Lecture
INTRODUCTION
Electronics is a branch of science and technology that studies: physical phenomena in semiconductor devices; the electrical characteristics and parameters of semiconductor devices; and the properties of devices and systems based on the use of semiconductor devices.
Electrical conductivity of semiconductors
Simple semiconductor materials are used to manufacture semiconductor devices: elemental semiconductors such as germanium (Ge), silicon (Si), and selenium (Se), and compound semiconductor materials such as gallium arsenide (GaAs), gallium phosphide (GaP), and others.
In pure semiconductors the concentration of charge carriers - free electrons and holes - is low. Therefore, to give a semiconductor a specific type of conductivity, certain impurities are introduced into it. This process is called doping.
p-type semiconductor
The main charge carriers are holes.
Group III elements (Al, Ga) create hole conductivity.
n-type semiconductor
The main charge carrier is the electron.
Group V elements (vanadium V, niobium Nb) create electron conductivity.
An electron-hole junction, or p-n junction, is the region at the boundary between two semiconductors, one of which has electron conductivity and the other hole conductivity.
The component base of modern electronic devices
Classification of semiconductor devices
Semiconductor devices are devices whose operation is based on the use of the properties of the p-n junction
1. Resistors
2. Diodes
3. Transistors (BJT, FET, IGBT)
4. Thyristors
5. Integrated circuits
Semiconductor resistors
A semiconductor resistor is a semiconductor device with two leads that makes use of the dependence of the semiconductor's electrical resistance on voltage, temperature, illumination, and other controlling parameters.
Linear
A semiconductor resistor that uses a lightly doped material such as silicon or gallium arsenide. The resistivity depends only weakly on the electric field strength => resistance = const over a wide range of U and I. Used in integrated circuits.
Nonlinear
Varistor - a semiconductor resistor whose resistance depends on the applied voltage and whose current-voltage characteristic (I-V curve) is nonlinear.
Thermistor (temperature-dependent resistor) - a semiconductor resistor that makes use of the dependence of the semiconductor's electrical resistance on temperature.
• NTC thermistor: R↓ as t°↑
• PTC thermistor: R↑ as t°↑
Photoresistor - a semiconductor resistor whose resistance depends on illumination.
Strain gauge resistor - a semiconductor resistor whose resistance depends on mechanical deformation.
Diodes
Semiconductor diodes are semiconductor devices with a single p-n junction and two leads.
Classification of semiconductor diodes and their symbols
Designation system
1 - source material:
germanium - letter G or digit 1;
silicon - letter K or digit 2;
gallium - letter A or digit 3;
indium - letter I or digit 4
2 - device type:
A - microwave diodes
V - varicaps
D - rectifier and pulse diodes
I - tunnel diodes
L - emitting diodes (LEDs)
N - diode thyristors (dinistors)
S - zener diodes
Ts - rectifier stacks and assemblies
3 - digits denote certain key parameters of the diode (power) (for zener diodes, the fourth element characterizes the stabilization voltage),
4 - letters and/or digits denoting the design's serial number
5 - a letter defining the classification by parameters.
Planar rectifier diodes
Zener diode
Tunnel diodes
Varicaps
LEDs
Photodiodes
Point-contact diodes
Low-power
Rectifier
Microwave diodes
Current-voltage characteristic (I-V curve) of a real diode
For technical purposes the I-V characteristic is used in linear coordinates.
At high reverse bias voltages, breakdown may develop in the diode - a sharp increase in reverse current for a small change in voltage. In avalanche breakdown, electrons in the electric field of the p-n junction acquire enough energy to ionize the semiconductor's own atoms. This leads to avalanche multiplication of charge carriers, a sharp increase in their local concentration, and correspondingly in current. After avalanche breakdown develops, the diode does not lose its functionality. This type of breakdown is used in semiconductor zener diodes, whose properties will be discussed further below.
Thermal breakdown develops as a result of local heating of the p-n junction region and, as a consequence, an increase in charge-carrier concentration. Thermal breakdown is irreversible; after it, the diode loses its properties and functionality.
Current-voltage characteristic of an ideal diode
Main diode parameters
The parameter system is given in reference handbooks. This system makes it possible to correctly select a diode for use under specific conditions.
Ifwd - forward current flowing in the forward direction,
Ufwd - forward voltage,
Ifwd max - maximum available forward current,
Urev max - maximum available reverse voltage,
Irev - reverse current of the diode,
Urev - reverse voltage of the diode (constant voltage applied to the diode in the reverse direction).
