- the simplest semiconductor devices, the basis of which is the electron-hole transition ( pn junction). As is known, the main property of a p-n junction is one-way conductivity: from region p (anode) to region n (cathode). This is also clearly conveyed by the conventional graphic symbol of a semiconductor diode: a triangle (symbol of the anode), together with the electrical connection line crossing it, forms something like an arrow indicating the direction of conduction. The dash perpendicular to this arrow symbolizes the cathode ( rice. 7.1).
The letter code of the diodes is VD. This code denotes not only individual diodes, but also entire groups, for example, rectifying poles. The exception is a single-phase rectifier bridge, depicted as a square with the corresponding number of terminals and a diode symbol inside ( rice. 7.2, VD1). The polarity of the voltage rectified by the bridge is not indicated on the diagrams, since it is clearly determined by the diode symbol. Single-phase bridges, structurally combined in one housing, are depicted separately, indicating that they belong to one product in the position designation (see. rice. 7.2, VD2.1, VD2.2). Next to the position designation of the diode, you can also indicate its type.
On the basis of the basic symbol, graphic symbols for semiconductor diodes with special properties are also constructed. To show on the diagram zener diode, the cathode is supplemented with a short stroke directed towards the anode symbol ( rice. 7.3, VD1). It should be noted that the location of the stroke relative to the anode symbol should be unchanged regardless of the position of the zener diode UGO in the diagram (VD2-VD4). This also applies to the symbol of a two-anode (double-sided) zener diode (VD5).
Conventional graphic symbols are constructed in a similar way tunnel diodes, reversed and Schottky diodes — semiconductor devices, used for signal processing in the microwave region. In the tunnel diode symbol (see Fig. 7.3 , VD8) the cathode is supplemented with two strokes directed in one direction (towards the anode), in the UGO of the Schottky diode (VD10) - in different directions; in the UGO of the reversed diode (VD9) - both lines touch the cathode with their middle.
The property of a reverse-biased p-n junction to behave like an electrical capacitance is used in special diodes - varicapah(from words vari(able)- variable and cap(acitor)- capacitor). Conditional graphic designation of these devices clearly reflects their purpose ( rice. 7.3, VD6): two parallel lines are perceived as a capacitor symbol. Like variable capacitors, for convenience, varicaps are often manufactured in the form of blocks (they are called matrices) with a common cathode and separate anodes. For example in Fig. Figure 7.3 shows the UGO of a matrix of two varicaps (VD7).
The basic diode symbol is also used in the UGO thyristors(from Greek Thyra- door and English resistor- resistor) - semiconductor devices with three p-l junctions ( p-n-p-n structure), used as switching diodes. The letter code of these devices is VS.
Thyristors with leads only from the outermost layers of the structure are called dinistors and is designated by a diode symbol, crossed out by a line segment parallel to the cathode ( rice. 7.4, VS1). The same technique was used when constructing the UGO symmetrical dinistor(VS2), conducting current (after it is turned on) in both directions. Thyristors with an additional, third output (from one of the internal layers of the structure) are called thyristors. Control along the cathode in the UGO of these devices is shown by a broken line attached to the cathode symbol (VS3), along the anode - by a line extending one of the sides of the triangle symbolizing the anode (VS4). The graphic designation of a symmetrical (bidirectional) SCR is obtained from the symbol of a symmetrical dinistor by adding third output (see Fig.7.4, VS5).
Of the diodes that change their parameters under the influence of external factors, the most widely used photodiodes. To show such a semiconductor device in a diagram, the basic diode symbol is placed in a circle, and next to it (at the top left, regardless of the position of the UGO) a photoelectric effect sign is placed - two oblique parallel arrows directed towards the symbol ( rice. 7.5, VD1—VD3). The UGO of any other semiconductor diode controlled by optical radiation is constructed in a similar way. On rice. 7.5 As an example, the conventional graphic designation of photodinistor VD4 is shown.
Conventional graphic symbols are constructed in a similar way light emitting diodes, but arrows indicating optical radiation are placed at the top right, regardless of the position of the UGO and are directed in the opposite direction ( rice. 7.6). Since LEDs emitting visible light are usually used as indicators, they are designated in diagrams by the Latin letters HL. The standard letter code D is used only for infrared (IR) LEDs.
