Fuse against overvoltage in the network. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Fuse against overvoltage in the network. Encyclopedia of radio electronics and electrical engineering

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

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Unfortunately, in many settlements, the voltage in the electrical network can fluctuate widely enough to disable the equipment with the next increase.

This describes an electronic fuse circuit that disconnects the load from the mains when the mains voltage exceeds a certain certain level. The load is connected to the network only after one minute, after the voltage in the network is restored. A minute delay is needed so that there is no intermittent or impulse connection of the load in the case when there are frequent fluctuations in the network, accompanied by voltage surges.

The circuit is shown in the figure.

(click to enlarge)

The mains voltage value sensor is a circuit based on two zener diodes VD2-VD3 and resistors R1-R2-R3. Also, the threshold value of the logic level of the D1 microcircuit plays a role. This circuit receives positive half-waves from the network through the VD7 diode. Resistor R2 is adjusted like this. so that when the mains voltage is within acceptable limits, the zener diodes VD2 and VD3 are closed, since the voltage on them is less than their total stabilization voltage. But when the voltage rises above the permissible limit, these zener diodes open, since the voltage on them in this case should be greater than their total stabilization voltage.

Thus, at normal voltage in the network at pin 12 D1, a logical zero, and at an increased voltage - one. The VD8 zener diode protects the meter input from increasing the voltage on it above the meter supply voltage (for this microcircuit, this is fatal). Capacitor C2 with resistor R4 forms a low-pass filter that suppresses interference and short pulses, for example, from the operation of a power tool.

The counter D1 has a timer of one minute.

This is the CD4060B counter, it is already widely known to radio amateurs. Let me remind you that it has a binary counter and inverters for building a multivibrator circuit. Details R6-R7-C3 just work in this multivibrator. Diode VD4 is set to automatically block the multivibrator when the counter goes to "8192". This diode is connected to the input of the first multivibrator inverter.

After switching on, under the condition of normal mains voltage, the counter D1 immediately starts working, and after a minute it is in the "8192" position. Its pin 3 is set to one. The key on transistors VT1 and VT2 opens and the load is connected to the network. Diode VD4 opens and blocks the multivibrator. The circuit stops in this state.

If the voltage in the network rises above the permissible value, then a unit voltage appears at pin 12 D1. The counter is reset. At its output 3 - zero, transistors VT1 and VT2 are closed, the load is turned off. As long as the voltage is consistently above the allowable voltage at pin 12, D1 is one, and D1 is fixed in the zero state.

After the voltage drops to a safe value, the counter starts and after a minute its output 3 will be one. Keys VT1 and VT2 open and connect the load. If during this minute there was again a power surge, then the counter is reset, and the countdown of the minute delay starts again. Thus, the load is connected only after the voltage in the network has been established within acceptable limits and all transient processes, for example, associated with an accident at the station, have ended. The logic circuit is powered from the mains through a rectifier on VD7 and a parametric stabilizer R6-VD1. Diodes VD6, VD7, together with resistor R8, prevent counter failures due to too high capacitance of the gates of the key transistors (charging these capacitances creates a current pulse that overloads the counter output, because of this, the counter can be reset or set to an arbitrary state). With a load power of up to 400W, no radiators are required for VT1 and VT2. The maximum load power is 1000W, but this is already with radiators.

Almost everything is assembled on a printed circuit board with single-sided tracks. Zener diodes KS551A can be replaced by others. It is important that the total stabilization voltage of these zener diodes be about 90 ... 110 V. For example, instead of two KS551A, you can put three KS533A or one KS591A. Zener diodes D814D can be replaced by others for 10 ... 15 V, for example, KS213B, KS512A. or imported. In place of VD1, it is desirable to use a D814D zener diode in a metal case or KS512A, since significant power is dissipated on it.

In place of VD8, you can use any zener diode, but for the same voltage as VD1. Diode KD105B can be replaced by KD105, KD105G KD127A, KD209, KD236, KD243G, KD243E KD243ZH KD247V, KD247G, KD247D, KD247E, KD248, KD258V, KD258G KD258D, KD281D, KD281E, KD281J, KD281I, KD281K KD281L, KD281M, 1N4004, 1N4005, 1N4006, 1N4007, 1N5404, 1N5405, 1 N5406, 1 N5407, 1N5408. Diodes KD521A can be replaced with KD521B, KD522 KD503 KD510. 1N4148. Resistors R1 and R6 must be at least 0,5 watts.

Mains overvoltage fuse

Trimmer resistor R2 type SPZ-19.

Capacitors C1 and C2 must be at least 12 V. Set the fuse to the maximum allowable voltage with resistor R2, applying voltage to it from LATR. It is necessary to connect an oscilloscope or a logic probe to pin 9 D1, which can show the presence of pulses. Diode VD4 temporarily unsolder. First, the normal voltage is set and by adjusting R2, they achieve that there are pulses at pin 9 D1. Then, the voltage is set at the upper limit, for example, 250 V, and by adjusting R2, they achieve such a position that the pulses disappear at the voltage threshold of 250 V, and if less, they appear again.

Then, after turning off the power, solder VD4 in place, connect a load (for example, a light bulb) and check the operation of the circuit. The lamp will not turn on immediately after power is applied. After the bulb has turned on, first set the normal voltage (220 V), then increase it. At the threshold value (250 V), the lamp should go out.

Author: Savichev D.A.

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