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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Two-channel triac regulator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers In household portable electric stoves and stationary electric stoves, heaters with several coils switched by switches are used to control power. Such heaters and switches often fail. Single-coil heaters are more reliable, but their power is regulated by the same unreliable regulators with a bimetallic plate. To increase the reliability of electric stoves, it is advisable to install single-coil heaters and a triac power controller in them. A regulator of this type for an electric stove with two burners or for two separate stoves is described in this article. Triac and trinistor power controllers, operating on the principle of applying several half-cycles of mains voltage to an inertial load, followed by a pause, have annoying drawbacks: when working with a powerful load, they cause the lighting lamps connected to the same network to flash. This is especially noticeable if several powerful energy consumers are fed through such regulators at the same time. It is possible to reduce the flashing of the lamps by maximizing the switching frequency of the loads and making them turn on as antiphase as possible. The scheme of the proposed power controller is shown in fig. 1. It is powered by a half-wave diode rectifier VD1. VD2. The quenching function is performed by capacitor C1. and the voltage stabilizer is a VD3 zener diode. In series with the VD2 diode, a chain of LEDs is switched on, indicating the operation of the regulator. This inclusion allows you to get a high brightness of their glow with virtually no reduction in the maximum current given by the power node to the load.
Transistors VT1 and VT2 and resistors R2 - R4 form a pulse shaping circuit at the moments when the mains voltage passes through zero. This kind of device is described in L. Tyushkevich's article "Timistor switch" ("Radio", 1994. No. 9. p. 36.37) and in the author's article "Timistor power controllers" ("Radio", 1996. No. 1. p. 44- 46). The resistances of the resistors R2, R3 are chosen in such a way that the duration of these pulses is short, only about 70 μs (Fig. 2, the voltage diagrams are not drawn to scale for clarity). The generated pulses are fed to the input of the element DD1.1. At its output, they have a positive polarity and charge the capacitor C5 almost to the supply voltage. At the end of the pulse, the voltage across the capacitor C5 decreases exponentially. It reaches the threshold of turning off the elements DD1.3 and DD1.4 (AND-NOT) in about 450 μs. After the end of the pulse at the output of the DD1.1 element, the DDI.2 element switches another 50 μs later.
If the second inputs of the elements DD1.3. DDI.4 from the switches SA2.2 and SA3.2 a high logic level voltage is applied, the pulses pass through these elements and are amplified by the current by emitter followers on transistors VT3 and VT4 and then go to the control electrodes of the triacs VS1 and VS2 and open them. The amplitude of the current of the control pulses is more than 100 mA. total duration - more than 500 μs. they start approximately 30...50 µs before the mains voltage passes through zero. Such pulse parameters ensure the inclusion of triacs of the KU208 series without the need for their selection. The triac is turned on at the very beginning of the half-cycle when its current-voltage characteristic is straightened, due to which there is no interference with radio reception. The passage of pulses through the elements DD1.3 and DDI.4 is controlled by a node consisting of a counter-decoder DD2. diodes VD4 - VD19 and switches SA2 and SA3. The counter-decoder DD2 switches at a frequency of 100 Hz with low-level pulse decays sent to it from the output of the DDI.2 element. This happens, as mentioned above, after about 50 μs after the end of the pulses on the control electrodes of the triacs VS1 and VS2. Diodes VD4 - VD19 form multi-stage OR elements and form such sequences of load switching half-cycles at which their switching frequency is maximum and they work, if possible, in different half-cycles of the mains voltage. In the table, the dots indicate the states of the counter DD2 (conditional numbers of half-cycles), in which loads 1 and 2 are turned on, depending on the positions of the switches SA2 and SA3. As a result, the work of the loads is maximally separated in time, which somewhat reduces the losses in the supply wires. The flickering of lamps included in the same lighting network, which is already barely noticeable due to the rather high switching frequency (12.5 Hz or more), has been reduced. LEDs HL1 and HL3 indicate the inclusion of the corresponding loads. If none of the loads is turned on, the HL2 LED is lit, reminding you that the controller is connected to the network. The power regulator uses switches PG2-9-6P2N (SA2 and SA3), any others with similar contact groups and dimensions will do. Chip K561Tl1 is replaceable for KR1561TL1, K561TM2 - for KR1561TM2. Instead of K561IE9, you can use K561IE8, but with such a replacement, output 8 (pin 9) of the new microcircuit should be connected to its input R (pin 15). disconnecting it from pin 8 to provide a conversion factor of 8. All elements of the regulator, except triacs VS1, VS2. output sockets XI. X2 and switch SA1. mounted on a printed circuit board with dimensions of 50x120 mm (Fig. 3). The board is designed to install MLT resistors, capacitor K73 - 16 (C1), an imported analogue of the capacitor K50-35 (C4) and capacitors KM-5 (C2, C3, C5). Diodes VD1. VD2 - any silicon pulse or rectifier, VD3 zener diode - for a stabilization voltage of 13 ... 15 V. Transistors VT1 and VT2 can be any low-power silicon pnp structures. transistors VT3 and VT4 - medium or high power of the same structure with a permissible collector current of 150 mA.
You can use any LEDs, including multi-colored ones. You should pay attention to their installation - they should be maximally (as far as the conclusions allow) taken out of the board and directed in the same direction as the axes of the switches. Triacs KU208G (or KU208V) are mounted on ribbed heat sinks 25x50x60 mm in size. Board, heat sinks with triacs. two pairs of sockets and an SA switch (TV 1-2) are placed in a plastic box with dimensions of 70x95x150 mm. At the same time, the board is located as close as possible to the bottom wall of the box, the heat sinks are to the top (these are 70x150 mm walls). 42 holes with a diameter of 6 mm with a pitch of 10 mm LEDs and switch axles are brought out through the holes in the front wall of the box The axles and fixing screws of plastic switch handles should not be accessible for accidental touch. When using serviceable radio elements and there are no installation errors, the regulator does not require adjustment. If it does not work right away, the following troubleshooting procedure can be recommended. Turn off the triacs and short-circuit the terminals of the resistor R2. Between the positive terminal of the capacitor C4 and the right terminals of the resistors R7 and R8 according to the scheme, turn on any type of LED (plus - to C4). Without disconnecting anything from the DD1.1 element, turn it into a pulse generator with a frequency of approximately 1 Hz. by soldering a 9 kΩ resistor between terminals 10 and 100, and an oxide capacitor with a capacity of 7 μF for a voltage of at least 8 V between terminals 10 and 16 (positive terminal to terminal 8). Close the terminals of the capacitor C1 and through a resistor with a resistance of 510 Ohm (0.25 W) connect to the network inputs of the regulator (Fig. 1) a DC power supply with a voltage of 22 ... . Next, you should make sure that the HL24-HL1 LEDs are turned on correctly with different positions of the switches SA3 and SA2. Using a voltmeter or a logic level indicator, check the presence of pulses at the outputs of the counter DD2 and on the sliders of the switches SA2.2 and SA3.2, as well as the passage of pulses through the elements DD1.3, DDI.4 and emitter followers on transistors VT3 and VT4 on additional LEDs according to the table.
If you have an oscilloscope, it is better to set the generator frequency to approximately 1000 Hz by soldering a capacitor with a capacity of not 1.1, but 10 uF to the DD0,01 element, but additional LEDs in this case must be connected in series with 2.2 kOhm resistors. If, after such a check and restoration of the device circuit, it still does not work, then either the pulse formation circuit VT1, VT2, R2, R3, or the triacs are faulty. Author: S. Biryukov, Moscow
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