LED character indicators are often used to display numbers, letters and other characters. Conventional graphic symbols for such devices are not formally provided for in GOST, but in practice symbols like HL3, shown in rice. 7.6, which shows the UGO of a seven-segment indicator for displaying numbers and a comma. Segments of such indicators are designated lowercase letters Latin alphabet clockwise, starting from the top. This symbol clearly reflects the almost real arrangement of light-emitting elements (segments) in the indicator, although it is not without a drawback; it does not carry information about the polarity of inclusion in the electrical circuit (since similar indicators are produced with both a common anode and a common cathode, the connection patterns will differ). However, this does not cause any particular difficulties, since the connection of the common terminal of the indicators is usually indicated on the diagram. The letter code of the sign indicators is HG.
Light-emitting crystals are widely used in optocouplers - special devices used to connect individual parts electronic devices in cases where their galvanic isolation is necessary. In the diagrams, optocouplers are designated by the letter U and depicted as shown in rice. 7.7.
The optical connection of the emitter (LED) and the photodetector is shown in this case by two arrows perpendicular to the electrical communication lines - the outputs of the optocoupler. The photodetector in the optocoupler can be a photodiode (see. rice. 7.7, U1), photothyristor U2, photoresistor U3, etc. The relative orientation of the symbols of the emitter and photodetector is not regulated. If necessary, the components of the optocoupler can be depicted separately, but in this case, the optical connection sign should be replaced with the signs of optical radiation and photoelectric effect, and the belonging of the parts to one product should be shown in the position designation (see. rice. 7.7, U4.1, U4.2).
In this article we will show a table of graphic symbols of radio elements in the diagram.
A person who does not know the graphic designation of the elements of a radio circuit will never be able to “read” it. This material is intended to give the novice radio amateur where to start. Such material is found very rarely in various technical publications. This is precisely why he is valuable. In different publications there are “deviations” from the state standard (GOST) in the graphic designation of elements. This difference is important only for state acceptance authorities, but for a radio amateur it has no practical significance, as long as the type, purpose and main characteristics of the elements are clear. Besides, in different countries and the designation may be different. Therefore, this article provides different options for graphically designating elements on a diagram (board). It may well be that you will not see all designation options here.
Any element on the diagram has a graphic image and its alphanumeric designation. The shape and dimensions of the graphic designation are determined by GOST, but as I wrote earlier, they have no practical significance for a radio amateur. After all, if on the diagram the image of the resistor is smaller in size than according to GOST standards, the radio amateur will not confuse it with another element. Any element is indicated on the diagram by one or two letters (the first one must be capitalized), and by a serial number on a specific diagram. For example, R25 means that it is a resistor (R), and in the diagram shown it is the 25th in a row. Sequence numbers are typically assigned from top to bottom and left to right. It happens that when there are no more than two dozen elements, they are simply not numbered. It happens that when modifying circuits, some elements with a “large” serial number may be in the wrong place in the circuit; according to GOST, this is a violation. Obviously, the factory acceptance was bribed with a bribe in the form of a banal chocolate bar, or an unusually shaped bottle of cheap cognac. If the circuit is large, then it can be difficult to find elements that are out of order. With a modular (block) construction of equipment, the elements of each block have their own serial numbers. Below you can find a table containing designations and descriptions of the main radio elements; for convenience, at the end of the article there is a link to download the table in WORD format.
