The name "capacitor" was introduced in the late XVIII century, when there was an idea of the "electric fluid" and the capacitor was seen as a device for condensation, condensation of these liquids. Now it is an outdated name still persists in all languages except English, where instead of the old term condenser is already widely used term capacitor. In domestic technical literature common term is a combination of "capacitance" when talking about the size of the vessel.
The first information on the capacitors are middle of the XVIII century. These capacitors were the glass vessels filled with water, which served as the first sheath and join the electrostatic generator. The second plate of the hand served as the experimenter, is applied to the bottom of the glass vessel. Application capacitor dramatically enhance the effect of electrostatic discharge low-power generator, who was at that time the only source of electricity.
Priority in the invention of the condenser initially attributed Mushenbroku Wang, a professor at Leiden University (Netherlands). Hence the name "Leyden jar" to a glass condenser. However, more correctly regarded as the inventor of the condenser Ewald Georg von Kleist, the prelate of the cathedral in the town of Kamina (Germany) . Date of invention of the condenser - October 11, 1745 The first information about the appearance of capacitors in Russia belong to the 1752 Glass jars, filled with lead shot and pasted outside the metal foil used by MV Lomonosov and G. Richter in the study of atmospheric electricity.
Getting technical application of capacitors is to the middle of the XIX century. In 1856 he was granted English patent Ishamu Baggsu to use glass capacitor discharge for ignition of gas lamps, as well as for wiring, which can be regarded as the first use of a capacitor in communication technology. In 1877, PN Yablochkov was issued a French patent for a "distribution system and increase atmospheric electricity currents obtained from one light source to simultaneously supply multiple fixtures. This date may be considered the beginning of the application of capacitors in the power electrical engineering.
Until the end of XIX century the technical use of capacitors was limited. The need for their wide industrial production arose only after the invention of radio in 1895 by AS Popov. Due to the rapid development of production of radio stations, especially for the navy, already in the first years of XX century abroad raises a number of companies specializing in the manufacture of capacitors.
In electronics and electrical energy, capacitors are used in other non-electrical engineering fields and industries, particularly in metal - in the high-frequency apparatus for melting and heat treatment of metals in the spark (electric-spark) installations; for magneto-pulse treatment of metals, extractive industry (coal, metal ore, etc.) - to transport ore to the condenser electric locomotives normal and high frequency (contactless) in electroexplosive devices, in devices using the electrohydraulic effect, etc.
The diversity of applications makes exceptionally large variety of types of capacitors used in modern technology. Along with tiny capacitors that have weight less than a gram and the size of the order of several millimeters, can be found capacitors weighing several tons and a height exceeding the height of a man. The capacity of modern capacitors can be from a fraction of picofarads up to several farads, and the nominal operating voltage may lie in the range of a few volts to hundreds of kilovolts.
The electrical properties, structure and scope of the condenser to the maximum extent determined by the dielectric, separating its sheath. Because capacitors correct to classify by the nature of the dielectric.
Capacitors: a gaseous dielectric - air, gas-filled and vacuum, with a liquid dielectric, with the inorganic solid dielectric - glass (vitreous enamel, glass, stekloplenochnye), mica, ceramic (low frequency and high frequency), thin layer of inorganic films, with solid organic dielectric : paper, metallobumazhnye, film (from the non-polar films and films from polar), combined - bumazhnoplenochnye, thin layer of organic synthetic films (thin film), electrolytic (oxide): aluminum, tantalum, niobium, titanium, these capacitors can also be distinguished by the type for liquid, dry, solid (oxide-semiconductor) and oxide-metal.
Variable capacitor: mechanically controlled value of the capacitance, dielectric materials with gas: air, gas-filled, vacuum, liquid dielectric, with a solid dielectric: ceramic, glass, plastic, electrically controlled value of the capacitance - segnetokeramicheskie (variconds) and semiconductors (varicap).
For a given type dielectric capacitors can be classified as an additional mode, for which the capacitor is designed. At the same time distinguish the following basic modes: 1) at a constant or a rectified voltage, and 2) when an alternating voltage of 50 Hz technology, and 3) in the audio frequency 20 ... 20 000 Hz, and 4) at radio frequencies, 5) in pulsed mode ( with single pulses or repetitive pulses of constant or variable polarity).
U condensers for use in electronics in the marking usually indicates the nominal operating voltage direct current. For power capacitors usually indicates the effective value of operating voltage at a frequency of 50 Hz.
In everyday practice of capacitors using the following parameters.
Nominal capacity - capacity, the value of which is marked on the capacitor or indicated in the documentation. Nominal values tanks are standardized and are selected from certain series of numbers. For example, according to the standard CMEA '6 -78 has seven series: E3, E6, E12, E24, E48, E96, E192. Figures after you E indicate the number of nominal values in each decimal range (decade). For example, a number of E6 contains six values of the rated capacity in each of them obtained by multiplying or dividing by 10 °, where n - integer positive or negative number. In the manufacture of capacitors are most often used rows of E3, E6, E12 and E24, less often - E48, E96 and E182.
