that passes an alternating electric current in only one direction and has two contacts for inclusion in electrical circuit. The unidirectional conductivity of a diode is its main property. This property and determines the purpose of the diode:

• conversion of high-frequency modulated oscillations to audio frequency currents (detection);
• rectification of alternating current into a constant.

Detection is also understood as signal detection.

Classification of diodes

According to the initial semiconductor material, the diodes are divided into four groups:

• germanium,
• silicon,
• from gallium arsenide,
• from indium phosphide.

Germanium diodes  widely used in transistor receivers, since they have a higher transmission factor than silicon.

This is due to their greater conductivity at a small voltage (about 0.1 ... 0.2 V) of the high-frequency signal at the detector input and the relatively low load resistance (5 ... 30 kOhm).

According to the structural and technological features  distinguish diodes:

• point,
• planar.

By appointment semiconductor diodes  are divided into the following main groups:

• rectifying,
• universal,
• pulse,
• varicaps,
• zener diodes (reference diodes),
• stabilizers,
• tunnel diodes,
• reversed diodes,
• avalanche-passing (LAP),
• thyristors,
• photodiodes, s
• lEDs and optocouplers.

Diodes are characterized by such basic electrical parameters:

• current flowing through the diode in the forward direction (direct current Ipr);
• current flowing through the diode in the opposite direction (reverse current Ipep);
• the largest permissible rectified TOKOM Іvpr.maks;
• the highest permissible direct current of the Ip.d.
• direct voltage Unp;
• reverse voltage and;
• maximum allowable reverse voltage
• capacitance SD between the terminals of the diode;
• dimensions and operating temperature range.

The old notation system

In accordance with the notation system developed before 1964, the abbreviated designation of diodes consisted of two or three elements.

The first element  alphabetic, D - diode.

The second element  - number corresponding to the type of the diode: 1 ... 100 - point germanium, 101 ... 200 -point silicon, 201 ... 300 - planar silicon, 801 ... 900 - zener diodes, 901 ... 950 - varicaps, 1001 ... 1100 - straightening poles. The third element  - a letter indicating the version of the device. This element may be absent if there are no diode species.

Currently  there is a system of designations corresponding to GOST 10862-72. In the new, as in the old system, the following division into groups according to the limiting (boundary) frequency of amplification (current transmission) is adopted:

• low-frequency LF (up to 3 MHz),
• the average frequency of the midrange (from 3 to 30 MHz),
• high-frequency HF (over 30 MHz),
• ultrahigh-frequency microwave;

By power dissipation:

• low-power (up to 0.3 W),
• average power (from 0.3 to 1.5 W),
• large (over 1.5 W) power.

The new notation system

New system for marking diodes  more perfect. It consists of four elements.

The first element  (letter or number) indicates the initial semiconductor material from which the diode was made: G or 1 - germanium  * К or 2 - silicon  , A or 3 - gallium arsenide , And or 4 - indium phosphide.

The second element  - a letter indicating the class or group of the diode.

The third element  - the number that determines the purpose or electrical properties of the diode.

The fourth element  indicates the ordinal number of the technological development of the diode and is denoted from A to Z.

For example:

• the diode KD202A is deciphered: K - material, silicon, D - rectifier diode, 202 - designation and development number, A - variety;
• 2C920 - a high power silicon zener diode of type A;
• AI301B - arsenide gallium tunnel diode switching type B.

Sometimes there are diodes, indicated by obsolete systems: DG-C21, D7A, D226B, D18. Diodes D7 differ from the DG-C diodes by the all-metal construction of the case, as a result of which they work reliably in a humid atmosphere.

Germanium diodes such as DG-C21 ... DG-Ts27 and close to them D7A ... D7Z diodes are usually used in rectifiers for powering radio equipment from an alternating current network.

The symbol for the diode does not always include some technical data, so they need to be found in the reference books on semiconductor devices.

One of the exceptions is the designation for some diodes with letters KC or a figure instead of K (for example, 2C) - silicon zener diodes and stabilizers.

After these designations there are three digits, if they are the first digits: 1 or 4, then taking the last two digits and dividing them by 10 we get the stabilization voltage Ust.

For example:

• KS107A - a stabilizer, Ust = 0,7 V,
• 2С133А - a stabilitron, Ust = 3,3 V.

If the first digit is 2 or 5, then the last two digits indicate Ust, for example:

• KS 213B - Ust = 13 V,
• 2C 291A - Ust = 91 V.

If the digit is 6, then to the last two digits you need to add 100 V, for example: KS 680A - Ust = 180 V.

Marking of diodes

The semiconductor material is usually indicated on the diode body, from which it is made (letter or figure), type (letter), purpose or electrical properties of the device (figure), the letter corresponding to the version of the device, and the date of manufacture, as well as its symbol.

The symbol for the diode (anode and cathode) indicates how to connect the diode on the device boards. The diode has two leads, one of which is a cathode (minus), and the other is an anode (plus).

A conditional graphic image on the diode body is applied in the form of an arrow indicating direct direction, if there is no arrow, then the "+" sign is placed.

On the flat terminals of some diodes (for example, the D2 series), the conventional designation of the diode and its type are directly stamped. When applying the color code, the color mark, dot or strip is applied closer to the anode (Figure 1).

For some types of diodes, color marking in the form of dots and strips is used (Table 1). Diodes of old types, in particular point ones, were produced in glass design and were marked with the letter "D" with the addition of a number and a letter denoting the device subtype. The germanium-indium planar diodes had the designation "D7".

Fig. 1. Apply color code to diodes.

Table 1 Color marking  semiconductor diodes.

Diode type	The color of the ring (k), the point (m)
	from the side of the cathode (in the middle of the shell)	anode side
		Orange t Blue t. Green t. Black t. Red t.
	Red t. Orange t. Yellow t. Blue t. Green and blue t. Two yellow t. Two white t. Two green t.	Red t.
	Yellow t. Orange t.	Green t.
		Yellow t.
	White or yellow strip on the front of the case	Green t. Red t. White or yellow t.
	Label black, green or yellow	Black t. Green t.

* The color of the case is brown.

Diode type	The color of the ring (k), the point (m)
	from the side of the cathode (in the middle of the shell)	anode side
		Orange to. The Red Square. Green to. Yellow c. Blue to.
KD243ZH	Purple to. Orange to. The Red Square. Green to. Yellow c. Blue to.
KD510A	One wide and two narrow green to.
2D510A	One wide and one narrow green to.
KD521A		1 wide + 2 narrow
KD521B		Blue Stripes
KD521V		Yellow stripes
KD522A	One narrow black to.	One broad
KD522B	Two narrow black k.	Black ring
KD522B	Three narrow black k.	+ type of diode

Literature: V.M. Pestrikov. Encyclopedia of radio amateurs.