Example: KD204A Ifwd = 2 A, Urev max = 400 V,
Ufwd = 1.4 V, Irev = 150 µA
As nonlinear elements, diodes are characterized by
static resistance Rs = U/I
differential (dynamic) resistance Rdiff = ∆U/∆I
Zener diodes
A zener diode is a semiconductor diode in which, in the breakdown region under reverse bias, the voltage depends only weakly on the current over a given range, and which is intended for stabilizing the voltage level in a circuit.
Actual I-V characteristic of a zener diode
Ideal I-V characteristic of a zener diode
Main parameters
1. Ust (stabilization voltage)
2. Differential resistance Rdiff = 0.5-200 Ohm
3. Ist min - minimum stabilization current
4. Ist max - maximum stabilization current
Imax ≈ Pmax/Ust
Silicon diodes, which have high resistance to thermal breakdown, are used as zener diodes.
Silicon zener diodes are used for stabilizing power supply voltages, as well as for clamping voltage levels in various circuits
Groups of low-power diodes in the form of diode matrices and diode assemblies are used in logic devices, decoders, and other computing-technology components.
A zener diode is usually connected into a stabilization circuit so that the p-n junction is reverse-biased.
For stabilizing small voltages of U = 1-1.5 V, voltage-reference diodes (stabistors) are used
Structural elements of integrated circuits
Package - the part of an IC's construction intended to protect the IC from external influences and to connect it to external electrical circuits by means of leads.
Substrate - a dielectric blank intended for depositing elements, interconnections, and contact pads onto it.
Board - part of the substrate, or the entire substrate, on the surface of which the film elements of the IC, its interconnections, and contact pads are deposited.
Semiconductor wafer - a blank of semiconductor material intended for manufacturing ICs;
Die (chip) - the part of the wafer in the volume and on the surface of which the elements of the semiconductor IC, its interconnections, and contact pads are formed;
Contact pad - a metallized area on the board, die, or IC package used for attaching the leads of components and dies, jumpers, and also for monitoring its electrical parameters and operating modes;
Chip-scale (unpackaged) IC - an IC die intended for mounting into a hybrid IC or micromodule;
Lead - a conductor electrically connected to the contact pad of the die and mechanically to its surface, to provide electrical contact with external circuits.
Main IC parameters
Packing density - the quantity per unit volume
Level of integration - the number of elements comprising the IC per 1 cm3
1st level of integration - up to 10 elements/cm3
2nd level of integration - 10-100 elements/cm3
3rd level of integration - 100-1000 elements/cm3
4th level of integration - up to 100,000 elements/cm3
and so on.
Classification of ICs by manufacturing technology
Semiconductor ICs - all elements of the IC are produced in a single technological cycle; all elements are formed in the volume and on the surface of a semiconductor die. Semiconductor ICs consume 50-200 mW.
Hybrid ICs - an IC that, in addition to elements, contains simple and complex components (several semiconductor ICs). Passive elements are formed by depositing various films onto the surface of a dielectric substrate made of glass, ceramic, sitall (glass-ceramic), or sapphire, while the active elements are unpackaged semiconductor devices.
Film ICs - all elements and interconnections are made only in the form of films of conducting and dielectric materials
Secondary Power Supply Source
An SPS is an electronic device intended for converting alternating voltage into direct voltage of a required value.
To obtain electrical energy of the required type, it is necessary to convert alternating-current energy into direct-current energy using rectifiers, and direct-current energy into alternating-current energy using inverters.
Rectifiers and inverters are secondary power supply sources.
Let us consider a secondary power supply source that converts alternating-current energy into direct-current energy. Such secondary power supply sources (SPS) are needed to power various pieces of electronic equipment (DC motors, various amplifiers, chargers, etc.).
Rectification is the process of converting alternating current into direct current using rectifying devices that possess unidirectional conductivity. Rectifying devices consist of the following main blocks: a transformer, an electric valve (rectifying element), a smoothing filter, and a voltage regulator.
Modern electronic semiconductor devices, in discrete form and especially in microelectronic form, impose very strict requirements on the quality of the consumed power, which must be highly stable
Classification of SPS units
1. Uncontrolled (diode-based), controlled (thyristor-based).
2. By the number of phases of the supply AC voltage: single-phase, three-phase
3. By the shape of the rectified voltage: half-wave, full-wave (bridge, or with a transformer center tap).
Single-phase low-power rectifying devices are used to power DC loads with a power from 1 W to 1 kW. Accordingly, this type of power source is called a low-power secondary power supply source (LPSPS).