Actual capacity may vary from the nominal within the allowable tolerances. The latter indicates a percentage in accordance with a number:
± 0,1; ± 0,25; ± 0,5; ± 1; ± 2; ± 10; ± 20; ± 30; 0 +50, -10 +30, -10 +50, -10 +100 -- 20 +50, -20 +80.
For capacitors with a rated capacity of less than 10 pF permissible deviations specified in absolute values: ± 0,1; ± 0,25; ± 0,5 and ± 1 pF.
Rated voltage - the voltage value that is indicated on the capacitor or specified in the documentation, in which he can work in the specified conditions within a fixed period of service with the persistence of the parameters within acceptable limits.
Rated voltage of many types of capacitors decreases with increasing ambient temperature, as temperature increases, as a rule, accelerated aging process of the dielectric. When using capacitors for AC or DC current with the imposition of the variable component of the voltage necessary to fulfill the following conditions.
1. The amount of DC voltage and amplitude of the variable component should not exceed the allowable stress, which is stated in the documentation;
2. The amplitude of the AC voltage must not exceed the value of voltage, calculated on the basis of allowable reactive power:
U = 565000 * sqr (P / Fc), where U - the amplitude of the AC voltage, V, P - allowable reactive power, VARS (volt x ampere reactive); F - Frequency, Hz;
C - Capacitance, pF.
For capacitors with a rated voltage of 10 kV and less than the rated voltage set in accordance with GOST 9665-77 from the series:
1, 1,6, 2,5, 3,2, 4, 6,3, 10, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315; 350, 400, 450, 500, 630, 800, 1000, 1600; 2000; 2500; 3000, 4000, 5000, 6300, 8000; VA 10000
Under the nominal current of the capacitor to understand the most current at which the capacitor can be operated in the given conditions for the guaranteed service life. The value of the nominal current depends on the design of the condenser, applied to its contents, frequency of the alternating or pulsed voltage and ambient temperature. When passing through a capacitor value of radio pulse current I may exceed the rated current Ir
according to the relation: I = Ir * sqr (Q), where Q - duty cycle pulses.
The value of the nominal current in amperes vacuum capacitors installed in accordance with GOST 14611-78 from the series: 5, 7,5, 10, 12, 15, 20, 25, 30, 35, 40, 50: 60, 75, 100, 125, 150; 200, 250, 300, 400, 500, 600, 750, 1000.
Dissipation Factor tgb characterizes the energy loss in the capacitor and is determined by the ratio of active to reactive power at a sinusoidal voltage of a certain frequency: tgb = Pa / Pp.
The specific value of loss tangent depends on the type of dielectric and its quality, as well as the ambient temperature and the frequency of alternating current, at which it is measured. Typically, tgb has a minimum at room temperature. With increasing frequency value tgb increases. Over time, as well as during operation in wet environments tgb value increases and may increase several times.
The electrical resistance of the capacitor dc voltage is a certain resistance to the isolation condenser. This parameter is characteristic of capacitors with organic and inorganic dielectrics. For more capacitors 0,33 uF taken instead of insulation resistance value of the constant lead time, expressed in seconds, equal to the product of insulation resistance value of the rated capacity. Insulation resistance (time constant) depends on the type of dielectric, the capacitor structure and conditions of its operation. For prolonged storage insulation resistance may be reduced by one to three orders of magnitude.
Conduction current passing through the condenser at a constant voltage on its plate of the steady state, is called leakage. Leakage due to the presence in the dielectric of free charge carriers and characterizes the quality of the dielectric capacitor. This setting is typical for vacuum and oxide capacitors. Leakage current is highly dependent on the value of the applied voltage and the time within which it is applied. Leakage current is measured through 1 ... 5 min after the filing of a capacitor rated voltage. When the capacitor voltage is under the "training", ie gradual decrease in leakage current. With long-term storage and long-term work of the leakage current of capacitors increases.
Temperature coefficient of capacitance (TKE) - the size used for the characterization of capacitors with a linear dependence of capacitance on temperature and equal to the relative change in capacitance with change in ambient temperature by one degree Celsius. As the value of TKE and some other ceramic capacitors are divided into groups. For capacitors with a nonlinear dependence of capacitance on temperature, as well as with great deal of care capacity on temperature is usually given as the relative change in capacitance in the working temperature range.
Impedance capacitor - a capacitor opposition sinusoidal alternating current of a certain frequency due to the presence of a real capacitor, along with the capacity of the active resistance and inductance. This option is typically used when using a capacitor in the microwave devices. Have the smallest inductance ceramic capacitors (1 ... 30 nH).
Reactive power - is the product of a certain frequency voltage applied to the capacitor, the strength of current passing through it, and the sine of the angle of phase shift between them. In most cases, the angle of phase shift is close to 90 °, so approximately Pp == 2Pi / (CU2). The concept of reactive power given to high and especially high-voltage capacitors and used to establish allowable electric modes of operation. Thus in the low-frequency limits are permissible amplitude AC voltage, and at high frequencies - allowable reactive power the capacitor.
