Triac inverter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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In practice, there are often cases when it is required to stop the process, say, heating, using the contact closure signal from the sensor. For example, in a samovar, I installed an emergency water boiling sensor from a car radiator, which closes the contacts when boiling. For several years he tormented me with his spark and induction interference, controlling the operation of an electromagnetic relay with a coil directly at 220 V and disrupting the operation of everything that is more complicated than a samovar. In search of the optimal solution, I came to this completely "wrong" scheme (Fig. 1), which, meanwhile, has been working for a long time and reliably, delighting the soul several times a day.
Ris.1
In the above circuit, there are no elements of the rectifier - the transistor itself performs these functions. Any transistor can be used, incl. and other conductivity (Fig. 2): MP38, MP42, KT315, P214, etc. - all the same, the circuit will work without power loss at a switching frequency of 100 Hz.
Ris.2
Of course, if reduced power is sufficient, you can simply replace the triac with a thyristor; and you can use the switching circuit shown in Fig. 3.
Ris.3
The value of the resistor R2 (Fig. 1) may have to be selected. To do this, with a connected load, you need to connect the control electrode of the triac to its anode through R2 (bypassing the transistor) and select the maximum resistance of the resistor at which the triac (thyristor) opens. Connecting a 220 V network indicating "phase" and "zero" is dictated by purely practical security considerations, this does not affect the operation of the circuit, HL1 is a gas discharge indicator (neon lamp or thyratron). R - quenching resistor (resistance is selected depending on what will be applied). When the triac is open, the indicator lights up at half its brightness (on indication), when closed, at full brightness (ready indication).
This circuit can be used in burglar alarm systems, but already using the reverse principle: the normal state is a locked triac (the security loop is closed). The current consumed by the circuit in the off state is only 3 ... 6 mA (depending on the quality of the transistor used), which is incomparably less than that of the currently existing security power systems with their semi-luminous incandescent lamps. If the integrity of the security alarm loop is violated, the circuit can turn on a rather powerful load, in which it is easy to come up with a blocking system for not turning off the power when trying to restore the loop contact. The current in the base circuit of the transistor is about 1 mA (depending on the quality of the transistor).
Author: V.Silchenko, Vikulovo village, Tyumen region; Publication: N. Bolshakov, rf.atnn.ru
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