Let us examine the block diagram of an LPSPS device, Fig. 1.
Fig. 1. Block diagram of an LPSPS
Description of the operation of the main LPSPS blocks
At the input, the transformer (Tr) converts the AC voltage Us to the required value U2, i.e., it matches the input voltage with the load and provides electrical isolation between the rectifying-voltage source and the load device.
After the transformer comes the diode valve group (V), where U2 is converted into a pulsating voltage Up. The number of valves depends on the rectifier circuit.
In the rectified voltage Up, besides the DC component there is also an AC component, which is reduced to the required level U by means of a smoothing filter (Sf) and has very small ripple.
The voltage regulator (Reg) keeps the voltage Uload constant across the load device Rload.
Depending on operating conditions, some blocks may be absent (the transformer or the regulator).
Two types of rectifiers are used to rectify single-phase alternating voltage: half-wave and full-wave
Half-wave rectifier
It is assumed that the transformer and the rectifying diode are ideal, i.e., the transformer's winding resistance is zero, and for the diode Rfwd = 0 and Rrev = ∞.
Fig.2 Half-wave rectifier circuit
Operating principle of the rectifier
Let us examine the timing diagrams of the half-wave rectifier (Fig.3): in the time interval 0 - T/2, diode VD1 is open, φA > φB, and current iload flows in the load.
In the time interval T/2 - T, the diode is closed, φA < φB, and U2m is applied across the diode.
Fig.3. Timing diagrams of the half-wave rectifier
The current and voltage in the load are pulsating in nature and, as a result, differ significantly from their DC (average) components
Main electrical parameters of a rectifier
The diode is the main element in rectifiers and largely determines the rectifier's main performance figures.
1. Uload,avg and Iload,avg - the average values of the rectified voltage and current in the load device
2. Power of the load device Pload,avg = Uload,avg•Iload,avg
3. Amplitude of the fundamental harmonic Ufund
4. Ripple factor of the rectified voltage
5. Rectifier efficiency
6. Maximum reverse voltage across the blocked diode Urev max
Let us determine the average value of the rectified voltage and current in the load.
In a half-wave rectifier, more than half of the input voltage is lost!
Input voltage (voltage across the transformer's secondary winding):
The average value of the rectified current - the average rectified current is equal to the current through the diode:
The ripple frequency of the rectified voltage equals the frequency of the mains voltage:
fp = ffund
The rectified voltage has a non-sinusoidal waveform, so it can be expanded in a Fourier series:
Since the ripple frequency of the rectified voltage equals the mains frequency, the voltage of the fundamental (first) harmonic is used when calculating the ripple factor:
p = 1.57 - a very large ripple factor, which is a drawback of this circuit.
The maximum reverse voltage across the blocked diode equals the amplitude of the input voltage:
When selecting rectifier diodes, the maximum permissible parameters are used: the maximum permissible forward current and the maximum permissible reverse voltage: Ifwd max, Urev max.
The diode is the main element in rectifiers, and its parameters largely determine the rectifier's main parameters
Full-wave bridge rectifier
Fig.1 Full-wave bridge rectifier
Operating principle of the bridge rectifier
The diode bridge circuit is connected to the transformer's secondary winding, Fig.1,
each pair of diodes operates alternately - VD1,VD3 and VD2,VD4: in the timing diagrams, Fig.2
in the time interval 0-T/2, VD1,VD3 are open, VD2,VD4 are closed, and current Iload flows in the load;
in the time interval T/2-T, VD1,VD3 are closed, VD2,VD4 are open, and current Iload flows in the load;
the ripple frequency of the rectified voltage is twice the mains frequency
fp = 2fs = 100 Hz.
Fig.2. Timing diagrams of the bridge rectifier
Main parameters of the bridge rectifier
1. Average rectified voltage:
2. Average rectified current:
Forward current of the diode:
3. Expanding the voltage across the load in a Fourier series, we obtain the numerical value of the ripple factor for the bridge rectifier circuit:
Amplitude of the fundamental (second) harmonic with frequency 2ω:
Consequently, the ripple factor will be equal to:
The maximum reverse voltage on each of the closed diodes has the same value as in the half-wave rectifier, since with respect to the input they are connected in parallel:
U2m = √2U2;
Urev max = π•Uload,avg; Urev max = √2U2
The main drawback is the large number of diodes.
Nowadays semiconductor rectifier bridge assemblies are manufactured (KTs402, KTs403, and others
Smoothing filters
At the output of a rectifier, a pulsating DC voltage is obtained. For many electronic devices, the ripple factor of the supply voltage must not exceed p = 10-2 - 10-5. Therefore, smoothing filters are used to reduce the ripple.
