Bizator  /  Adverts  /  equipment and materials  /  industrial equipment  /  industrial equipment spare parts

The power semiconductors and cooling to them: diodes, diacs, thyristors, triacs, triacs, varicaps are given, triacs...

Offer type: salePublished: 08.04.2014
Seller:Pimenov Gennadij
Write a message
Address:Ukraine, Kyiv Oblast', Kyiv
Sell power thyristors and diodes ,are semiconductor devices fresh years, Kiev, Ukraine, SERPAN.
The principle of operation of thyristor
The thyristor is a power electronic is not fully controlled by the key. So sometimes in the technical literature it is called anoperational thyristor, which can signal to be translated only in the conducting state, i.e., be included. To disable it, (when working in DC), you must take special measures to fall forward current to zero.
Thyristor switch can conduct current only in one direction, and in the closed state is able to withstand both direct and reverse voltage.
The thyristor is a four-layer p-n-p-n structure with three conclusions: anode (A) cathode (C) and the control electrode (G), as shown in Fig. 1
Fig. 1. Conventional thyristor: a) quasi - graphical notation; b) - V characteristic.
Figure 1, b presents the collection of the output of the static I-V characteristics at different values of drive current iG. Limit direct voltage, which is maintained by the thyristor without its inclusion, has a maximum value when iG = 0. With increasing current iG direct voltage, withstand the thyristor is reduced. Enabled state of the thyristor corresponds to the branch II, off - branch I, the process of inclusion - branch III. Holding current or a current deduction equal to the minimum acceptable value of the direct current iA , in which the thyristor remains in a conducting state. This value also corresponds to the minimum possible value of the direct voltage drop on the thyristor .
Branch IV represents the dependence of the leakage current from reverse voltage. When exceeding the reverse voltage value UBO begins a sharp increase of the reverse current, associated with the breakdown of the thyristor. Character breakdown can match irreversible process or the process of avalanche breakdown characteristic of the operation of semiconductor Zener diode.
Thyristors are the most powerful electronic key capable of switching circuits with a voltage up to 5 kV and currents up to 5 kA at a frequency of not more than 1 kHz.
The design of the thyristors shown in Fig. 2.
Fig. 2. Body construction thyristors: (a) tablet; b) pin
The thyristor circuit DC
The inclusion of conventional thyristor is performed by applying the pulse current in the control circuit is positive relative to the cathode polarity.For the duration of the transition process enabling significantly influenced by the nature of the load (resistive, inductive, etc.), amplitude and slew rate of the pulse drive current iG , the temperature of the semiconductor structures of the thyristor, the applied voltage and the load current. In the circuit containing the thyristor, should not have invalid values slew rate forward voltage duAC/dt, which can occur spontaneously turning on the thyristor in the absence of the control signal iG and rate of rise of current diA/dt. At the same time, the steepness of the control signal should be high.
Among ways off thyristors taken to distinguish between natural off (or natural commutation) and forced (or artificial switching). Natural commutation occurs when the thyristors in AC circuits at the moment of decay of the current to zero.
Types of forced commutation is very diverse. The most typical of them are the following: connecting the pre-charged capacitor With the S key (Fig 3, a); connect LC-circuit with a pre-charged capacitor CK (figure 3 b); the use of oscillatory nature of the transition process in the load circuit (figure 3).
Fig. 3. Methods of artificial commutation of thyristors: (a) by a charged capacitor; b) through oscillatory discharge LC-circuit; - due to the oscillatory nature of the load
When switching diagram in Fig. 3,and the connection of the switching capacitor with opposite polarity, such as other auxiliary thyristor to cause his discharge on conductive main thyristor. Since the discharge current of the capacitor is directed opposite to the direct current of the thyristor, the latter is reduced to zero and the thyristor turns off.
In the diagram in Fig. 3 b connecting the LC-circuit causes the oscillatory discharge of the commutating capacitor SC. In the beginning of the discharge current flows through the thyristor counter direct current, when they become equal, the thyristor is turned off. Further, the current LC-circuit switches thyristor VS in the diode VD. While through the diode VD is the loop current, the thyristor VS is the applied reverse voltage equal to the voltage drop across an open diode.