Table of graphic designations of radioelements on the diagram
| Graphic designation (options) | Item name | Brief description of the item |
| Battery | Single source of electrical current, including: watch batteries; AA salt batteries; dry batteries; cell phone batteries | |
 | Battery | A set of single elements designed to power equipment with an increased total voltage (different from the voltage of a single element), including: batteries of dry galvanic batteries; rechargeable batteries dry, acidic and alkaline elements |
| Knot | Connection of conductors. The absence of a dot (circle) indicates that the conductors in the diagram intersect, but do not connect to each other - these are different conductors. Does not have an alphanumeric designation | |
 | Contact | A terminal of a radio circuit intended for “rigid” (usually screw) connection of conductors to it. Most often used in large power management and control systems of complex multi-unit electrical circuits |
 | Nest | Connecting easily removable contact of the “connector” type (in amateur radio slang - “mother”). Used primarily for short-term, easily disconnected connections of external devices, jumpers and other circuit elements, for example as a test socket |
| Socket | A panel consisting of several (at least 2) female contacts. Designed for multi-contact connection of radio equipment. A typical example is a 220V household electrical outlet. | |
| Plug | Contact easily removable pin contact (in the slang of radio amateurs - “dad”), intended for short-term connection to a section of an electrical radio circuit | |
 | Fork | Multi-pin connector, with a number of contacts of at least two, intended for multi-pin connection of radio equipment. A typical example is the power plug of a 220V household appliance. |
| Switch | A two-contact device designed to close (open) an electrical circuit. A typical example is a “220V” light switch in a room | |
 | Switch | A three-contact device designed to switch electrical circuits. One contact has two possible positions |
 | Tumblr | Two “paired” switches - switched simultaneously by one common handle. Separate groups of contacts can be depicted in different parts of the diagram, then they can be designated as group S1.1 and group S1.2. In addition, if there is a large distance in the diagram, they can be connected by one dotted line |
 | Galetny switch | A switch in which one "slide" type contact can be switched to several different positions. There are paired biscuit switches, in which there are several groups of contacts |
 | Button | A two-contact device designed to briefly close (open) an electrical circuit by pressing it. A typical example is a button doorbell apartments |
| Common wire (GND) | A contact of a radio circuit that has a conditional “zero” potential relative to other sections and connections of the circuit. Typically, this is the output of the circuit, the potential of which is either the most negative relative to the rest of the circuit (minus the circuit's power supply) or the most positive (plus the circuit's power supply). Does not have an alphanumeric designation | |
| Grounding | The pin of the circuit to be connected to Earth. Allows you to exclude possible appearance harmful static electricity, and also prevents electric shock in the event of possible contact with dangerous voltage on the surfaces of radio devices and units that are touched by a person standing on wet ground. Does not have an alphanumeric designation | |
 | Incandescent lamp | An electrical device used for lighting. Under the influence of electric current, the tungsten filament glows (it burns). The filament does not burn out because there is no chemical oxidizing agent - oxygen - inside the lamp bulb |
 | Signal lamp | A lamp designed to monitor (signal) the status of various circuits of outdated equipment. Currently, instead of signal lamps, LEDs are used, which consume lower current and are more reliable. |
 | Neon lamp | Gas discharge lamp filled with inert gas. The color of the glow depends on the type of filler gas: neon – red-orange, helium – blue, argon – lilac, krypton – blue-white. Other methods are also used to give a certain color to a lamp filled with neon - the use of luminescent coatings (green and red glow) |
 | Fluorescent lamp (LDS) | Gas discharge lamp, including a miniature bulb energy saving lamp, using a luminescent coating - a chemical composition with an afterglow. Used for lighting. With the same power consumption, it produces brighter light than an incandescent lamp |
 | Electromagnetic relay | An electrical device designed to switch electrical circuits by applying voltage to the electrical winding (solenoid) of a relay. A relay can have several groups of contacts, then these groups are numbered (for example P1.1, P1.2) |
 | An electrical device designed to measure the strength of electric current. It consists of a fixed permanent magnet and a movable magnetic frame (coil) on which the arrow is attached. The greater the current flowing through the frame winding, the greater the angle the arrow deflects. Ammeters are divided according to the rated current of the full deflection of the pointer, by accuracy class and by area of application | |
 | An electrical device designed to measure the voltage of an electric current. In fact, it is no different from an ammeter, since it is made from an ammeter by being connected in series to an electrical circuit through an additional resistor. Voltmeters are divided according to the rated voltage of the full deflection of the pointer, by accuracy class and by area of application | |