Filters are usually built on reactive elements: capacitors and inductors (chokes). This makes use of the reactive properties of these elements: connected in series, a choke has high resistance to alternating current; connected in parallel, a capacitor has low resistance to alternating current. A feature of filters is that a capacitive filter smooths ripple better at small load currents, while an inductive filter, on the contrary, works better at large currents.
A capacitive filter is always connected in parallel with the load. Let us examine a half-wave rectifier with a smoothing capacitive filter, Fig.3.
Fig. 3 Circuit of a half-wave rectifier with a capacitive filter
The smoothing principle can be summarized as follows (Fig.4) for the circuit in Fig.3: in the first half-period (0 - T/2), when the potential of point A is higher than the potential of point B, diode VD1 is open and the capacitor charges through the diode's low internal resistance up to U2max. When the potential of point A becomes lower than the voltage on the capacitor, during the second half-period (T/2 - T) the diode is closed and the capacitor discharges through the load resistor Rload, until the potential of point A again exceeds the voltage on the capacitor.
Fig. 4 Voltage timing diagrams of a half-wave rectifier with a capacitive filter
The voltage across the blocked diode is determined using Kirchhoff's second law:
Urev max = Uc + U2max
and since the capacitor charges up to the value U2max, it follows that:
for a half-wave rectifier:
Urev max = 2•U2max = 2√2 U2
for a full-wave rectifier:
Urev max = U2max = √2 U2
The average rectified voltage of rectifiers with a filter is determined by the formula
Full-wave bridge rectifier with smoothing capacitive filter
Let us examine a full-wave bridge rectifier with a smoothing capacitive filter, Fig.5.
Fig.5 Circuit of a bridge rectifier with a capacitive filter
Fig. 6 Timing diagrams of a bridge rectifier with a capacitive filter
From analyzing the timing diagrams (Fig. 4, Fig.6), it can be seen that as the capacitance of capacitor C changes, the value of the rectified voltage's ripple factor will change. Moreover, the less the capacitor discharges, the smaller the ripple in the rectified current Iload will be.
the discharge time constant of the capacitor: τdis = C•Rload.
If τdis >> T, then the ripple factor is calculated using the formulas:
for the half-wave circuit:
where: fs - the mains voltage frequency;
for the full-wave circuit:
where: fs - the mains voltage frequency.
To select a capacitor, its capacitance and operating voltage must be calculated.
The filter capacitance, in the case of small ripple, is determined by the formula:
for a half-wave rectifier
for a full-wave rectifier
The operating voltage of the capacitor is calculated with a 30% margin and equals:
Uop ≥ 1.3∙U2max
It should be taken into account that manufactured capacitors have a tolerance of ±12% of the nominal capacitance value.
The main parameter characterizing the effectiveness of an electrical smoothing filter is the smoothing factor, equal to the ratio of the ripple factors at the filter's input and output. When designing filters, the following requirements must be met: minimal voltage drop across the filter elements, and minimal size and mass.
When using a capacitive filter, it should be taken into account that the maximum value of the current through the diode is determined only by this element's internal resistance, so it can reach values greater than the diode's maximum permissible forward current. Such a current can damage the diode. To avoid this, an additional series resistor is connected to the diode.
If a higher smoothing factor is required, more complex LC or RC filters are used. Connecting an inductor to the capacitive filter results in a significant reduction of the AC component's share of the rectified voltage, due to the voltage drop across the inductor, while the voltage drop from the DC component is practically zero. The only problem with using an inductor is that the mass and size of the LPSPS increase. Therefore, in an LPSPS a resistor Rf is used instead of an inductor Lf. The filtering action of Rf consists in the fact that, when Xc << Rload, a greater voltage drop of the AC component of the rectified voltage occurs across Rf than of the DC component.
The smoothing factor of the filter in this case will be:
So that the reduction of the DC component is not too large, Rload and Rf are chosen
to be comparable in magnitude:
If a smoothing filter cannot reduce the ripple of the rectified voltage to the required value, cascaded filters are used, in which case the smoothing factor is determined by the formula: S = S1•S2•S3•...Sn
External characteristics of rectifiers
The external characteristic of a rectifier is the dependence of the voltage across the load device on the current through it (Fig.10).
In a rectifier without a filter (Fig. 7, curve 1), the load voltage and current are related by: 
where Uload,oc is the output voltage of the rectifier in the open-circuit (no-load) mode, i.e., at Rload = ∞,
Rd - the internal resistance of the diode in the open (conducting) state,
Rtr - the resistance of the transformer winding.
