Triac power regulator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Triac power regulator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

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In triac power controllers operating on the principle of passing a certain number of current half-cycles through the load per unit time, the parity condition for their number must be met. In many well-known amateur radio (and not only) designs, it is violated. Readers are offered a regulator that is free from this shortcoming. Its scheme is shown in Fig. one.

Triac power controller
Fig. 1

There is a power supply unit, an adjustable duty cycle pulse generator and a pulse shaper that controls the triac. The power node is made according to the classical scheme: current-limiting resistor R2 and capacitor C1, rectifier on diodes VD3, VD4, zener diode VD5, smoothing capacitor ud. the pulse frequency of the generator, collected on the elements DD1.1, DD1.2 and DD1.4, depends on the capacitance of the capacitor C2 and the resistance between the extreme terminals of the variable resistor R1. The same resistor regulates the duty cycle of the pulses.

Element DD1.3 serves as a pulse generator with the frequency of the mains voltage supplied to its output 1 through a divider of resistors R3 and R4, with each pulse starting near the transition of the instantaneous value of the mains voltage through zero. From the output of the DD1.3 element, these pulses are fed through the limiting resistors R5 and R6 to the bases of the transistors VT1, VT2. The control pulses amplified by the transistors through the decoupling capacitor C4 come to the control electrode of the triac VS1. Here, their polarity corresponds to the sign of the mains voltage applied at that moment to the pin. 2 triacs.

Due to the fact that the elements DD1.1 and DD1.2, DD1.3 and DD1.4 form two triggers, the level at the output of the DD1.4 element, connected to pin 2 of the DD1.3 element, is reversed only in the negative half-cycle of the mains voltage.

Suppose the trigger on the elements DD1.3, DD1.4 is in a state with a low level at the output of the element DD1.3 and a high level at the output of the element DD1.4. To change this state, it is necessary that the high level at the output of the DD1.2 element, connected to pin 6 of the DD1.4 element, becomes low. And this can only happen in the negative half-cycle of the mains voltage supplied to pin 13 of the DD1.1 element, regardless of the moment the high level is set at pin 8 of the DD1.2 element.

The formation of the control pulse begins with the arrival of a positive half-cycle of the mains voltage at pin 1 of the element DD1.3. At some point, as a result of recharging the capacitor C2, the high level at pin 8 of the DD1.2 element will change to low, which will set a high voltage level at the output of the element. Now the high level at the output of the DD1.4 element can also change to a low one, but only in the negative half-cycle of the voltage supplied to pin 1 of the DD1.3 element. Therefore, the operating cycle of the control pulse shaper will end at the end of the negative half-cycle of the mains voltage, and the total number of half-cycles of the voltage applied to the load will be even.

The main part of the device parts is mounted on a single-sided printed circuit board, the drawing of which is shown in fig. 2.

Fig. 2

Diodes VD1 and VD2 are soldered directly to the terminals of the variable resistor R1, and the resistor R7 is soldered to the terminals of the triac VS1. The triac is equipped with a factory-made ribbed heat sink with a heat-removing surface area of about 400 cm2.

Used fixed resistors MLT, variable resistor R1 - SPZ-4aM. It can be replaced by another of the same or greater resistance. The values of resistors R3 and R4 must be the same. Capacitors C1, C2 - K73-17. If increased reliability is required, then the oxide capacitor C4 can be replaced with a film one, for example, K73-17 2,2 ... 4,7 uF at 63 V, but the dimensions of the printed circuit board will have to be increased. Instead of KD521A diodes, other low-power silicon ones are also suitable, and the D814V zener diode will replace any more modern one with a stabilization voltage of 9 V.

Replacement of transistors KT3102V, KT3107G - other low-power silicon of the corresponding structure. If the amplitude of the current pulses opening the triac VS1 is insufficient, the resistance of resistors R5 and R6 cannot be reduced. It is better to choose transistors with the highest possible current transfer coefficient at a voltage between the collector and emitter of 1 V. For VT1 it should be 150 ... 250, for VT2 - 250 ... 270.

Upon completion of the installation, you can connect a load with a resistance of 50 ... 100 Ohm to the regulator and turn it on to the network. In parallel with the load, connect a DC voltmeter for 300 ... 600 V. If the triac steadily opens in both half-cycles of the mains voltage, the voltmeter needle does not deviate from zero at all or fluctuates slightly around it. If the voltmeter needle deviates only in one direction, then the triac opens only in half-cycles of one sign. The direction of the deflection of the arrow corresponds to the polarity of the voltage applied to the triac, at which it remains closed. Usually, the correct operation of the triac can be achieved by installing a transistor VT2 with a large value of the current transfer coefficient.

Author: V. Molchanov, Sineborsk, Krasnoyarsk Territory; Publication: radioradar.net

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