Stabilizer overload alarm

Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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In the article by A. Butov “Audible short circuit alarm” in “Radio”, 2001, No. 10, p. 58 talked about a device that notifies with an audible signal that the voltage stabilizer, made on the KR142EN12A microcircuit, is overloaded, or that there is a short circuit in its output circuits.

Using this idea, I assembled my own version of a similar design (Fig. 1), supplemented with light signaling and having a large range of controlled voltages.

The signaling device itself consists of elements of the DD1 microcircuit and a cascade on the VT2 transistor. A voltage stabilizer is assembled on transistor VT1 and microcircuit DA1 to power the microcircuit, and this transistor, diodes VD1, VD2 and resistors R2, R3 constitute a current generator with a wide range of input voltages. At the output of the current generator, a parallel voltage regulator DA1 is installed, which provides a supply voltage to the DD1 microcircuit at a level of 2,5 V, which is quite sufficient for the operation of a CMOS microcircuit of the specified type.

Now about the operation of the device. The current generator receives voltage from the power supply rectifier, and the top terminal of the trimming resistor R1 in the diagram is connected to the output of the voltage stabilizer. During normal operation of the stabilizer, the resistor slider sets the voltage at the input terminals of element DD1.1 above the threshold, which at a given supply voltage should be about 1,5...1,7 V. Then the output of this element will have a low logical level, which will prohibit operation generator made on element DD1.2. At the same time, a high logic level will appear at the output of this element, and a low logic level at the output of DD1.3. As a result, the generator on element DD1.4 will not be able to operate, but transistor VT2 will open and LED HL1 will flash, indicating that the power supply is turned on and is operating normally.

If the load current of the power supply stabilizer exceeds the permissible limit, the voltage at its output will decrease so much that element DD1.1 will “work.” A high logic level that appears at its output will allow the generator to operate on element DD1.2, resistor R5 and capacitor C2. Pulses with a frequency of 1.3...0,5 Hz will be supplied from the output of the generator to the inputs of element DD1. Low pulse levels periodically trigger the second generator - on element DD1.4, resistor R6 and capacitor C3. It produces pulses with a frequency of 1...2 kHz. The BF1 piezo emitter will begin to emit intermittent sound signals, indicating that the stabilizer is operating in emergency mode. At the same time, LED HL1 will flash, since the base of transistor VT2 receives pulses from the “low-frequency” first generator.

When the power supply stabilizer returns to normal operation, the device returns to its original state.

In addition to those indicated in the diagram, it is permissible to use the KR1561TL1, IW4093BN microcircuits in the alarm device, KT502 transistors with letter indices V, G, E, KT814 with indices B-G (VT1), any transistors of the KT361, KT3107 (VT2) series, stabilizer KR142EN19A (DA1) , any diodes of the KD521, KD522 (VD1, VD2) series, any domestic or imported LED (HL1), piezo emitter ZP-2, ZP-22 (VF1).

Most of the alarm components are mounted on a printed circuit board (Fig. 2) made of one-sided foil fiberglass. The board is installed inside the power supply, and the LED and piezo emitter are installed on the front panel of the case. Opposite the piezo emitter, several holes are drilled in the housing to increase the sound volume.

Setting up the design begins with setting the collector current of transistor VT1 indicated on the diagram by selecting resistor R2. By selecting resistors R5, R6, the desired switching frequency of the generators and the sound tone of the piezo emitter are set. By adjusting resistor R1, you can select any alarm threshold within a wide range. This is facilitated by the relatively low supply voltage of the DD1 chip.

Instead of Schmitt triggers, it is permissible to use 2I-NOT elements of the K561LA7 microcircuit as logical elements (Fig. 3).

If the voltage at the output of the power supply stabilizer is higher than the threshold (normal mode), the output of logic element DD1.1 is low, transistor VT2 is closed, LED HL1 is off, the generator on elements DD1.2-DD1.4 does not work.

In emergency mode, the LED will flash and a continuous sound signal will be heard from the piezo emitter. Otherwise, the operation of the modified signaling device does not differ from the previous one. The desired frequency of the generator is set by selecting resistor R5.

The parts of this alarm are mounted on a printed circuit board (Fig. 4) also made of one-sided foil fiberglass.

Author: I.Potachin, Fokino, Bryansk region

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