In the rectifier (Fig. 7, curve 1), the output voltage in no-load mode will be Uload,oc; in the rectifier with a filter (Fig. 7, curve 2), the output voltage in no-load mode will be greater, and will equal the amplitude value of the input voltage, since with no load, the capacitor charges up to the amplitude value of the voltage on the transformer's secondary winding.
Fig.7 External characteristics of rectifiers
Three-phase rectifiers
Three-phase AC rectifiers are used as rectifiers of medium and high power. There are two main types of three-phase rectifiers: with a neutral tap and bridge-type.
Three-phase rectifier with a neutral tap
Fig. 1 Circuit of a three-phase rectifier with a neutral tap
Figure 2 shows the timing diagrams of the voltage u2(t) at points a, b, c, the current through resistor R, and diodes VD1, VD2, and VD3.
By Kirchhoff's first law, the current through the resistor equals the sum of the currents of all three branches, taking sign (direction) into account. Since, in this circuit, the currents in each phase are directed toward node d' whenever the potentials at points a, b, c relative to node d are positive, the total current through the resistor always has one and the same direction. That is, rectification of the current takes place.
Let us carry out a more detailed analysis of three-phase current rectification, Fig. 2.
Fig. 2 Timing diagrams of the potentials at points a, b, c - ua(t), ub(t), uc(t); the currents through the diodes iVD1, iVD2, iVD3, and the current through resistor iR.
At the moment t = 0, the potentials at points a and c are equal. As a result, the potential difference across the leads of diodes VD1 and VD3 is zero, so the current through these diodes at this moment is zero. The potential at point b relative to the potentials at a and c is negative, so the voltage across the leads of diode VD2 is reverse, and no current flows through VD2.
For 0 > t > t1, the potential difference across VD2 and VD3 corresponds to reverse voltage, since ua(t) > uc(t) > ub(t), while across VD1 it is forward. Therefore current begins to flow through VD1 and R, equal to .
The maximum current through the resistor will be observed at the moment t = t1. At t = t2, the potentials at points a and b equalize, and the current through diodes VD1 and VD2 stops because the potential difference becomes zero. The current through diode VD3 is zero because the potential at point c is negative, and the voltage across it, equal to the potential difference between point c and points a and b, is reverse.
In the intervals from t2 to t3 and from t3 to t4, a similar situation occurs for iVD2 and iVD3. The current through the resistor over time consists of a sequence of currents through diodes VD1, VD2, and VD3.
In a three-phase rectifier with a neutral tap, the ripple factor p = 0.25.
The average values of the rectified voltage and current are given by the following expressions:
The maximum reverse voltage on the diodes equals the potential difference between points (a-c)-b, (a-b)-c, and (b-d)-a at the moments t0, t1, 
. The potential difference at these moments across diodes VD1, VD2, VD3, respectively, and so on, equals:
This type of rectifier allows obtaining rectified currents of up to hundreds of amperes, with the rectified voltage reaching several tens of kilovolts. The main drawback is the DC magnetization of the transformer core, which reduces the rectifier's efficiency
Three-phase bridge rectifier
Fig. 3 is superior in all respects to the three-phase rectifier with a neutral tap. It is used for converting currents and voltages of medium and high power.
This rectifier contains a bridge of six diodes. During each 1/6 of the period, one pair of diodes is under the action of forward line voltage, while the other four diodes are under reverse voltage.
For example, starting from moment t0 until moment t1, diodes VD1 and VD4 are under forward voltage, since phase a has a positive potential that opens VD1 and closes VD2, while phase b has a negative potential that opens diode VD4 and closes VD3. The potential difference between phases a and b during this period is greater than the potential difference between phases a and c and b and c, so diodes VD2, VD3, VD5, and VD6 are closed and do not conduct current.
In the following time period, from t1 to t2, the greatest line voltage occurs between phases a and c. The potential of phase a keeps diode VD1 open and VD2 closed, while the negative potential of phase c opens diode VD6 and closes diode VD5. The remaining diodes are closed because of the smaller potential difference between phases a and b and b and c.
Fig. 3 Three-phase bridge rectifier
and timing diagrams of the rectified voltage and currents.
Next, the following pair of diodes is switched on and the other four are switched off. That is, during the corresponding periods of time, the diodes conducting in the forward direction are those to which the largest line voltage is applied.
Obviously, the average values of current and voltage for this rectification circuit are the largest among the circuits considered.
