Triac thermostat. Encyclopedia of radio electronics and electrical engineering

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

 Comments on the article

The difference between this version of the thermal stabilizer and many others previously described in our journal lies mainly in the replacement of the traditional trinistor with a triac, which made it possible to eliminate the rectifier bridge, made up of powerful diodes. As a result, the number of elements installed on the heat sink with an output power of up to 1 kW was reduced from five to one. The temperature stabilizer can be used to maintain the temperature in a house on a garden plot, in a cellar, a balcony "vegetable store" and other enclosed spaces.

Temperature stabilization by the proposed electronic device is carried out, as usual, by turning on and off the mains voltage supplied to the load - heater, depending on the temperature of the sensor - thermistor. The switching on of the triac itself occurs near the moment when the mains voltage passes through "zero", which reduces the level of interference.

The heat stabilizer circuit is shown in fig. 1. The temperature stabilizer uses a power supply unit and pulse formation circuits at the moments when the mains voltage passes through "zero", described in [1], so the part of the circuit that completely repeats Fig. 1 [1], not shown here.

"zero" a pulse of negative polarity is formed. The Schmitt trigger, assembled on the elements DD1.1, DD1.2 and the resistor R9, forms steep fronts and falls of this pulse. The positive voltage drop corresponding to the beginning of the half-cycle is differentiated by the C4R11 chain and is fed to the input terminal 12 of the DD1.4 element in the form of a short pulse of positive polarity.

At the same time, the second input (pin 13) of the DD1.4 element receives a signal from the output of the op-amp DA1, which acts as a comparator. Its inputs are connected to the outputs of a thermally sensitive bridge formed by resistors R5 - R8 and thermistor RK1. While the temperature of the thermistor is higher than that set by resistor R5, the voltage at the non-inverting input of the op-amp is less than at the inverting one, a low level signal is generated at the output of the comparator. At this time, the pulses do not pass through the DD1.4 element and the HL1 LED is closed.

When the temperature of the thermistor RK1 drops and the voltage across it becomes larger, the output signal of the op-amp will correspond to a high level, the HL1 LED will turn on, pulses from the differentiating circuit C4R11 will begin to pass through the DD1.4 element to the base of the transistor VT3. At the beginning of each half-cycle, the transistor will turn on the triac VS1 and thereby connect the load - the heater - to the network.

All elements of the device, except for the triac and the female part of the output connector X1, are mounted on a printed circuit board with dimensions of 80x50 mm (Fig. 2). The board, made of one-sided foil fiberglass, is designed for the installation of MLT resistors, capacitors K73 - 16 (C1), K50 - 6 (C2), KM - 5 (the rest). Variable resistor R5 - SDR - 4aM or SDR - 4bM. Diodes VD1 and VD2 - any silicon pulse or rectifier, zener diode VD3 - for a stabilization voltage of 10 ... 12 V. The K561LA7 microcircuit is replaceable by K176LA7 or KR1561LA7. Transistors VT1 and VT2 can be any low-power silicon pnp structures, transistor VT3 - medium or high power of the same structure with a permissible collector current of up to 150 mA.

The function of a comparator (DA1) can be performed by almost any op-amp operating at a full supply voltage of 10 V and consuming a current of not more than 5 mA, for example, KR140UD7, K140UD6, KR140UD6, KR140UD14. LED HL1 - any of the AL307 series. It should be taken out of the board as much as possible, and it should “look” in the same direction as the shaft of the variable resistor R5. The body of the resistor R5 is connected to the negative conductor of the microcircuit power circuit, which is necessary for its shielding.

The RK1 thermistor used in the manufactured sample of the device is MMT - 4. But any other MMT or KMT series with a nominal resistance of 10 ... 33 kOhm is also suitable. Better - sealed MMT - 4 or KMT - 4 [2, 3].

To determine the resistances of resistors R5 and R6, it is necessary to set the temperature range in which the thermostat must operate. The resistance of the thermistor is measured at the maximum operating temperature. The resistor R6 should have the same resistance or slightly less. Then the resistance of the thermistor is measured at the minimum temperature and the resistance of the resistor R5 is selected so that it, in total with the resistance of the resistor R6, is not less than the measured one. If there are difficulties in measuring the resistance of the thermistor in the temperature range, we can assume that for MMT series resistors it increases by 19% with a decrease in temperature by 5 ° C, by 41% with a decrease by 10 ° C and twice - by 20 ° C. Similarly, with the same increase in temperature, the decrease in the resistance of the device is 16%, 29%, and two times, respectively. For KMT thermistors, such a change is approximately 1,5 times greater.

The ratings of resistors R5, R6 and thermistor RK1 indicated in the diagram correspond to the temperature stabilizer operating range of 15 ... 25 ° С.