 | Resistor | A radio device designed to reduce the current flowing through an electrical circuit. The diagram indicates the resistance value of the resistor. The power dissipation of the resistor is depicted by special stripes, or Roman symbols on graphic representation housing depending on the power (0.125W – two oblique lines “//”, 0.25 – one oblique line “/”, 0.5 – one line along the resistor “-“, 1W – one transverse line “I”, 2W – two transverse lines “II”, 5W – tick “V”, 7W – tick and two transverse lines “VII”, 10W – crosshair “X”, etc.). The Americans have a zigzag designation for the resistor, as shown in the figure. |
| Variable resistor | A resistor whose resistance at its central terminal is adjusted using a “knob.” The nominal resistance indicated in the diagram is the total resistance of the resistor between its extreme terminals, which is not adjustable. Variable resistors can be paired (2 on one regulator) | |
| Trimmer resistor | A resistor, the resistance of which at its central terminal is adjusted using a “regulator slot” - a hole for a screwdriver. Like a variable resistor, the nominal resistance shown in the diagram is the total resistance of the resistor between its outer terminals, which is not adjustable | |
| Thermistor | A semiconductor resistor whose resistance changes depending on the ambient temperature. As the temperature increases, the resistance of the thermistor decreases, and as the temperature decreases, on the contrary, it increases. It is used to measure temperature as a temperature sensor, in thermal stabilization circuits of various equipment cascades, etc. | |
| Photoresistor | A resistor whose resistance changes depending on the light level. As the illumination increases, the resistance of the thermistor decreases, and when the illumination decreases, on the contrary, it increases. Used for measuring illumination, recording light fluctuations, etc. A typical example is the “light barrier” of a turnstile. Recently, instead of photoresistors, photodiodes and phototransistors are more often used | |
 | Varistor | A semiconductor resistor that sharply reduces its resistance when the voltage applied to it reaches a certain threshold. Varistor is designed to protect electrical circuits and radio devices from random voltage surges |
 | Capacitor | An element of a radio circuit that has an electrical capacitance and is capable of accumulating an electrical charge on its plates. The application is varied depending on the size of the capacitance; the most common radio element after the resistor |
 | A capacitor, in the manufacture of which an electrolyte is used, due to this, with a relatively small size, has a much larger capacity than an ordinary “non-polar” capacitor. When using it, polarity must be observed, otherwise the electrolytic capacitor loses its storage properties. Used in power filters, as pass-through and storage capacitors for low-frequency and pulse equipment. A conventional electrolytic capacitor self-discharges in no more than a minute, has the property of “losing” capacity due to the drying out of the electrolyte; to eliminate the effects of self-discharge and loss of capacity, more expensive capacitors are used - tantalum | |
| A capacitor whose capacity is adjusted using a “regulator slot” - a hole for a screwdriver. Used in high frequency circuits of radio equipment | ||
| A capacitor whose capacity is adjusted using a handle (steering wheel) located outside the radio receiver. Used in high-frequency circuits of radio equipment as an element of a selective circuit that changes the tuning frequency of a radio transmitter or radio receiver | ||
| A high-frequency device that has resonant properties similar to an oscillatory circuit, but at a certain fixed frequency. Can be used at “harmonics” - frequencies that are multiples of the resonant frequency indicated on the device body. Often, quartz glass is used as a resonating element, so the resonator is called a “quartz resonator”, or simply “quartz”. It is used in generators of harmonic (sinusoidal) signals, clock generators, narrow-band frequency filters, etc. | ||
 | Winding (coil) made of copper wire. It can be frameless, on a frame, or can be made using a magnetic core (a core made of magnetic material). Has the property of storing energy due to magnetic field. Used as an element of high-frequency circuits, frequency filters and even the antenna of a receiving device | |
 | A coil with adjustable inductance, which has a movable core made of magnetic (ferromagnetic) material. As a rule, it swings on a cylindrical frame. Using a non-magnetic screwdriver, the depth of immersion of the core into the center of the coil is adjusted, thereby changing its inductance | |
 | An inductor containing a large number of turns, which is performed using a magnetic circuit (core). Like a high-frequency inductor, the inductor has the property of storing energy. Used as audio low-pass filter elements, power supply and pulse accumulation filter circuits | |
| An inductive element consisting of two or more windings. An alternating (changing) electric current applied to the primary winding causes a magnetic field to appear in the transformer core, which in turn induces magnetic induction in the secondary winding. As a result, an electric current appears at the output of the secondary winding. The dots on the graphic symbol at the edges of the transformer windings indicate the beginnings of these windings, Roman numerals indicate the winding numbers (primary, secondary) | ||
 | A semiconductor device capable of passing current in one direction but not in the other. The direction of the current can be determined by a schematic diagram - converging lines, like an arrow, indicate the direction of the current. The anode and cathode terminals are not indicated by letters in the diagram. | |
 | A special semiconductor diode designed to stabilize the voltage of reverse polarity applied to its terminals (for a stabistor - straight polarity) | |