Parametric voltage stabilizer
In many electronic devices that use secondary power supply sources, there is an obligatory requirement to maintain the voltage or current at a certain constant level, regardless of possible changes in the input voltage and output current. To fulfill this task, voltage or current stabilizers are used. In this instructional manual we consider a parametric voltage stabilizer based on a semiconductor zener diode. Parametric stabilizers have a simple design and high reliability, but low efficiency.
The circuit of the parametric voltage stabilizer, Fig. 4, consists of a ballast resistor Rballast (to limit the current through the zener diode) and a zener diode connected in parallel with the load, which performs the main stabilizing function.
Fig. 4 Circuit of the parametric voltage stabilizer
The basic relationships between the currents and voltages in the stabilizer are determined by Kirchhoff's first and second laws:
Operating principle of the parametric stabilizer
The operating principle of a parametric DC voltage stabilizer is conveniently explained using Fig. 5, which shows the current-voltage characteristic (I-V curve) of the zener diode and the "flipped" I-V characteristic of the ballast resistor. The voltage stabilizer operates as follows. When the input voltage U of the stabilizer changes, there is a corresponding change in current I, and consequently the currents of the zener diode and the load change. However, when the zener diode's current changes, the voltage across it changes only by a very small amount, in accordance with the zener diode's I-V characteristic (Fig.5), i.e., it remains almost unchanged. According to Kirchhoff's second law, when the input voltage changes, the voltage drop across the ballast resistor changes proportionally to the current, and turns out to be equal to the increment of the input voltage. In other words, the entire increment of the input voltage falls across the ballast resistance, while the voltage across the zener diode and the load remains almost unchanged. Let us express this mathematically:
U ± ∆U = (Ist + Iload ±∆Ist)•Rballast + Uload
Taking U = const and Rload = const, we obtain Iload = const, while the condition for keeping the zener diode's operating point on segment AB of the I-V characteristic (Fig.5) is determined by the formula:
±∆U = ±∆Ist•Rballast
Fig. 5. Explanation of the operating principle of the voltage stabilizer
It follows from this that normal operation can be ensured by the appropriate choice of the ballast resistance value. Then, when the voltage at the stabilizer's input changes, the normal limits of stabilization of the output voltage Uload are not violated.
When stabilizing voltage, taking Iload = var and Rload = var and U = const, at the stabilizer's input there occurs a redistribution of currents between the load and the zener diode, while the voltage across the zener diode and the voltage drop across the ballast resistance remain unchanged, in accordance with the equation:
U = I•Rballast + Uload = ((Iload ± ∆Iload) + (Ist ± ∆Ist))•Rballast + Uload
For the stabilizer to operate normally under a changing load, the change in current must not cause the zener-diode current to go outside the maximum and minimum permissible limits.
Under the condition U = const and Rload = const, designing the stabilizer amounts to choosing the zener diode and choosing the value of Rballast; then from the system of equations (1) we obtain the formula for calculating Rballast:
The resistance value must be such that the zener-diode current is not less than Ist min, i.e., does not go outside the operating segment AB (Fig.5) of the zener diode's I-V characteristic.
The ballast resistance accounts for the main losses of the stabilizer, so parametric stabilizers are used only in low-power circuits.
The zener diode is selected by parameters from a reference handbook:
1. Ist max - the maximum permissible zener-diode current;
2. Ust - the stabilization voltage;
3. Ist min - the minimum zener-diode current.
Main parameters of the stabilizer:
1. Stabilization coefficient, equal to the ratio of the increments of the input and output voltages. The stabilization coefficient characterizes the quality of the stabilizer's operation.
2. Output resistance of the stabilizer
Rout = Rdiff
To find Kst and Rout, an equivalent circuit of the stabilizer for increments is considered, Fig.6. The nonlinear element operates in the stabilization region, where its AC resistance Rdiff is a parameter of the stabilizer.
Fig. 6 Equivalent circuit of the parametric voltage stabilizer
The differential resistance Rdiff is determined from the equation:
For the equivalent circuit, taking into account that Rload >> Rdiff and Rballast >> Rdiff, we obtain the stabilization coefficient:
The stabilization coefficient of a parametric voltage stabilizer Kst = 5 ÷ 30
To increase the stabilized voltage, zener diodes are connected in series.
Connecting zener diodes in parallel is not permitted. To increase the stabilization coefficient, several parametric voltage stabilizers can be cascaded
Transistors
Bipolar, field-effect, IGBT.
Bipolar transistors
A bipolar transistor is a three-layer semiconductor n-p-n or p-n-p structure intended for amplifying the power of electrical signals.
