High voltage alarm. 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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Increasing the voltage in the network (220 V) can lead to failure of electrical devices. Permissible fluctuations of alternating voltage - 220 V ± 10%. But in the evening and at night, especially in summer (heaters are not used), due to a natural decrease in current consumption (everyone goes to bed), the voltage in the network can increase to 245 V. It is possible to ensure the safety of the electrical equipment of the apartment if you constantly monitor the voltage in the network . I propose for these purposes a simple sound signaling device.

When the voltage in the network exceeds the set threshold (230 V), a loud melodic sound signal sounds. According to it, electrical devices that are "afraid" of increased voltage should be turned off. The signaling device is implemented on the KR1436AP1 microcircuit (foreign analogue - KA2410), which was developed for call nodes of telephone sets. Its "stuffing" includes:

• Schmitt trigger (signal shaper);
• two pulse generators with a frequency ratio of 1:25 (parameters are adjusted by external RC elements);
• output amplifier and reference voltage source.

The last node provides power modes and stabilizes the operation of the generators and the output amplifier, so the microcircuit can be powered from an unstabilized power source.

Since the main purpose of this microcircuit is to work in an analog telephone line, a Schmitt trigger (threshold device with hysteresis) is hidden inside it. The threshold for turning on the internal nodes of the microcircuit depends on the external voltage. In the classic version, the trigger voltage ranges from 17 to 21 V, while the holding voltage (threshold at which the internal components of the microcircuit are turned off) is 9,7 ... 12 V. This switching mode of the KR1436AP1 is recommended by the developers. Pin 2 of the chip remains free.

Consider the signaling circuit. An alternating voltage of 220 V is supplied through the limiting resistors R1 and R2 to the rectifier diode bridge VD1 ... VD4. The rectified voltage is smoothed out by capacitor C1 (K50-12, K50-20, K50-35 and similar) and stabilized by the Zener diode VD5. Such a transformerless source provides power to the DA1 chip. The high resistance of the limiting resistors is explained by the low current consumption of the device. It is 2 and 5 mA in rest and sound alarm modes, respectively. For sound signaling, a piezoelectric emitter ZP-18 is used (ZP-3, ZP-25 and similar can be used).

When a voltage less than the threshold voltage is applied to the DA1 microcircuit, the internal stabilizer does not supply power to the remaining components of the microcircuit. When the mains voltage increases above 230 V, a constant voltage of 1 V or more is supplied to pin 1 of DA17. This voltage turns on generators and other components of the microcircuit, as a result of which the BF1 emitter generates an audio signal. A significant increase in the voltage in the network is not dangerous for the device, since a VD5 zener diode is installed at the input of the microcircuit. which turns on when the DC voltage rises above 27 V and limits this voltage, protecting the microcircuit.

The power unit KR1436AP1 has a hysteresis. This means that it is enough for the voltage at the DA1 input to once reach the threshold value for the microcircuit generators to turn on. They turn off when the supply voltage at the input (pin 1) drops to 9,7 ... 10 V. This property of the microcircuit is especially valuable, since it allows you to record even a single voltage surge in the network in order to take appropriate security measures. If the threshold voltage is exceeded in the DA1 chip, two internal generators, implemented on Schmitt triggers, start working. The first is formed by the Schmitt trigger and the C2-R3 chain. the second also consists of a Schmitt trigger and a timing chain C4-R4. Pulses of infra-low frequency (0,5 ... 1 Hz) from the first generator control the operation of the second. The influence of the first generator is that the pulses of the two generators appear alternately at pin 8. Such a mixed signal is two-frequency. This two-frequency signal is fed to the piezoelectric emitter BF1.

To stop the sound, it is necessary to briefly break the power supply circuit of the device by disconnecting it from the mains. When the alarm turns on frequently, this indicates frequent power surges, and appropriate measures should be taken.

Setting the device is reduced to the exact setting of the threshold. It is advisable to do this at night, during an increase in the voltage in the network, or by turning on the signaling device through the LATR. A DC voltmeter is connected to the output of the diode rectifier. Parallel to the mains outlet - AC voltmeter. By selecting R1 or R2, they achieve stable switching on of the microcircuit generators at a network voltage of more than 230 V. It should be borne in mind that when the resistance of one of the limiting resistors decreases, the signaling device becomes more sensitive to an increase in the mains voltage, and vice versa.

Piezoelectric emitters of the ZP type have a characteristic dependence of the radiation power (sound loudness) on the frequency of sound pulses. With the values ​​\u4b\u22bof the elements indicated on the diagram, the volume of the sound will be sufficient to be heard several meters away (in another room). By changing the resistance R47 within 1 ... XNUMX kOhm, it is possible to tune the internal oscillator of the microcircuit to the resonant frequency of the BFXNUMX emitter, while the sound volume increases significantly.

All fixed resistors are of the MLT type. Diodes VD1.. .VD4 - type KD105B. KD243A-KD243G. You can use diode assemblies KTS402A. KTS407A, KTS405A. Capacitors C1, C2 - oxide (K50-35). The remaining capacitors are ceramic (KM or similar).

Since the device uses a transformerless power supply, the common wire of the device cannot be grounded.

Author: A.Kashkarov, St. Petersburg

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