In the diagram in Fig. 3,the turn-on of thyristor VS on a complex RLC-load will cause the transition process. When a specific load, this process may have an oscillatory character with changing the polarity of the load current IR. In this case, after turning off the thyristor VS to turn on the diode VD, which begins to conduct current of the opposite polarity. Sometimes this switching method is called quasielectrons, as it is associated with a change in polarity of the load current.
The thyristor in the circuit of AC
When turning on the thyristor in the circuit of AC you can perform the following operations:
• enabling and disabling the electrical circuits with active and active-reactive load;
• the average and current values of the current through the load due to the fact that it is possible to adjust the time of filing of the control signal.
As thyristor key capable of conducting an electric current in one direction only, to use thyristors AC applied their counter-parallel (Fig. 4,a).
Fig. 4. Counter-parallel thyristors (a) and the form of the current under resistive load (b)
Average and effective values of the current range by changing the date of filing of the thyristors VS1 and VS2 opening signals, i.e., by changing the angle and (Fig. 4,b). The value of this angle for the thyristors VS1 and VS2 when the regulation is changed simultaneously by the control system. The angle is called the angle control or firing angle of the thyristor.
The most widely used in power electronic devices received phase (Fig. 4,a,b) and pulse-width control thyristors (Fig. 4).
Fig. 5. Type of voltage at the load when: (a) phase control thyristor; b) phase control thyristor with forced commutation;) - pulse-width control thyristor
When the phase control method thyristor with forced switching regulation of the load current as possible by changing the angle α and angle θ. Artificial switching is carried out using special nodes or when using a fully managed (lockable) thyristors.
When pulse-width control (pulse-width modulation - PWM) within the time Totcr on thyristors filed a control signal that they are open and to load the applied voltage Unom. During the time Tsacr control signal is absent and the thyristors are in non-conductive condition. The effective value of the current in the load
where In.m. - load current when Tsacr = 0.
The curve of the current in the load phase control of thyristors of nesinusoidal, which causes distortion of the mains voltage and the disruptions to consumers, sensitive to high frequency interference is a so-called electromagnetic incompatibility.
Lockable thyristors
Thyristors are the most powerful electronic key used for switching high-voltage and high-current (sinnatamby) circuits. However, they have a significant disadvantage - lack of controllability, which is manifested in the fact that they are off it is necessary to create conditions for reducing the direct current to zero. This in many cases restricts and complicates the use of thyristors.
To address this shortcoming developed thyristors, lockable signal on the control electrode G. Such thyristors call lockable (GTO - Gate turn-off thyristor) or docoperations.
Lockable thyristors (GTO) have a four-layer p-n-p-n structure, but at the same time have a number of significant design features that make them fundamentally different from the traditional thyristor - property of complete controllability. Static I-V characteristics lockable thyristor in the forward direction identical I-V characteristics of conventional thyristors. However, large block reverse voltage of the GTO are generally unable and often connected with the counter-parallel connected diode. In addition, for lockable thyristors characterized by a significant drop in the forward voltage. To deactivate the lockable thyristor must be submitted to the circuit of the control electrode powerful pulse of negative current (approximately 1:5 in relation to the value of the turn off direct current), but short duration (10-100 μs).
Lockable thyristors also have a lower maximum voltages and currents (approximately 20-30 %) compared with conventional thyristors.
The main types of thyristors
In addition to the lockable thyristors developed a wide range of thyristors different types, different performance, process control, direction of currents in a conducting state, and so on, Among them one should mention the following types:
thyristor-diode, which is equivalent to a thyristor with a counter-parallel connected diode (Fig. 6.12,a);
diode thyristor (dynistor), which goes into a conductive state when exceeding a certain level of voltage applied between a and C (Fig. 6,b);
the GTO (Fig. 6.12,c);
symmetric thyristor or triac, which is the equivalent of two anti-parallel connected thyristors (Fig. 6.12,d);
high-speed inverter thyristor (time off 5-50 µs);
the thyristor with the field control by the control electrode, for example, based on the combination of the MOS transistor with the thyristor;
obliterator controlled luminous flux.
Fig. 6. Conditionally graphic symbol of thyristors: a) - thyristor-diode; (b) diode thyristor (dynistor); c) the GTO; d) - triac
Protection thyristors
Thyristors are devices that are critical to RMS