Insertion attenuation and resistance to communication - it is the values characterizing the ability of capacitors and EMI filters to suppress interference AC given frequency. Insertion attenuation (A) is proportional to the logarithm of the ratio of the voltage measured at the load circuit before (U1) and after (U2) inclusion of a capacitor or filter in this chain: A = 20lg (U1/U2).
Resistance connection Rc defined as the ratio of output voltage Uin EMI capacitor, its input current Ivh, ie Rc = Uin / Ivh. The notion of coupling resistance given for 3 - and 4-pin capacitor.
Insertion attenuation and coupling impedance depend on the frequency of alternating current, capacitance, inductance, quality factor and the construction of capacitors and filters, as well as the output resistance of the generator and the load resistance.
Trimmer and variable capacitors have additional parameters that take into account the peculiarities of their functional purpose and meaningful performance. Instead of setting the nominal capacity settings are used the maximum and minimum capacitance, which can be obtained by moving the mobile system. Specific parameters and trimming capacitors are variable torque, agility and endurance capacity.
By trimmer capacitor with electric controls are ferroelectric and semiconducting. To control the volume of ferroelectric capacitors (variconds) uses characteristic of the spontaneous polarization dependence of the dielectric constant on the applied voltage to the capacitor plates. To control the volume of semiconductor capacitor (varicap) used the dependence of capacitance p-n-junction of the voltage.
Since the spontaneous polarization of the dielectric constant can reach huge values of order 10000 and is even higher, then for variconds characterized by high values of capacitance in small sizes of capacitors. For semiconductors - silicon and germanium - it is substantially less, about 11 ... 15, therefore the upper limit of capacity at the semiconductor capacitors is much lower than variconds, and usually does not exceed tens of picofarads, rarely exceeds several hundred. However variconds have serious disadvantages (strong temperature dependence, temporal instability, low Q factor - about 25 at best). Nevertheless, the ferroelectric capacitors were used in the dielectric amplifiers, frequency multipliers, voltage regulators, etc.
Semiconductor capacitors, yielding a ferroelectric largest rated capacity, have improved the stability of capacitance (for a given value of voltage) in both time and temperature changes. Quality factor of these capacitors is also increased in certain frequency range can not exceed 1000, accounting for no less than 25 ... 50, with frequencies of the order of tens of megahertz. Although the largest Q-factor of stability and capacity of these capacitors inferior air, but they are much smaller in size and weight, as well as increased reliability, allowing their use in a variety of equipment for the automatic configuration and tuning frequency, phase, etc. In addition, the semiconductor capacitors can be used in many other cases where the required capacity, depending on strength, competing with segnetokeramicheskimi capacitors particularly well for small values of capacitance and in cases where its stability are increased requirements, as well as reduced losses when they needed .
To characterize KU uses the following parameters.
Sensitivity - the minimum value of the input parameter, which is an abrupt change in the output parameter (circuit or interruption of contacts with non-contact - to change the conductivity). Depending on the type of input variable, which react to KU, the sensitivity can be estimated as current, voltage, power, mechanical power, luminous flux, magnetic field, etc.
Response time - characterizes the performance of the device. It is measured from the date of the input signal until the signal at the output. Time, reckoned from the date of termination of the control signal until the appropriate signal (abrupt changes) at the output is the time of release.
Maximum switching capacity - the product of the maximum allowable values of voltage and current at a given voltage. If the executive system KU commutes a few circuits, then introduce the concept of total switching capacity.
Frequency of operation (switching) - the number of positives KU per unit time.
Gain (sometimes called the coefficient of control) is determined by the ratio of power output to power management.
Input Impedance - defines the possibility of harmonizing the device with a source of control signals, and most often appears in the form of active (eg measures to resist the winding electromagnetic relays) or complex resistance.
Electric properties of DF are characterized by resistance and electric strength of insulation between current-carrying chains, as well as housing.
Resistance switching elements depends on the principle of switching and type of used items. To contact CG - is active resistance of closed contacts, for semiconductor-internal resistance of the device in the open state, for magnetic - AC inductive reactance, etc.
When using electrical contact occurs very complex physical processes, which have differences in their opening and closing .
Loopback. When reducing the distance between the contacts up to 10 microns observed gazorazryada process, and voltage ignition of gas between the contacts is determined by the Paschen law. At smaller distances, this law is violated. The boundaries correspond to several mean free path of molecules in the air at normal pressure. Therefore the electrons can cross the contact gap without collisions with gas molecules.
The electric field for the closure of contacts increases according to the law E = U / d, where E - electric field; U - switching voltage; d - the distance between the contacts. When the field strength of about 3 108 V / m there is the field emission of electrons from the surface of the cathode contact, which forms a short arc. This arc is besplazmennoy and is characterized by independence arcing voltage on the magnitude of current. In the presence of short films on the contact arc occurs at lower electric field.
Short arc heats the anode contact, and causes the transfer of material on the cathode contact. Immediately before the liquid is formed by contact contact contact isthmus and the tension within -10 ns abruptly drops to before lei volts. With further rapprochement between contact area of contact between WHO melts, transitional contact resistance decreases and, consequently, decreases as the temperature. Contact Isthmus freezes, but is easily broken under normal loads in the process of breaking contacts.