The circuit board and triac KU208G (or KU208V), mounted on a ribbed heat sink with dimensions of 60x50x25 mm, are placed in a plastic box with dimensions of 150x95x70 mm so that the thermistor is close to the bottom wall of the box, and the heat sink of the triac is to the top. Previously, in these walls of the smallest case, the largest possible number of ventilation holes with a diameter of 6 mm is drilled in increments of 10 mm. The LED and the resistor shaft are led out through the holes in the front wall of the box. The shaft of the variable resistor itself and the fixing screw of the plastic handle on it should not be accessible for accidental touch.

To adjust and calibrate the regulator begin without a triac. Pin 12 of element DD1.4 is temporarily connected with a wire jumper to pin 14 of this chip, and a DC voltmeter is connected to resistor R12. Capacitor C1 is shunted with a resistor of 220 ... 330 Ohm, after which the thermostat is connected to a DC source with an output voltage of 12 ... 15 V. The voltage value of this source is set so that the current consumed by the thermostat is within 18 ... 20 mA.

The thermistor is placed in water, the temperature of which corresponds to the middle of the operating range. The thermistor insulator must not touch water. When the shaft of the resistor R5 rotates clockwise, the HL1 LED should light up, and the voltmeter should show a voltage of about 9 V, while rotating it in the opposite direction, the LED will go out, and the voltmeter needle should be at the zero mark of the scale. Make an appropriate mark on the scale of the variable resistor. By changing the temperature of the water, the thermostabilizer is completely calibrated.

To carry out this operation, instead of a thermistor, you can use fixed resistors with ratings corresponding to the measured resistance of the thermistor at given temperatures.

After removing the additional resistor and wire jumper, the stabilizer is completely assembled and its operation is checked with an incandescent lamp connected to the X1 "Load" connector.

To linearize the scale of a variable resistor, you can use the recommendations of the article [4].

The regulator is installed in a vertical position so that the ventilation holes in its body are not covered by anything, for example, on the wall of the room. If the thermostat is used to maintain the temperature in the cellar, incubator or balcony "vegetable store", it is better to place it outside the thermostabilized volume, and take the thermistor out of the stabilizer case. In this case, to reduce the effect of pickups on the thermistor's place, an oxide capacitor with a capacity of at least 50 μF for a rated voltage of at least 10 V should be placed on the board. The thermistor itself and the wires leading to it must be carefully insulated.

The thermostat has no temperature hysteresis, and its accuracy can be very high - about 0,1°C. But if, for some reason, hysteresis is still required, it is necessary to connect a resistor between terminals 3 and 6 of the op-amp DA1 (in Fig. 2 it is shown by dashed lines) with a resistance of several megaohms.

Literature

1. Biryukov S. Triac power regulators. - Radio, 1996, No. 1, p. 44-46.
2. Thermistors. Educational poster. - Radio, 1975, No. 5. With. 32.
3. Resistors. Directory. - M.: Radio and communication, 1991, 528 p.
4. Aleshin P. Linearization of the thermistor bridge. - Radio, 1997, No. 11, p. 58, 59.

Author: S. Biryukov, Moscow

See other articles Section Power regulators, thermometers, heat stabilizers.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive Camel milk will be medicine 18.06.2012 Researchers have learned how to create transgenic camel embryos, which in the future will make it possible to obtain milk from these animals enriched with various therapeutic proteins. The ability of camels to adapt to extreme environmental conditions and their resistance to disease have made these animals an integral component of desert cultures. Scientists at the Dubai Camel Reproduction Center believe that with a little human help, camels could become a source of cheap medicine. They have developed a method to create transgenic camel embryos whose cells carry genes very similar to those of humans. Currently, researchers are working to increase the likelihood of successful implantation of such embryos and the birth of full-fledged camels. The next stage of work will be the introduction of human genes into the cells of genetically modified embryos. Scientists believe that the step they have taken is decisive, and everything else is a matter of technology. In addition to human genes, they plan to learn how to introduce genes from other species, such as cows, into the camel genome, which will increase the amount of lactation. Currently, therapeutic proteins such as insulin are produced using bacterial cultures in the laboratory. Getting them as part of camel milk will significantly reduce production costs and increase the availability of medicines for people around the world. The developers believe that they will need about five more years to launch the mass production of curative camel milk. It is also noted that, perhaps in the future, the developed approach will turn camels into ideal candidates for growing human organs for transplantation.

Other interesting news:

▪ Tram without rails

▪ inflatable bridge

▪ The sound of wagons generates energy

▪ Ceres tilted 36 degrees

▪ Android 5.0 is expected in the second quarter of 2012.

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Note to the student. Article selection

▪ article In the struggle you will find your right. Popular expression

▪ article What sign instead of a plus do students in Israeli schools use? Detailed answer

▪ Article Assistant TV Director. Job description

▪ article Compact welding rectifiers. Encyclopedia of radio electronics and electrical engineering

▪ article Two-channel combination lock. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024