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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Economic photorelay. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting Radio amateurs pay great attention to the issues of saving electricity - this is evidenced by numerous publications in the magazine "Radio" with a description of photorelay - devices for turning off lighting during daylight hours. The proposed photorelay (its circuit is shown in the figure) has a low own power consumption and is connected via a two-wire circuit in parallel with the standard switch. The device contains a powerful electronic key on the triac VS1, connected in parallel to the standard switch SA1. The operation of the triac is controlled by a low-current switch on a composite transistor VT2VTZ included in the diagonal of the diode bridge VD4-VD7. Resistor R5 in the emitter circuit of the transistor VT2 prevents the operation of the transistor VT3 in the "broken" base mode when the transistor VT2 is closed. The low-current switch is turned on by the base current of the transistor VT2 flowing through the resistor R4. As you know, the current transfer coefficient of the base of a composite transistor is equal to the product of the transfer coefficients of the transistors that make it up. For the transistors used by the author, the minimum value of this coefficient is 30, i.e., the current transfer coefficient of the base of the composite transistor in this case is not less than 900, which makes it possible to use a sufficiently high-resistance resistor R4, while the power consumed by the device will not exceed 0,15 W in standby mode , and after the operation of the photorelay - much less.
The light-sensitive element is a VD1 photodiode, which is used as an infrared photodiode FD256, which has sufficient sensitivity in the visible region of the spectrum. On the Schmitt trigger DD1.1 made a threshold element. The response threshold is regulated by a tuning resistor R1, the capacitor C1 increases the noise immunity of the device. On element DD1.2, resistor R2 and capacitor C1.3, a relay switching delay unit is made, which eliminates false positives during short-term illumination of the photodiode, on element DD1 - an inverter to provide the necessary operation logic, on transistor VT1 - output switch. The DD3 chip is powered by a parametric voltage regulator on the VD4 zener diode and the R2 resistor. Diode VDXNUMX prevents the discharge of the filter capacitor C3 when the photo relay is activated. The Schmitt triggers of the DD1 microcircuit are included by inverters, and, at first glance, they can be replaced by inverters from the elements 2I-NOT or 2OR-NOT of the K561LA7 or K561LE5 microcircuit. However, in this device, such a replacement is incorrect. The voltage at the inputs of the elements DD1.1 and DD1.2 changes slowly: for the first one, due to a smooth change in the level of natural light, and for the second one, due to the large time constant of the RЗС2 circuit. Schmitt triggers have a clear response threshold, and the logic elements in this place of the input characteristic have an uncertainty zone when one of the input transistors has not yet had time to close, and the second has already begun to open. As a result, there is a through current through the transistors and the current consumed by the microcircuit increases sharply. The input circuit of the key on transistors VT2 and U1Z operates in microcurrent mode, and such a change in the operating mode of the microcircuit will lead to malfunctions in the device. The proposed photorelay works as follows. When it is connected to the lighting network in parallel with the standard SA1 switch, capacitor C4 will be charged for several half-cycles of the current rectified by the VD7-VD3 diode bridge. When the voltage on it reaches the breakdown voltage of the zener diode VDZ (in microcurrent mode it is less than the stabilization voltage, normalized at a current of several milliamps), transistors VT2 and U1Z will open. When the current through the transistors reaches a value sufficient to open the VS1 triac, it will open, shunting both the switch and the VD4-VD7 diode bridge. Capacitor C3 will be recharged at the beginning of each half-cycle of mains voltage, while triac VS1 is closed. When the device is connected, the capacitor C2 is discharged, the voltage at the inputs of the DD1.2 element is 0, the voltage at its output is log. 1, and at the output of the element DD1.3 - log 0, so the field-effect transistor VT1 is closed and does not have any effect on the operation of the device. Further operation of the device is determined by the level of illumination of the photodiode VD1. If it (level) is insufficient, then the reverse resistance of the photodiode is high, there is a log level at the inputs of the DD1.1 element. 1, at the output - log level. 