Breaking mode. In the process of breaking the contact pressure decreases, the contact surface micro-roughness becomes smaller, the current density and the transient resistance increase. Within a relatively short time, the voltage at the contacts increased from a few millivolts up to 0,5 ... 15 V. During this part of the process of breaking the contact points between the metal contacts are melted, and then they break when you reach the boiling point of the metal contacts. At this point, the voltage at the contacts abruptly (within approximately 10 ns) rise to arcing voltage short arc, and the time of its burning is much greater than for the closure. In this mode breaking contacts are destroyed more than closure.
When using electrical contacts to the power load characteristic for the electrical equipment, a short arc can move to a normal, plasma arc. In this case, changes the direction of transport of the material of contacts (from the cathode to the anode), and at break of liquid contact with the isthmus and the short arc transfer occurs from the anode to the cathode.
Depending on the purpose resistors resistors are divided into general and special (and ultra-precision, high-frequency, high voltage, high-mega-ohm).
Resistors general used as different loads, sinks and dividers in the supply circuits, filter elements, shunts, in chains, pulses, etc. The range of nominal resistance of 1 ohm resistors ... 10 MW, the nominal capacity of the scattering 0,062 ... 100 watts. Permissible deviation of resistance from the nominal value ± 1; +2; ± 5; ± 10; ± 20%.
Precision resistors and ultra-distinguished by high stability of parameters in the operation and manufacture of high precision (tolerance of i ± 0,0005 to 0,5%). They are used mainly in measuring devices, in various computing devices, computers and automation systems.
High-frequency resistors (resistors with a "depressed" reactivity), characterized by its own low inductance and capacitance, are used in high frequency circuits, cables and waveguides electronic equipment as matching loads, attenuators, directional couplers, dummy antenna, etc. Neprovolochnye high resistors are capable of operating at frequencies up to hundreds of megahertz or more, and high wire - up to hundreds of kilohertz.
High voltage resistors are designed for high operating voltages (from several to tens of kilovolts). They are used as voltage dividers, spark arrester, sinks, in charging and discharge high voltage circuits, etc.
Vysokomegomnye resistors have a nominal resistance range from tens of megohms to several tera and are calculated on small operating voltages (100 ... 400 V). So they work in the unloaded mode and the power of the scattering of small (less than 0.5 W). High-megomnye resistors used in electrical circuits with small currents in night vision applications, dosimeters and instrumentation.
Depending on the method of mounting hardware both permanent and variable resistors can be performed for the printing and hinged mounting, as well as for micromodules and chip or to interface with them. Findings of a hinged mounting resistors may be hard or soft, axial or radial wire circular section or tape in the form of petals, etc. We resistors used in the chips and micromodules, as well as a microwave resistors in the findings may be used as part of their surface.
Depending on the method of protection against environmental factors resistors structurally performed: isolated, non-insulated, sealed and vacuum.
Bare resistors (coated or uncoated) did not allow touching her body chassis equipment. In contrast, isolated resistors have fairly good insulating coating (paints, compounds, plastics, etc.) and allow the body chassis or touch live parts of equipment.
Sealed potentiometers are sealed hull design, which eliminates the possibility of environmental influences on its inner space.
In vacuum resistors resistive element with the base is placed in a glass vacuum flask.
By the nature of resistance change all resistors are divided into fixed and variable. The latter, in turn, are divided into trimmers and tuning. At constant resistor resistance is fixed in the process of exploitation is not regulated. Variable adjustment potentiometers allow change of resistance in their operation in hardware. Resistance Trimmer change with an ad hoc or periodic adjustment and does not change in the operation of the equipment.
Depending on the material of the resistive element resistors are divided into the following groups: wire resistive element of the drawing or solid wire with high resistivity; neprovolochnye; metal foil with resistive element made of a foil of a certain configuration, deposited on an isolated basis.
Neprovolochnye resistors are divided into thin film (thickness - a nanometer) thick film (thickness - of a millimeter), volume (thickness - the unit millimeters). Thin film resistors are divided into metal-, metallookisnye and metallic resistive element in the form of mikrokompozitsionnogo layer of dielectric and metal or a thin oxide layer of metal or metal alloy, carbon and boro-uglerodistge conducting element which is a film of pyrolytic carbon or bororganicheskih compounds.
For thick-film resistors include lakosazhevye, cermet and resistors on the basis of conductive plastics. Volumetric resistors can be organic and inorganic binder insulator. The conductive resistive layers of thick-film and bulk resistors constitute a heterogeneous system (composition) of several phases obtained by mechanical mixing of conductive component, such as graphite or carbon black, metal or metal oxide, with organic or inorganic binders (resins, glass, enamel), a filler, a plasticizer and hardener. After appropriate heat treatment formed heterogeneous solid layer with the necessary set of resistive parameters.
