Mains voltage LED indicator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Mains voltage LED indicator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Indicators, sensors, detectors

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Often in everyday life there is a need to control the mains voltage. In the recent past, neon bulbs with quenching resistance were used for this purpose. Later, LEDs with a quenching resistance or a capacitor began to be used. Since the LED consumes much more current than the neon indicator, the power of the quenching resistance has increased. And if a flashing indication is necessary to attract attention? In this case, you can use a blinking LED, for example, from Kingbright, but it consumes significant current, and its price is an order of magnitude higher than a conventional LED. You can assemble the circuit yourself to your liking with a minimum current consumption.

I offer the attention of readers just such a scheme (see figure). The circuit is powered by a transformerless circuit using a quenching capacitor C3. Resistor R1 limits the charging current of the capacitor through the diode-zener diode bridge VD3 ... VD6 at the time the device is connected to the network.

Mains voltage LED indicator

This bridge serves as both a rectifier and a stabilizer to power the circuit. Capacitor C2 smoothing and storage. The flasher itself, as can be seen from the diagram, is assembled on three transistors VT1 ... VT3, diodes VD1, VD2, capacitor C1 and a light emitting diode HL1. The scheme is based on the publication [1].

When the supply voltage is applied to the circuit, all transistors are closed, the charging of the capacitor C1 begins through the circuit VD1, R3, HL1, R6. When the voltage at the emitter of transistor VT1 becomes less than at the base, it opens. The collector current of this transistor opens the composite transistor VT2, VT3. Capacitor C1 starts to discharge through VT1, R4, VT2. In addition to this circuit, the capacitor is also discharged along the circuit: VD2, R5, VT3. A powerful pulse of the collector current of the transistor VT3, limited by the resistor R6, leads to a bright flash of the HL1 LED. The flash period is determined by the capacitance of the capacitor C1 and the resistance of the resistor R3, and at the values \u1b\u0,6bspecified in the diagram, it is approximately 10 s. The average current consumption is XNUMX mA, so it became possible to limit the capacity of the quenching capacitor to only XNUMX nF.

The proposed scheme can be used in everyday life for various applications: from an indicator built into a switch that can be found in the dark, to an imitator of a guarded object.

You can use a garland of LEDs for flashing, in this case you need to turn on several LEDs, replace the zener diodes with higher voltage ones and, accordingly, increase the operating voltage of the electrolytic capacitors used.

The circuit used resistors of the MLT type, electrolytic capacitors of the K53-14 type, any silicon diodes. Capacitor C3 type K73-17. Transistors VT1, VT2 any silicon corresponding conductivity. As VT3, transistors of the types KT3117, KT503, KT603, KT630 can be used. The scheme requires almost no settings. By selecting resistor R6, the required brightness of the LED glow is set, resistor R3 is the repetition period, and resistor R5 is the duration of the LED flash. These two parameters are also affected by the capacitance of the capacitor C1.

References:

Adjustable pulse generator//Radio. -1990. - No. 8.

Author: O. V. Belousov

See other articles Section Indicators, sensors, detectors.

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