0, and no changes in the operation of the device occur - at the beginning of each half-cycle of the mains voltage, the triac VS1 opens, supplying voltage to the lighting lamp EL1. As the light level increases, the reverse resistance of the VD1 photodiode decreases, and at some point the voltage across it becomes less than the Schmitt trigger threshold DD1.1 - a log 3 level appears at its output (pin 1), while the current through the resistor R2 starts charging capacitor C2. After a few tens of seconds (depending on the capacitance of the capacitor C3 and the resistance of the resistor R1.2), the voltage at the combined inputs of the Schmitt trigger DD4 reaches the trigger level, and a log 0 level appears at its output (pin 1.3). As a result, the DD10 element switches to its output (pin 1) appears log level 1 and the field-effect transistor VT2 opens, shunting the emitter junctions of transistors VT3 and VT1. In the future, the transistor VT1 remains open, and a current flows through the control electrode of the triac VS4, limited by resistor R1 to a maximum amplitude of less than XNUMX mA, which is less than the opening current of the triac. During experiments on replacing the TC106-10-10 triac with imported triacs, it turned out that for some instances of the VT137-600 triacs, the opening current is less than 1 mA, and the triac, when the photorelay is in standby mode, opens when the maximum amplitude of the mains voltage is reached, while the EL1 lamp shines half-heartedly. For normal operation of a photorelay with such a sensitive si-mistor, the resistance of the resistor R4 had to be increased to 1 MΩ. When the illumination level decreases, the reverse resistance of the photodiode VD1 increases, the voltage at the inputs of the DD1.1 element rises and at some point the Schmitt trigger DD1.1 switches - a log level appears at its output. 0. Capacitor C2, charged to the supply voltage, begins to discharge through resistor R3. After a few tens of seconds, the voltage at the inputs of the DD1.2 element decreases so much that the DD1.2 element, followed by DD1.3, switches, a log level appears at the gate of the transistor VT1. 0, and it closes, ceasing to shunt the emitter junctions of the composite transistor UT2UTZ. At the beginning of each half-cycle, it opens and turns on the triac VS1 - while the EL1 lamp shines. With short-term illumination of the photodiode VD1 (for example, by the headlights of a passing car, lightning flashes, etc.), the voltage on a completely discharged capacitor C2 does not have time to change significantly - this achieves a high noise immunity of the proposed photorelay. About details. Transistors MJE13002 and diodes 1N4007 removed from the electronic ballast of a faulty CFL. Criteria for replacing transistors: collector-emitter voltage - not less than 400 V, maximum collector current - not less than 100 mA, static current transfer coefficient of the base h21Э - more than 25. If this transistor parameter is less than 25, then the resistance of the resistor R4 should be reduced to 200 kOhm. Requirements for VD4-VD7 diodes - direct current of at least 100 mA, reverse voltage of at least 700 V. Triac TS106-10 must be at least class 5 in voltage, i.e. withstand a voltage of at least 500 V in the closed state. When replacing the triac indicated in the diagram with an imported one, it is necessary to take into account the switched power and bear in mind that the current through the cold filament of a lighting lamp is 5 ... 10 times higher than the nominal one. With a load power of more than 200 W, the triac must be installed on a heat sink. The FD256 photodiode was removed from the SDU of an old TV. Photodiodes in the visible part of the spectrum are very rarely on sale, so in the absence of FD256, it is worth experimenting with other types of IR photodiodes. The criterion of suitability is not less than a tenfold change in the reverse resistance with a change in illumination. Some IR photodiodes, which were previously used in industrial equipment, have good sensitivity in the visible part of the spectrum. Very good, for example, are IR photodiodes extracted from smoke fire detectors, for example, of the IP-212 type, which are thrown away in large quantities during the repair of fire alarms that have reached their established service life in institutions and organizations. It is necessary to illuminate the photodiode during experiments with an LED lamp that has minimal radiation in the infrared region of the spectrum. Zener diode VD3 - any low-power with a stabilization voltage of 3,3 ... 5 V, diode VD2 - any low-power silicon. We will replace the KP501A transistor with any of the KP501, KP504, KP505 series. Possible replacement of the KR1561TL1 chip - K561TL1, 564TL1 or an imported analogue of CD4093B. Fixed resistors - any type of dissipation power indicated on the diagram (the dissipation power of the resistor R4 - 0,5 W - was chosen for reasons of electrical strength). Trimmer resistor R1 when installing the device indoors - any type, when located outdoors, it is desirable to use a resistor of a closed design, for example, SPO-0,15, SPO-0,5 or SP4-1. To seal the internal cavity of the resistor, a layer of technical vaseline or CIATIM grease should be applied to the engine roller at the point where it exits the housing. Capacitors C1, C3 can be of any type, both film and ceramic, C2 - imported oxide (nominal voltage - 50 V - chosen significantly higher than the working voltage for reasons of good interlayer insulation - the higher the rated voltage, the better the insulation, i.e. less leakage current). The device is assembled on a fragment of a universal breadboard with dimensions of 45x25 mm. When using serviceable parts and there are no errors in the installation, the adjustment comes down to setting the desired threshold with the trimming resistor R1. To protect against atmospheric influences, the adjusted board is covered with nitro-lacquer in two layers and placed in a housing from the IP-212 fire detector, which has a good appearance. Author: K. Moroz
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