Lako-soot tracks formed on the basis of synthetic resins in the form of lacquer solutions. Conductive component is carbon black. Resistors on these tracks is called lacquer and soot, lakoplenochnymi or film composite.
In single resistor industry also produced sets of resistors. A set of resistors is set resistors, placed, usually in the BGA packages or housings, coupled with chips. They are classified according to destination, type of resistive element and electronic circuit construction. Easiest set - a set of constant resistors, connected or not connected to the electrical circuit that has no functional dependence of the output signal from the input. Operational set - a set of constant resistor connected in electrical circuit having the functional dependence of the output signal from the input. Combination set - a set consisting of fixed and variable resistors.
The main characteristics of resistors include the following.
Nominal power - the greatest power that the resistor can dissipate in the given conditions for a guaranteed service life (operating time) while maintaining the parameters within established limits. Specific values of the nominal capacity of the scattering in watts installed GOST-s and are selected from the series: 0,01, 0,025, 0,05, 0,062, 0,125;
0,25, 0,5, 1, 2, 3, 4, 5, 8, 10, 16, 25, 40, 63, 80, 100, 160, 250, 500. Power P, which dispels the resistor in a particular circuit, determined by passing through it current I and voltage drop U, or through the nominal resistance, as P = RI * I or P = U * U / R.
Operating voltage at which the resistor can work, must not exceed the value calculated on the basis of nominal power and nominal resistance. It is limited mainly by thermal processes in the conductive element and the electrical resistance of the resistor and is selected from the series:
25, 50, 100, 150, 200, 250, 500, 750, 1000, 1500, 2500, 3000, 4000, 5000, 10 000, 20 000, 25 000, 35 000, 40 000, 60 000 V.
For variable resistor, this series is somewhat limited:
5, 10, 25, 50, 100, 150, 200, 250, 350, 500, 750, 1000, 1500, 3000, 8000 W.
Nominal impedance - electrical resistance, whose value is indicated on the resistor or specified in regulatory documents. The range of nominal resistance is set resistors for: permanent - from fractions of Ohm to several tera-ohms, variable wire - from 0.47 ohms to 1 Mohm; variables neprovolochnyh - from 1 ohm to 10 Mohm. The nominal resistance of resistors manufactured by domestic industry in accordance with the recommendations of the IEC (International Electrotechnical Commission), are standardized. For regular domestic production is set resistors six series: E6, E12, E24, E48, E96, E192, and for a variable resistor - a number of E6. The number following the letter E indicates the number of nominal values in each decimal range. For example, a number of E6 nominal resistance in each decade must comply with numbers 1, 1,5, 2,2, 3,3, 4,7, 6,8 or the number obtained by multiplying or dividing these numbers by 10n, where n - integer positive or negative number. The principle of constructing series E48, E98 and E192 is similar to the above, only increases the number of intermediate values.
Temperature coefficient (TCR) is a quantity that characterizes the relative change in resistance per degree Kelvin or Celsius. TCS is characterized by reversible change of resistance of the resistive element due to changes in temperature or changes in the electrical load. The smaller the TAS, the better temperature stability has a resistor. In practice, using the average value of temperature coefficient of resistance, which is defined in the range of operating temperatures using a special meter TCS. Values of TCS precision resistors range from a few to 100-106 1 / ° C, and resistors in the common-'values - from tens to +2000-1061 / ° C.
Proper noise resistors consist of thermal and current noise. The emergence of the thermal noise due to the fluctuation changes in the volume concentration of free electrons in the resistive element, resulting from their thermal motion. The frequency spectrum of thermal noise is continuous.
Current noise caused by fluctuations of the contact resistances between conductive particles, as well as cracks and irregularities of the resistive element. These fluctuations are due to changes in the area of contact between the individual conductive parts of the structure of the resistive element, the redistribution of stress in certain gaps between these particles, the emergence of new conducting chains in relatively large gaps under the influence of high electric field, etc.
Proper noise resistors is higher, the higher the temperature and voltage. Value of EMF noise for neprovolochnyh resistors - from fractions of units to tens and hundreds of microvolts per volt.
Some types of resistors, especially high-voltage and high-resistance, depending on the applied voltage can vary the resistance, thereby breaking the linearity of current-voltage characteristics. The reason is depending on the carrier concentration and mobility on the electric field. To assess the degree of nonlinearity of the voltage ratio is used. He determined the relative change in resistance of resistors, measured at test voltages, corresponding to 10 and 100% of its rated power scattering. The value of the coefficient voltage ranges for different types of resistors from a few to tens of percent.
Inductive elements are divided into inductors and transformers.
Upon designation by the inductors can be divided into four groups:
a) coil circuits
b) the coil connection
c) high-frequency inductors and
d) low-frequency inductors.
On the basis of constructive coil can be divided into single and multi-layered, cylindrical, spiral, toroidal, shielded and unshielded; coils without cores and coils with cores and others
Inductors are characterized by the following basic parameters: inductance and precision, good quality, in-house capacity and stability.