| A special semiconductor diode that has an internal capacitance and changes its value depending on the amplitude of the reverse polarity voltage applied to its terminals. It is used to generate a frequency-modulated radio signal in circuits for electronic regulation of the frequency characteristics of radio receivers | ||
 | A special semiconductor diode, the crystal of which glows under the influence of an applied direct current. Used as a signal element for the presence of electric current in a certain circuit. Comes in different glow colors | |
| A special semiconductor diode, when illuminated, a weak electric current appears at the terminals. Used for measuring illumination, recording light fluctuations, etc., similar to a photoresistor | |
 | A semiconductor device designed to switch an electrical circuit. When a small positive voltage is applied to the control electrode relative to the cathode, the thyristor opens and conducts current in one direction (like a diode). The thyristor closes only after the current flowing from the anode to the cathode disappears, or the polarity of this current changes. The terminals of the anode, cathode and control electrode are not indicated by letters in the diagram | |
| A composite thyristor capable of switching currents of both positive polarity (from anode to cathode) and negative (from cathode to anode). Like a thyristor, a triac closes only after the current flowing from the anode to the cathode disappears, or the polarity of this current changes | ||
 | A type of thyristor that opens (starts passing current) only when a certain voltage is reached between its anode and cathode, and closes (stops passing current) only when the current decreases to zero, or the polarity of the current changes. Used in pulse control circuits | |
| A bipolar transistor, which is controlled by a positive potential at the base relative to the emitter (the arrow at the emitter shows the conditional direction of the current). Moreover, when the base-emitter input voltage increases from zero to 0.5 volts, the transistor is in the closed state. After further increasing the voltage from 0.5 to 0.8 volts, the transistor operates as an amplification device. At the final section of the “linear characteristic” (about 0.8 volts), the transistor is saturated (fully open). A further increase in the voltage at the base of the transistor is dangerous; the transistor may fail (a sharp increase in the base current occurs). According to the textbooks, a bipolar transistor is controlled by a base-emitter current. Direction of switched current in npn transistor– from collector to emitter. The base, emitter and collector terminals are not indicated by letters in the diagram | ||
| A bipolar transistor, which is controlled by a negative potential at the base relative to the emitter (the arrow at the emitter shows the conditional direction of the current). According to the textbooks, a bipolar transistor is controlled by a base-emitter current. Direction of switched current in pnp transistor– from emitter to collector. The base, emitter and collector terminals are not indicated by letters in the diagram | ||
| A transistor (usually n-p-n), the resistance of the collector-emitter junction of which decreases when it is illuminated. The higher the illumination, the lower the junction resistance. Used for measuring illumination, recording light fluctuations (light pulses), etc., similar to a photoresistor | ||
 | A transistor whose drain-source junction resistance decreases when voltage is applied to its gate relative to the source. It has a high input resistance, which increases the sensitivity of the transistor to low input currents. Has electrodes: Gate, Source, Drain and Substrate (not always the case). The principle of operation can be compared to a water tap. The greater the voltage on the gate (the greater the angle the valve handle is turned), the greater the current (more water) flows between the source and drain. Compared to a bipolar transistor, it has a larger range of regulating voltage - from zero to tens of volts. The gate, source, drain and substrate terminals are not indicated by letters in the diagram | |
 | A field-effect transistor controlled by a positive gate potential relative to the source. Has an insulated shutter. It has a high input resistance and a very low output resistance, which allows small input currents to control large output currents. Most often, the substrate is technologically connected to the source | |
 | A field-effect transistor controlled by a negative potential at the gate relative to the source (for remembering, the p-channel is positive). Has an insulated shutter. It has a high input resistance and a very low output resistance, which allows small input currents to control large output currents. Most often, the substrate is technologically connected to the source | |
 | A field-effect transistor that has the same properties as “with a built-in n-channel” with the difference that it has an even higher input resistance. Most often, the substrate is technologically connected to the source. Using insulated gate technology, MOSFET transistors are made, controlled by an input voltage from 3 to 12 volts (depending on the type), having an open drain-source junction resistance from 0.1 to 0.001 Ohm (depending on the type) | |
 | A field-effect transistor that has the same properties as “with a built-in p-channel” with the difference that it has an even higher input resistance. Most often, the substrate is technologically connected to the source |
The name diode translates as “two-electrode”. Historically, electronics originates from electric vacuum devices. The fact is that the lamps, which many remember from old televisions and receivers, bore names such as diode, triode, pentode, etc.