The diagram of the technological structure of a bipolar transistor and its symbols are shown in Fig. 1.
Fig. 1 Diagrams of the technological structures of bipolar transistors
and their symbols.
Internal structure of the transistor
Transistor connection configurations
The three layers mentioned have the following names: emitter (E), base (B), collector (C). To amplify electrical power, three configurations for connecting a bipolar transistor are used: common emitter (CE), common base (CB), and common collector (CC).
Fig 2 Transistor connection configurations
Transistor operating modes
1. Active (amplifying) mode
2. Saturation mode
3. Cutoff mode
Static current-voltage characteristics of a BJT
Fig 3
Amplifying properties of the transistor
common-emitter transistor configuration
Proof: let
The transistor is controlled by the base current
Equivalent circuit of a bipolar transistor
Fig 4
The relationship between the input and output currents and voltages in the transistor, represented as an equivalent two-port network, is expressed by a system of equations of electrical state:
h - transistor parameters
input resistance of the transistor
feedback coefficient
DC current gain
output conductance
One of the main parameters of a bipolar transistor is the current transfer ratio. When operating in DC mode, for the common-base configuration this is the ratio of the collector current to the emitter current
For the common-emitter configuration, the DC current transfer ratio equals the ratio of the collector current to the base current
In addition, as with any two-port network, the other main parameters of the transistor are its input and output resistances, which characterize how well the transistor's input and output circuits are matched with other two-port networks.
Graphical determination of the transistor's h-parameters
Uce = Ec - Ic•Rc - the load line
Table 1 gives comparative parameters of these connection configurations.
Field-Effect Transistors (FETs)
A field-effect transistor is a semiconductor device whose amplifying properties are due to a flow of majority charge carriers passing through a conducting channel controlled by an electric field.
The current is determined by the movement of majority carriers of only one type of charge.
Field-effect transistor electrode names
Source – the electrode through which charge carriers flow into the conducting channel;
Drain – the electrode through which charge carriers flow out of the conducting channel;
Channel – the region in the semiconductor where the flow of majority charges is regulated;
Gate – the electrode to which an electrical signal is applied to control the value of the current through the conducting channel.
Types of field-effect transistors
1. Junction field-effect transistor (JFET)
n-channel
p-channel
2. MOS (MOSFET) transistors
With a built-in (depletion) channel
With an induced channel
Circuit configurations for field-effect transistors
Common-source configuration
Current-voltage characteristics of a field-effect transistor
with a p-n junction gate
Main parameters of an FET
• Transconductance of the drain-gate characteristic
at Uds = const
S = (∆ Id /∆ Ugs)
• Differential drain (channel) resistance in the saturation region
at Ugs = const
Rd = (∆Uds /∆ Id)
Parameters of field-effect and bipolar transistors
Parameters
IGBT – power transistors
Insulated Gate Bipolar Transistor – a new class of power devices that combine the advantages of bipolar and field-effect transistors.
Current control in such devices is achieved by the voltage applied to the gate.
The IGBT was first developed in the research laboratory of General Electric and brought to market by Motorola.
An IGBT is essentially a bipolar p-n-p transistor controlled by a low-voltage MOS field-effect transistor with an induced channel, through a high-voltage n-channel.
IGBT symbol
Operating principle
The turn-on process of an IGBT can be divided into two stages: after a positive voltage is applied between the gate and the source, the field-effect transistor turns on (an n-channel forms between the source and drain). The movement of charges from the n-region to the p-region causes the bipolar transistor to turn on and current to flow from emitter to collector. Thus, the field-effect transistor controls the operation of the bipolar transistor.
• The power of the signal applied to the gate of such a device is much smaller than in bipolar transistors, which allows the use of less powerful control circuits.
• Thanks to their high switching speed, these devices allow an increase in the operating frequency of power systems, thereby improving efficiency and size/weight characteristics, i.e., solving problems of energy and resource conservation
Thyristors
A thyristor is a semiconductor device based on a single crystal with a four-layer structure containing three p-n junctions, possessing valve-like (rectifying/switching) properties, i.e., a device that allows current to flow in one direction, with the ability to control its average and RMS value by controlling the turn-on phase of the thyristor.
Thyristor symbol
The control electrode allows the moment of thyristor turn-on to be controlled even when the potential difference between the anode and cathode is positive but smaller than the breakdown value, provided a forward current is created through the 1st p-n junction. The turn-on moment, or turn-on phase, is called the control angle.