Single-layer coils are used at frequencies above 1500 kHz. Rewinding can be solid and with a forced step. Single-layer coils with positive steps are characterized by high quality factor (Q = 150 ... 400), and stability;
used mainly in short circuits (KB) and ultrashort (VHF) waves . Highly stable coil used in the circuits on the heterodyne KB and VHF, are wound with a slight tension wire, heated to 80 ... 120 S.
For coils with inductance above 15 ... 20 uH used solid single-layer winding. Feasibility of transition to a continuous winding is determined by the diameter of the coil. Approximate values of inductance, which is appropriate for the transition to a continuous winding:
Cage diameter (mm) 6 10 15 20 25
Inductance (uH a) 1.8 4 10 20 30
Coils with a continuous winding is also distinguished by high quality factor and is widely used in the circuits on short, intermediate and secondary waves, whether it is required inductance is not above 200 ... 500 uH. It is advisable to switch to multi rk winding is determined by the diameter of the coil. Approximate values of inductance, which is appropriate for the transition to a multi-layer winding:
Cage diameter (mm) 10 15 20 25 30
Inductance (uH in) 30 50 100 200 500
Inductance of single-layer coil is calculated by the formula:
L = 0,01 DN2 / (l / D +0.44), where L - the inductance (in uH), D - diameter of the coil (in cm), 1 - length of winding (in cm), N - number of turns.
Quality factor of one-layer coils is determined mainly by the diameter of wire and winding step (the distance between the turns) x. Found that at high frequencies, the optimal value of the diameter of the winding wire is determined from the expression: d = 0,707 x.
Multilayer coils are divided into simple and complex. Examples of simple namotok is a common multi-layer winding and winding "heap" (or in bulk). Not partitioned multilayer coils with simple winding differ lowered the quality and stability, high capacitance, require the use of frameworks. Inductance of a multilayer coil is calculated by the formula: L = 0,08 (DN) 2 / (3D +9 l +10 t), where L - the inductance of the coil, uH; D - average diameter of winding, cm; l-length of winding, cm; t -- thickness of the coil, cm; N - number of turns.
If given inductance and need to calculate the number of turns, then you should set the value D, l and t and calculate the required number of turns. This is followed to check the thickness of the coil according to the formula: t = zNd2 / l, where d - diameter of the wire with insulation (in mm), z = 1,05 ... 1,3 - factor is not winding density at d = 1 .. .0,08, respectively.
Partitioned inductors are characterized by a sufficiently high Q, low capacitance, a smaller external diameter and allow a small range of inductance adjustment by moving sections. They are used both as a contour in the contours of long and medium waves, and as a high-frequency ballasts. Each section is a standard multi-layer coil with a small number of turns. The number of sections may be from two to eight, sometimes even more. The calculation of partitioned coils is reduced to the calculation of inductance of one section. Inductance partitioned coil, consisting of n sections: L = Lc [n +2 k (n-1)], where Lc - inductance of the section, k - coupling coefficient between adjacent sections (k = 0.3 when the distance between sections, equal to half the width of the section, which is equal to the average radius of the coil).
Own capacity coil lowers the Q factor and the stability of adjustment circuits. In the areas of circuits, this capacitance reduces the coefficient of overlapping range. The value of capacitance is determined by the type and size of winding the coil. Smallest native capacity (a few pF) for single-layer coil wound with a forced step. Multilayer coils have a greater capacity, the magnitude of which depends on the method of winding. Thus, the capacity of coils with the universal winding is 5 ... 25 pF, and with ordinary multi-layer winding can be higher than 50 pF.
Called high frequency choke inductors used in power circuits as filter elements. Inductance throttle should be large enough, and their own capacity - small. Structurally high frequency inductors are performed in a single layer or multilayer coils. To choke the long and medium waves used partitioned multi-layer winding. Chokes for short waves and meter waves usually have a single-layer winding - solid or with a forced step. As the frame is often used ceramic rods of resistors. The calculation of the number of turns the throttle is the same as the calculation of the number of turns inductors.
In coils with a high inductance used cores of ferromagnetic materials. Inductance coil with a closed iron core L = 0,0126 mSN2/lc, [uH], where m - the permeability of the material (for electrical steels is in the range 200 ... 500), S - cross-section of the core (in cm2), N - number turns of the coil, 1 "- the average length of magnetic path, cm (for example, for a circular core - the length of its middle circle).
In technical terms and reference sheets for semiconductor diodes among the electrical parameters of isolated so-called classification parameters. These parameters from a group of semiconductor diodes choose the desired type (subtype). If the rectifier diodes as a classification parameter usually indicates the reverse voltage, the pulse diodes are classified according to the reverse recovery time of resistance, zener - voltage stabilizer, etc. Depending on the design, manufacturing technology and the appointment of diodes in technical terms and reference sheets may be given some classification parameters.
Rectifier diodes are designed for use in a variety of rectifier circuits, typically operating at currents of low frequency (50 ... 2000 Hz). For these diodes indicates the average value of direct current or rectified current (in the latter part of the reverse diode current during the action of the half-wave reverse voltage). The voltage drop across the diode at the same time characterized by the mean value of forward voltage for the period. If the rectifier is working on a capacitive load, the instantaneous value of direct current can greatly exceed the average value of current. The maximum electric mode using diodes characterized by the following parameters: peak reverse voltage - the voltage of any shape and frequency, the maximum direct current or rectified current, depending on the circuit of the diode.