The name included the number of electrodes or legs of the device. Semiconductor diodes were invented at the beginning of the last century. They were used to detect radio signals.
The main property of a diode is its conductivity characteristics, which depend on the polarity of the voltage applied to the terminals. The diode designation tells us the conducting direction. The movement of the current coincides with the arrow on the UGO diode.
UGO – conventional graphic designation. In other words, this is an icon that denotes an element on the diagram. Let's look at how to distinguish the LED designation on the diagram from other similar elements.
Diodes, what are they?
In addition to individual rectifier diodes, they are grouped according to application into one housing.
Designation of the diode bridge For example, this is how it is depicted diode bridge for rectification of single-phase AC voltage. And lower appearance diode bridges and assemblies.
Another type of rectifier is Schottky diode– designed for operation in high-frequency circuits. Available both in discrete form and in assemblies. They can often be found in pulse blocks power supply, for example power supply for personal computer AT or ATX.
Typically, on Schottky assemblies, its pinout and internal connection circuit are indicated on the case.
Specific diodes
We have already looked at the rectifier diode, let's take a look at Zener diode, which in Russian literature is called - zener diode.
Zener diode designation (Zener diode) Outwardly, it looks like a regular diode - a black cylinder with a mark on one side. Often found in a low-power version - a small red glass cylinder with a black mark on the cathode.
It has an important property - voltage stabilization, therefore it is switched on parallel to the load in the opposite direction, i.e. The plus of the power supply is connected to the cathode, and the anode to the minus.
The next device is varicap, the principle of its operation is based on changing the value of the barrier capacitance, depending on the magnitude of the applied voltage. Used in receivers and in circuits where it is necessary to perform operations on the signal frequency. Designated as a diode combined with a capacitor.
Varicap - designation on the diagram and appearance – the designation of which looks like a diode crossed across. In fact, this is what it is - it is a 3-junction, 4-layer semiconductor device. Due to its structure, it has the property of passing current when overcoming a certain voltage barrier.
For example, dinistors of 30V or so are often used in “energy-saving” lamps, to start an autogenerator, and other power supplies built according to such a circuit.
Dinistor designation LEDs and optoelectronics
Since the diode emits light, the designation means LED there should be an indication of this feature, so two outgoing arrows were added to the usual diode.
In reality there are many different ways determine the polarity, there is more information about this below, for example, the pinout of the green LED.
Typically, an LED's pins are marked either with a mark or with legs of different lengths. The short leg is a minus.
Photodiode, the device is the opposite in action to the LED. It changes its conductivity state depending on the amount of light falling on its surface. Its designation:
Such devices are used in televisions, tape recorders and other equipment that is controlled by remote control. remote control in the infrared spectrum. Such a device can be made by cutting off the body of a regular transistor.
Often used in light sensors, devices automatic switching on and turning off lighting circuits, for example:
Optoelectronics is a field that has become widespread in data transmission and communication and control devices. Thanks to its fast response and galvanic isolation capability, it ensures safety for the powered devices in the event of a high-voltage surge on the primary side. However, not in the form as indicated, but in the form of an optocoupler.
At the bottom of the diagram you see an optocoupler. The LED is turned on here by closing the power circuit using an optotransistor in the LED circuit. When you close the switch, current flows through the LED in the optocoupler, in the bottom square on the left. It lights up and the transistor, under the influence of the light flux, begins to pass current through LED1, marked green.
The same application is used in circuits feedback by current or voltage (to stabilize them) of many power supplies. The scope of application starts from chargers mobile phones and power supplies LED strips, to powerful power supply systems.
There are a great variety of diodes, some of them are similar in their characteristics, some have completely unusual properties and applications, they are united by the presence of only two functional terminals.
You can find these elements in any electrical circuit; their importance and characteristics cannot be underestimated. Correct selection diode in the snubber circuit, for example, can significantly affect the efficiency and heat dissipation of power switches, and, accordingly, the durability of the power supply.
If there was anything unclear to you, leave comments and ask questions; in the following articles we will definitely reveal all the unclear questions and interesting points!