Classification of thyristors:
• Diac (dinistor) – without a control electrode; only anode and cathode
• Thyristor proper (trinistor) – with a control electrode
• Triac – a bidirectional thyristor.
Operating principle
Let us consider the operating principle of a thyristor.
When a voltage Uin is applied to the anode of the thyristor, junctions J1 and J3 are open while junction J2 is closed, so all the input voltage is applied across the blocked layer J2. As a result, the thyristor current is very small. As the input voltage increases, the current through the thyristor increases slightly until junction J2 breaks down; the breakdown voltage is called the turn-on voltage
Uin = Ubr = Uon (point a). The segment |0a| is the reverse branch of junction J2. When junction J2 breaks down, the current through the thyristor increases sharply (point b). Along segment |bc| all three junctions are under the input voltage, since the voltages of junctions J1 and J3 are equal but opposite in sign. Segment |ac| is the "negative resistance" region of the thyristor.
If a current is applied to the control electrode, the breakdown voltage of the thyristor can be changed. The larger the control current, the lower the turn-on voltage of the thyristor, i.e., the thyristor turns on earlier.
Ictrl4 > Ictrl3 > Ictrl2 > Ictrl1 > 0, hence Uon4
Thyristor parameters:
• Uon – turn-on voltage
• Ictrl – control current
• Uctrl – control voltage
• ton – turn-on time
• toff – turn-off time
• Uon max, at Ictrl=0
An important parameter of a thyristor is the control current Ictrl – the current through the control electrode that switches the thyristor into the conducting state.
Advantages of the thyristor
Thyristors have found wide application due to a number of advantages compared with diodes:
• high specific power
• low internal losses, i.e., high efficiency
• wide range of operating temperatures (from –40 to +120 °C)
• instant readiness for operation
• short turn-on times and rapid recovery of blocking properties
Industry produces thyristors
• for currents I from 2 to 150 A
• for voltages U from 50 to 1000 V
Triac
A triac is a bidirectional (symmetrical) thyristor
It has a five-layer structure and exhibits thyristor-like characteristics for both polarities of the supply voltage.
Application
Widely used because it has two stable states – on and off – and its turn-on and turn-off times are shorter than those of diodes. It is used in power control devices in household appliances, in adjustable power supplies, in powerful pulse generators, in DC electric power transmission lines, in static reactive-power comparators, etc.
Triac I-V characteristic
Controlled rectifiers
Rectifiers that combine rectification of an alternating voltage with control of the rectified voltage are called controlled rectifiers.
The main element of a controlled rectifier is the thyristor.
Controlling the voltage amounts to controlling, in time, the moment when the thyristor turns on.
Classification of controlled rectifiers
• single-phase half-wave
• single-phase bridge: with a full complement of thyristors, and with a partial complement, i.e., 2 thyristors and 2 diodes
• three-phase, with a center-tapped transformer, and bridge type.
Half-wave controlled rectifier
CU – control unit. During the positive half-cycle of e(t), the control current opens the 1st p-n junction and turns on the thyristor. During the negative half-cycle, opening of the 1st p-n junction does not lead to opening of the 3rd p-n junction, because the diffusing carriers do not reach it, having almost completely recombined by that point.
The average and RMS value of the rectified current (voltage) can be adjusted over a wide range by changing the phase at which the control current is applied.
The circuit shown includes a control circuit, which significantly complicates it, since fairly precise synchronization of the frequency of the control current with the frequency of the rectified voltage is required.
Timing diagrams
Regulation of the average output voltage of a half-wave rectifier
the voltage can be adjusted within the range
by varying the control angle
for a full-wave rectifier
control characteristic of a controlled rectifier
Electrical signal amplifiers
Amplifier operating modes
Depending on the position of the operating point on the transistor's characteristic curves at quiescent state (with no input signal), as well as on the magnitude of the signal being amplified at the input, three main operating modes of amplifier stages, or amplification classes, are distinguished: A, B, and C. The main characteristics of these modes are nonlinear distortion and efficiency.
Mode A is characterized by the fact that the quiescent operating point is chosen in the middle of the linear section of the input and transfer characteristics (the dependence of collector current on base current). Since in mode A the dependence of collector current on base current is practically linear, nonlinear distortion is minimal. However, because the average value of the collector current is much greater than the amplitude of the amplified current, the efficiency of such amplifiers is low, not exceeding 50%.
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Часть 1 Electronics (Component Base and Operating Principles)
Часть 2 - Electronics (Component Base and Operating Principles)
Часть 3 - Electronics (Component Base and Operating Principles)
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