High frequency diodes - devices universal purpose. They can be used for the rectification of the currents in a wide frequency range (up to several hundred MHz), modulation, detection, and other non-linear transformation of electrical signals. Properties of high-frequency diodes characterized by the following parameters: the voltage drop across the diode during the flow through it, a constant forward current, reverse current at a given reverse voltage, the differential resistance of the diode, operating frequency range, at any frequency range of the rectified diode current should not be less than the specified level compared with the value of the rectified current at a frequency of the lower limit of the range.
Pulsed diodes are designed for use as a key element in the scheme for small pulse durations and transient (microseconds and the proportion of microseconds). When short pulses is taken into account the inertia of the processes on and off the diodes. After the inclusion of direct current voltage on the diode is not established immediately. The time interval from the beginning of a pulse of direct current to the moment when the voltage across the diode falls to a specified level, called the time of establishment of direct resistance of the diode. The ratio of the maximum pulsed direct voltage across the diode to pulse direct current is pulsed diode resistance. When the flow of direct current in the diode base stored charge. When applying the reverse voltage, this charge is absorbed and causes the flow of pulse reverse current, which can be many times higher than the steady value of the reverse current. The time interval from the time when the current through the diode is zero, until the reverse current drops to a specified level, called the recovery time of the reverse resistance of the diode. Pulsed diodes are characterized by a small value of the barrier capacitance, measured as the capacitance between the findings at a given bias voltage.
Zener - Diodes, designed to stabilize voltage in the circuit when changing the current flowing through the diode. The main parameter stabilitron - voltage stabilization in the operating point for which is given by the differential resistance stabilitron - the ratio of voltage to stabilize called it a small change in the current stabilization. Normalized to the differential resistance with minimal current stabilization. An important parameter is the TKN (temperature coefficient of voltage stabilization) - the ratio of relative change in voltage to the absolute change in ambient temperature. TKN value is expressed as a percentage of 1 ° C. The stability of the diodes is characterized by the drift voltage stabilization, indicating the maximum absolute value of the voltage stabilization during a specified time. Normalized as stabilizing voltage variation from device to device. Diode, which is used to stabilize the direct branch of the CVC, called stabistorom. Voltage stabilization stabistorov is only a few tenths of a volt. Maximum mode for diodes and stabistorov characterized by a maximum current stabilization and maximum power dissipation.
The tunnel diode is characterized by its I-V plot with a negative differential resistance. Negative resistance remains to hundreds and thousands of MHz. The presence of the characteristics of the diode area with negative resistance makes it suitable for amplifiers, sinusoidal oscillators and relaxation oscillations, switching schemes.
Diodes Schottky diodes is different from the p-n-junctions lack of injection is not the major carriers. Oto means that they lack the diffusion capacitance associated with the accumulation and dispersal is not the main carriers in the base and Oto significantly increases the speed diodes changes the currents and voltages, including when switching from forward to reverse direction and return to direct. Time of switching is determined only by the barrier capacitance and a diode with a small area can be tenths and hundredths of a nanosecond. Corresponding operating frequencies are in the range 3 ... 15 GHz. No less important feature of the Schottky diode is much lower forward voltage compared with the voltage. p-n-junction. This is because CVC at the Schottky diodes is described by the same classical formula (4.7), that of the p-n-clicks, but the heat current is substantially larger because the diffusion rate, characteristic of p-n-junction, a Schottky diode is replaced by mean thermal velocity of carriers. Last exceeds the diffusion by about 3 order. In the same respect differences and thermal currents. Ultimately, this means that the direct voltage at the Schottky diodes will be about 0.2 in less than the p-n-junction. This distinction is sometimes very substantially, for example, when using such diodes to prevent saturation of transistor keys. Typical Schottky diodes are the direct voltage 0,4 V. With regard to the reverse currents, they can be, depending on the area, units and tenths of pikoamper, ie close to the actual counter-currents of silicon p-n-transitions determined thermal generation. Another feature of the Schottky diodes is that their direct IVC strictly obeys the exponential law (4.7) in a very wide range of currents - for several decades, from 1012 to 104 A. This implies the possibility of using Schottky diodes as a precision logarifmiruyuschih elements.
The fact that Schottky barriers have spread relatively recently (in the early 70's), although their theory was developed in the twenties was due, firstly, that in order to obtain high-quality barriers needed to implement the "organic" (non-clamping ) contact metal and a semiconductor, which was possible only after development of technology vacuum deposition of films. Secondly (especially for diodes), it was necessary to ensure low resistance base with a sufficiently high breakdown voltage, and this was achieved only after the development of epitaxial technology.