Lecture No.4
Semiconductor diodes
The figure below shows a conventional graphic designation of a semiconductor diode on circuit diagrams.
Classification of semiconductor diodes
- Rectifier diodes;
- Schottky diodes;
- Pulse diodes;
- Microwave diodes;
- Varicaps;
- Voltage stabilizing diodes (zener diode, two-anode zener diode, stabilizer);
- LEDs;
- Photodiodes;
- Optocoupler (LED+photodiode);
- Tunnel diode.
Conventional graphic symbols of diodes of different types
Diode operating principle
The principle of operation of a semiconductor diode is based on a p-n junction. The anode corresponds to the p transition region, and the cathode corresponds to the n region. About physics work p-n transition can be read in the book by E.A. Moskatova “Electronic technology”. In this lecture, the phrases diode and pn junction will be used as synonyms. Every p-n junction can work as a diode, but not every diode is a p-n junction The fact is that there are Schottky diodes that use the properties of the Schottky junction (metal-semiconductor contact).
If the voltage at the anode is greater than the voltage at the cathode, the diode is on in the forward direction.
If the voltage at the anode is less than the voltage at the cathode, the diode is on in the opposite direction.
As the forward voltage across the diode increases, its resistance decreases and the current through the diode increases. In the absence of forward voltage, and even more so when reverse voltage (reverse bias) is applied to the diode, the resistance p-n junction so large that it can be considered a break in the circuit. With a forward voltage drop across the diode of 0.6-0.7 volts, the diode resistance ranges from several tens to several hundred Ohms.
The above is clearly confirmed by the current-voltage characteristic of a semiconductor diode:
The current through the pn junction is described by the formula:
where I 0 is the current caused by the passage of its own charge carriers;
e – base of natural logarithm;
e’ – electron charge;
T – temperature;
U – voltage applied to the p-n junction;
k – Boltzmann constant.
– temperature potential, at room temperature equal to approximately 0.025 V.
The properties of the p-n junction depend significantly on the ambient temperature. As the temperature increases, the generation of pairs of charge carriers—electrons and holes—increases, i.e. the concentration of minority carriers and the intrinsic conductivity of the semiconductor increases, which primarily affects the change in the reverse current. As the temperature increases, the reverse current increases approximately 2 times with a change in temperature () for every 100C for germanium diodes and for every 7.50C for silicon diodes.
The maximum permissible increase in reverse current determines the maximum permissible temperature of the diode, which is 80 ... 100 ° C for germanium diodes and 150 ... 200 ° C for silicon diodes.
The minimum permissible temperature of the diodes is within minus (60 ... 70) °C.
When a certain reverse voltage value is reached on the diode, the resistance of the diode decreases sharply and the current through the diode increases greatly. This phenomenon is called p-n breakdown transition. The breakdown of the pn junction (diode), in turn, can be reversible and irreversible. Reversible breakdown is used to stabilize voltage using zener diodes.
An important class of diodes are Schottky diodes. The voltage drop across a Schottky diode in the open state is 0.3 volts (as opposed to 0.6-0.7 volts for a pn junction diode). Conventional graphic designation of Schottky diodes in the diagrams:
Frequency properties of diodes, barrier capacitance
The frequency properties of a pn junction show how a pn junction works when a high frequency alternating voltage is applied to it. The frequency properties of a pn junction are determined by two types of junction capacitance: barrier and diffusion.
The first type of capacitance is the capacitance caused by the immobile charges of donor and acceptor impurity ions. It is called charging or barrier capacitance
Relative dielectric constant of the medium filling the space between the plates (in a vacuum it is equal to unity);
Electric constant, numerically equal to 8.854187817.10 − 12
S p - n – area p-n transition;
The second type of capacitance is diffusion capacitance, caused by the diffusion of mobile charge carriers through the p-n junction at direct connection.
Q is the total charge flowing through the p-n junction.
Equivalent p-n circuit transition.
Ri is very small with direct connection and will be large with reverse connection.
If an alternating voltage is applied to the p-n junction, then the capacitive reactance of the p-n junction will decrease with increasing frequency, and at some high frequencies the capacitive reactance may become equal to internal resistance p-n junction with direct connection. In this case, when turned back on, a sufficiently large reverse current will flow through this capacitance, and the p-n junction will lose its property of one-way conductivity.
