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CALCULATION OF THE PULSE STABILIZER
Гущин Иван Олегович, Харлашина Софья Вячеславовна, Сибирский государственный университет науки и технологий имени М. Ф. Решетнева, г. Красноярск
E-mail: kharlashina.v@mail.ru
Abstract. The work is presented the classification of thyristors according to such characteristics as the number of terminals, the type of output voltage-ampere (VAC) characteristics, the method of switching on and control, etc. Information on the use of thyristors as electronic keys is investigated. The case of using a thyristor as an alternating voltage rectifier is also considered.
Key words: thyristor, electronic key, voltage, rectifier.
In the process of automation and control of technological processes, telemechanics and communication, there is often a need for switching (disconnecting, connecting and switching) of electrical circuits. For these purposes, an electronic key is used - a device that has two stable states: low and high conductivity. Switching between these states is carried out by means of control electrical signals. To meet these requirements, a semiconductor device known as a thyristor is used. The main function of the thyristor is to close and open the load circuit when exposed to an external control signal.
Thyristors can be classified according to several criteria. Firstly, by the number of conclusions. There are diode thyristors, or dinistors, which have only two outputs -an anode and a cathode. There are also triode thyristors, or transistors, with three terminals - an anode, a cathode and a control electrode. And finally, there are four-electrode, or tetrode, thyristors that have two input and two output outputs.
Secondly, thyristors can be classified according to the type of volt-ampere characteristic (VAC). Some thyristors do not conduct current in the opposite direction.
In addition, thyristors can be classified by the method of switching on and control, as well as by other characteristics, for example, by power.
Thyristors can be divided into two categories: thyristors that conduct current in only one direction (thyristors with reverse conductivity, also known as thyristors-diodes), and symmetrical thyristors (also known as two-wire, triacs or triacs), which can be switched to the open state at any voltage polarity.According to the switching method, thyristors are divided into non-lockable (switching off is provided only by reducing the current to a value less than the holding current, or by switching off the anode voltage) and lockable (switching off is possible via the input control circuit).
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There are various ways to control thyristors, including thyristors, photothyristors, and optothyristors. Thyristors can be controlled by an external electrical signal via a control electrode, while photothyristors are controlled by an external optical signal, and optothyristors by an internal optical signal (LED and photothyristor are combined into one design). This classification implies that the thyristor can be controlled not only through the cathode p-n junction, but also through the anode. The presence of an internal PIC does not affect which of the emitters will enhance the injection of carriers when the control signal is applied.
As already noted when deriving the VAC equation, the control current is needed only until the thyristor is switched to the open state. After that, it is no longer required. That is, the control signal can be represented as a short-term pulse.
This article discusses conventional thyristors, which are of the non-lockable type. They can be transferred from the open state to the closed state by reducing the current to the value of Iud or by switching off the anode voltage. However, there are also lockable thyristors that are widely used and can be turned off by applying a reverse polarity voltage pulse to the control electrode.
Symmetric thyristors (triacs, triacs) are very useful for solving many practical problems. They have the same type of VAC when applying both forward and reverse voltage (Fig. 1). Thus, they can be used as electronic keys. These switches are widely used in many practical circuits, for example, in controlled rectifiers that allow you to regulate the current through the load.
Fig. 1
If an alternating voltage is applied to the anode of the thyristor, it performs the function of a rectifier, passing current only in positive half-cycles and creating a sequence of pulses. Each pulse opens the thyristor only at a certain point in time t1, when the switching voltage is reached. At this moment, the thyristor opens, the voltage on it drops, and the current through it and the load increases sharply.
At the end of the pulse, the voltage on the thyristor drops to zero, which leads to its shutdown. Adjusting the voltage on the control electrode allows you to change the level of the control current and, accordingly, the moment of switching on the thyristor and the duration of the current pulse. These parameters affect the average value of the current in the load and the power released by the thyristor during the period of operation.
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The second example is a sawtooth voltage generator (Fig. 2). In this scheme, the capacitor is charged relatively slowly through resistor R from an external voltage source E2. As long as the voltage on the capacitor UC is less than the switching voltage, the thyristor is closed. When Uc = Uon, the thyristor opens and the capacitor is quickly discharged through the small resistance of the thyristor itself and the load resistance. Thus, the current through the thyristor is limited by the load resistance. Upon reaching the end of the capacitor discharge, the current through the thyristor decreases to the holding current, which leads to its closure and the beginning of the capacitor charge cycle.
Fig. 2. Sawtooth Voltage Generator
For trinistors, the parameters of the control circuit are added to the number of the main parameters: Iu.The unlocking direct control current is the smallest control current required to turn on the thyristor; Uu.ot is the constant unlocking control voltage, that is, the control voltage corresponding to Iu.from; Iu.ot.i and Uu.ot.i -unlocking pulse current and control voltage; Iu.z.i and Uu.z.i - locking pulse current and control voltage, i.e. the smallest pulse values of current and voltage required to turn off the thyristor (for lockable thyristors).
Important parameters of thyristors are also the turn-on time of tvkl, the turn-off time of tvkl. the total capacity of the SBS, the maximum value of the pulsed forward current of Imp.max. The turn-on time of thyristors is usually several microseconds, and the turn-off time is tens of microseconds. This is due to the fact that it takes a certain amount of time to absorb the excess charge accumulated in the base regions, which is associated with the recombination process. In this regard, thyristors can only operate in the low-frequency range. The upper limit frequency of this range is indicated in reference books and is usually several kilohertz.
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