Emergency shutdown device. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network, uninterruptible power supplies
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The proposed device (its diagram is shown in Fig. 1) will disconnect the load from the network if its voltage exceeds a predetermined threshold value, and automatically connect it again when it becomes less than the threshold value.
Fig. 1
The basis of the device is two relaxation RC oscillators on dinistors: the first one is on VS1 and the elements R2, R3, C2, the second one is on VS2 and R7, C4. They form pulses at the moments when, during the charging process, the voltage on the capacitor C2 (in the first generator) and C4 (in the second) reaches a value equal to the opening voltage of the corresponding dinistor (more on the operation of such a generator can be found in the article "From the details of energy-saving fluorescent lamps" , published in "Radio", 2012, No. 6, p. 26).
The generators are powered by a diode rectifier VD1 with a smoothing capacitor C1. Resistor R1 limits the inrush of the charging current of this capacitor when the device is connected to the network. If its voltage is below the threshold value, the first generator (on the VS1 dinistor) is inhibited, and the second one (on VS2) works and its pulses open the VS3 triac. Since the frequency of their repetition is quite large (several hundred hertz), the triac opens at the beginning of each half-cycle of the mains voltage. The protected load is connected in series with the triac, so almost all the mains voltage is supplied to it.
When the network voltage exceeds the set threshold, the first generator starts to work. Its pulses through the diode VD2 charge the capacitor C3, and the transistor VT1 opens. As a result, the voltage on the capacitor C4 decreases to the saturation voltage of the collector-emitter of the transistor (fractions of a volt), the second generator stops working and the closed triac VS3 disconnects the load from the network. When the mains voltage becomes less than the threshold, the device returns to its original state - the mains voltage is again supplied to the load. The operating threshold of the device is set by a trimming resistor R3.
Fig. 2
The PCB drawing is shown in fig. 2, and the appearance of the device mounted on it is shown in Fig. 3. Fixed resistors - MYAT, P1-4. C2-23, trimmer - SPZ-19a, capacitors C1 and C3 - imported oxide, C2 and C4 - MSC film series or ceramic K10-17 (their capacitance can be in the range of 0,015-0,033 microfarads). Dinistors DB3, diodes 1N4007, transistor PN2907A and capacitors C1, C2, C4 of the ratings indicated in the diagram can be taken from failed energy-saving CFLs (compact fluorescent lamps), of course, provided that these elements are working. ConnectorX1 - screw terminal block X977B04 (DG25C-B-04P), it can be replaced by any other similar one, capable of operating at a voltage of 300 V and a current through the contacts not less than the load current. The assembled board is placed in a housing made of insulating material and fixed in it with hot glue.
Fig. 3
With a trinistor without a heat sink, the device can be used to protect loads up to 200 W. With an appropriate heat sink, it can reach 2 kW. The triac TS106-10-8 will be replaced by others of this series or imported series VT138, VT139, MAC15 with a permissible voltage of at least 600 V. During operation, it should be remembered that the current consumed by the load must be greater than the holding current of the triac, otherwise the device will work will be unstable.
Author: I. Alexandrov
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