Conclusion: the smaller the capacitance of the pn junction, the higher frequencies it can operate.
The frequency properties are mainly influenced by the barrier capacitance, since diffusion capacitance occurs during direct connection, when the internal resistance of the pn junction is low.
Rectifier diodes
The main task of the diode is to rectify alternating current/voltage using valve properties p-n transition.
If you remember that a diode is a conductor that allows current to flow in only one direction, then it is not difficult to understand how a rectifier circuit works. The presented scheme is called half wave rectifier, since it only uses half the input signal (half the period).
If the rectified current is greater than the maximum permissible forward current of the diode, then parallel connection of diodes is allowed
Additional resistances Rd ranging from units to tens of Ohms are included in order to equalize the currents in each of the branches.
If the voltage in the circuit exceeds the maximum permissible reverse voltage of the diode, then in this case the diodes can be connected in series
Shunt resistances of several hundred kOhms are included to equalize the voltage drop across each diode.
A half-wave rectifier is inefficient, since we lose half the voltage per period, so the output voltage is half as much.
To eliminate this drawback, a full-wave rectifier is used:
During the positive half-cycle of voltage Ua (+), diodes VD1 and VD4 are open, and VD2 and VD3 are closed. The current will flow along the path: upper branch (+), diode VD1, load, diode VD4, lower branch (-).
During the negative half-cycle of voltage Ua, diodes VD1 and VD4 close, and diodes VD2 and VD3 open. The current will flow from (+), lower branch, diode VD3, load, diode VD2, upper branch (-).
Therefore, the current through the load will flow in the same direction during both half-cycles. The rectifier circuit is called full-wave.
Signals rectified by a diode motor (full-wave circuit) cannot yet be used as DC signals. The point is that they can be considered signals direct current only in the sense that they do not change their polarity. In fact, they contain a large amount of "ripple" (periodic fluctuations in voltage around a constant value), which must be smoothed out in order to obtain a true DC voltage. To do this, the rectifier circuit must be supplemented with a low-pass filter.
Resistor R in the above circuit is used. Not necessary, since the diode bridge has a certain output resistance.
Supply voltage splitting. A widely used bridged single-phase full-wave rectifier circuit is shown in the figure below. It allows you to split the supply voltage (receive equal output voltages of positive and negative polarity). This circuit is efficient because each half-cycle of the input signal uses both halves of the secondary winding.
Electrical diagram- this is a text that describes the content and work with certain symbols electrical device or a set of devices that allows you to express this text in a concise form.
In order to read any text, you need to know the alphabet and reading rules. So, to read diagrams, you should know the symbols - conventions and rules for deciphering their combinations.
The basis of any electrical circuit is graphic symbols various elements and devices, as well as connections between them. The language of modern circuits emphasizes in symbols the main functions that the depicted element performs in the circuit. All correct conventional graphic designations of electrical circuit elements and their individual parts are given in the form of tables in the standards.
Conventional graphic symbols are formed from simple geometric shapes: squares, rectangles, circles, as well as from solid and dashed lines and dots. Their combination according to a special system, which is provided by the standard, makes it possible to easily depict everything that is required: various electrical devices, instruments, electrical machines, mechanical and electrical connection lines, types of winding connections, type of current, nature and methods of regulation, etc.
In addition, in the conventional graphic symbols on electrical circuit diagrams, special symbols are additionally used to explain the operating features of a particular circuit element.
For example, there are three types of contacts - normally open, normally closed and switching. Legend reflect only the main function of the contact - closing and opening the circuit. To specify additional functionality specific contact The standard provides for the use of special signs applied to the image of the moving part of the contact. Additional signs allow you to find contacts, time relays, limit switches, etc. on the diagram.
Individual elements on electrical diagrams have not one, but several designation options on the diagrams. For example, there are several equivalent options for designating switching contacts, as well as several standard designations for transformer windings. Each of the designations can be used in certain cases.
If the standard does not contain the required designation, then it is compiled based on the principle of operation of the element, designations adopted for similar types of devices, devices, machines in compliance with the design principles stipulated by the standard.
Standards. Conventional graphic symbols on electrical and automation diagrams:
GOST 2.710-81 Alphanumeric designations in electrical circuits: