Light and sound signaling device of failures of mains voltage. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network

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In many regions of our country, the quality of electricity supply today leaves much to be desired. The voltage in the household AC network not only "floats" from 160 to 260 V, but also has frequent short bursts and dips, leading to malfunctions of electrical appliances. By introducing voltage stabilizers into the equipment, it is made insensitive to slow changes in its value.

Voltage surges are more or less successfully dealt with with the help of filters and varistors. But a failure in the operation of an electronic device caused by a short-term decrease in the supply voltage often seems inexplicable, since it is very difficult to notice such a decrease “by eye”. The author proposes to make a signaling device that notifies about it. This will remove suspicions of a malfunction from an unexpectedly turned off or turned on household appliance and direct efforts to eliminate the cause of the incident in the right direction.

The device is designed to signal a short-term significant voltage drop in the 220 V network, which is not always noticeable by the flickering of incandescent lamps. This simple design signals a possible cause of an unexpected restart of the computer, a failure of the microwave oven program, a washing machine, and a sudden shutdown of the TV. It should be noted that with such "failures" of the mains voltage, some personal computers, televisions and other devices that are not completely disconnected from the network, but are in standby mode, can spontaneously switch to the operating mode. The logic of the device, the scheme of which is shown in Fig. 1 is very simple.

Rice. 1 (click to enlarge)

When the supply voltage is applied, capacitors C2 and C4 are quickly charged. Capacitor C6 of the rectifier filter that feeds the DD1 chip charges much more slowly - up to a voltage of 9 V for about 30 s. Due to this, at the beginning of the operation of the device at the output of the element DD1.1, the voltage level will be low. Since the capacitor C5 is discharged, the Schmitt trigger on the elements DD1.2-DD1.4 will be in a low state at the outputs of the elements DD1.3 and DD1.4. The HL1 LED is not lit, the buzzer with the built-in generator HA1 does not work. With a significant decrease in the voltage in the network for a duration of more than 60 ms, the capacitors C2 and C4 will be discharged, which will lead to a change in the low level at the output of the element DD1.1 high.

Capacitor C4 will be charged through the opened diode VD5. This will change the state of the Schmitt trigger. The LED HL1 and the buzzer HA1 will be turned on. At the end of the "failure", the light and sound signals will not stop, since the capacitor C5 will remain charged. The discharge of this capacitor occurs through the resistor R7. With the values ​​\u5b\u7bof C1 and R1 indicated in the diagram, the signals are given for approximately a second. The L1C3R8,5 filter prevents false activation of the signaling device under the influence of interference. The Zener diode VD9,5 limits the supply voltage of the microcircuit to XNUMX ... XNUMX V.

Instead of the K561LA7 chip, you can use the K561LE5 or similar chips of other domestic and imported CMOS series. However, it is not recommended to use K176 series microcircuits that do not have protective diodes. If the input voltage exceeds the supply voltage, they can fail as a result of the "thyristor effect". Instead of the D814B1 zener diode, you can install another low-power one with a stabilization voltage of 8 ... 9,5 V. KD521A diodes are replaced by any of the KD521, KD503, KD510, KD522 or 1N4148 series, and KD243Zh - from the KD243, KD209 or 1N4003 - 1N4007 series. Capacitor C1 - high-voltage ceramic, for example K15-5. With some decrease in reliability, a film capacitor for an operating voltage of 630 V can be used here. Capacitor C2 should also be film. Oxide capacitors - K50-35, K50-68 or their imported analogues.

Resistor R1 is desirable to use a "non-flammable" R1-7 or imported. The remaining resistors of general use of the corresponding power. LED HL1 - any of the series KIPD21, KIPD40, L-1503, L-1513, preferably red or orange glow. The HPA24AX sound emitter can be replaced by another one with a built-in generator and a current consumption of not more than 15 mA, for example, EFM-250, EFM-472A, TFM-02D. All parts of the signaling device, except for the LED and the sound emitter, are mounted on a printed circuit board, shown in fig. 2.

The finished device is housed in a spacious housing of the "Sven Platinum" surge protector. The author strongly discourages the purchase of now widespread extension cords with housings and, moreover, socket bases made of flammable thermoplastic plastic, such as polystyrene. If desired, by selecting capacitors C2 and C4, you can change the sensitivity of the device. It is more convenient to select capacitor C4, reducing its capacitance until the increase in voltage ripple at the inputs of element DD1.1 leads to an alarm. After that, it is necessary to install a capacitor C4 with a capacity of 20 ... 30% more than that found. A correctly configured signaling device should give a signal when a load of 1 ... 4 kW is connected to the same socket (for example, a photo-illuminating halogen lamp).

Author: A.L. Butov, p. Kurba, Yaroslavl region; Publication: cxem.net

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