Transistors are divided into types (subtypes) of the classification parameters. For example, low-power low-frequency and medium frequency transistors are classified according to parameters such as current gain and cutoff frequency amplification or generation. In some cases, highlights the noises mainly the first stages, working on small signals. At the high frequency current amplification factors are complex numbers (as well as other H-parameters). Amplifying properties of transistors on a high frequency module, characterized by the gain of the current (alpha) |, | H21b | or | B]. The frequency at which the value | H21b | decreases by 3 dB (30%) compared with | H21b | measured at low frequency, called the marginal rate of the current amplification f ".
Module current amplification in the scheme of MA decreases with increasing frequency more markedly than in the scheme of OB. In a certain frequency range parameter | H21b | is inversely proportional to frequency: | H21e | = FT / F. Frequency FT - cutoff frequency increasing base current. At this frequency module | H21e | = 1. There is an approximate ratio: fa = mFt, where m = 2 for bezdreyfovyh m = 1,6 for drift transistors.
For small-signal parameters are also tank hits transistor. The capacity of the collector junction C - capacity, measured between the collector and the base pin of the transistor with the emitter off and reverse bias on the collector. Capacity of the emitter junction C - capacity, measured between the pin emitter and base-operating with the collector and the reverse bias on the emitter. Values tanks Sk and C, depend on the applied voltage. If, for example, set to Sp at a voltage U, then the capacity Skx at voltage U, can be found from the approximate formula: Skx = Ck (U / Ux) m, where m is determined in the same manner as in (4.5).
Maximum oscillation frequency F max - the maximum running frequency of oscillator transistor. With sufficient accuracy can be assumed that Fmaks - the frequency at which the gain of the transistor power is unity. It is connected with other small signal parameters of the approximate relation:
Noise Kw - the ratio of the total power of noise at the output transistor to a part of the power caused by the thermal noise resistance of the signal source. Noise is expressed in decibels. Its value is given for a specific frequency range. For most transistors, the minimum noise observed when working at frequencies of 1000 ... 4000 Hz. At the high and low frequency noise increases. Typically, the minimum value of Pn corresponds to the low collector currents (0,1 ... 0,5 mA) and low collector voltage (0,5 ... 1,5 V). Noise increases sharply with increasing temperature. Quoted in the reference data values of Pn are the optimal source impedance signal and mode, and that should be used when designing low-noise amplifiers.
The parameters characterize the large-signal operation modes in which the currents and voltages between the findings of the transistor vary within wide limits. These parameters are used to calculate the key schemes, pre-terminal and terminal amplifiers low and high frequency oscillators. Static current gain: Insert = (Ik-Iko) / (Ib + Iko). In this case, the collector current Ik and the current base Ib greatly exceed the thermal collector current Iko, therefore, in practice, use the formula: Insert = Ik / Ib
Static steepness of direct transmission Sst - the ratio of continuous collector current to a constant voltage at the input of the transistor. Parameter Sst transistors used for medium and heavy-duty, working in the schemes where the input source has a small internal resistance.
Tensions between the collector and emitter of the transistor in the saturation regime Ukn measured at a specific value of the collector and base currents, or a certain depth of saturation. The depth of saturation - the ratio of base current to direct current, where the transistor is at the edge of saturation. Tensions between the base and emitter of the transistor in the saturation regime Uben measured under the same conditions as the voltage Ukn.
Time resorption Tr - the time interval between the time of filing the base of the transistor reverse pulse and the moment when the collector voltage reaches the level (0,1 ... 0,3) Ek (Ek - voltage collector circuit). Time of dispersal depends on the depth of saturation of the transistor and is measured at a specific value of the collector and base currents.
Parameters limiting modes. Maximum power dissipated by the device - Pmax. Since the bulk of transistor power dissipation is allocated in the area of the collector junction, then this power is practically equal Kmaks - maximum power dissipated in the collector junction.
Maximum collector current Iк max - specifies the maximum collector current at maximum voltage on the collector and the maximum allowable power dissipation.
The maximum reverse voltage between the collector and base of the transistor Ukb max - This option is usually used to calculate the mode latch transistor or switch it to ON and the generator circuit current in the emitter circuit.
The maximum reverse voltage on the emitter-base junction Ueb max. This parameter is used to calculate the mode of operation when the input is valid reverse voltage (amplifier mode B, with different types of schemes).
Maximum voltage between the collector and emitter of the transistor Uke max subject to short-circuit the emitter to base. In some cases, this option is subject to the inclusion between the base and emitter resistor of a given resistance.
Uke max parameter is used in the calculation mode of the transistor included in the circuit with common emitter and in the absence of reverse voltage, or when it is small, for example, less than 1 V.
The maximum values of currents, voltages and power define the boundaries of guaranteed reliability. Since the work to the limit corresponds to the low reliability, the use of limiting regimes in the schemes, which are required high reliability, are not allowed.
Practice shows that the use of semiconductor devices in the ease of the reliability of their work increased tenfold compared with the reliability to the limit.
Thermal parameters of semiconductor devices set allowable limits or ranges of ambient temperature and the devices themselves, in which they are guaranteed reliable operation.
First Source: radiola.narod.ru Ed. 06.06 VF Gainutdinov