LED as an indicator of mains voltage. Scheme, description

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

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Encyclopedia of radio electronics and electrical engineering / Miscellaneous electrical devices

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To indicate the presence of mains voltage in amateur radio designs, neon bulbs are usually used, which do not fit well into the modern design of the front panels of household, measuring and other electronic equipment. A good modern mains voltage indicator can be made on an LED. A diagram of one of the variants of such an indicator is shown in fig. 7.13.

LED as mains voltage indicator

The forward current through LED V1 is limited by resistor R1 and (mostly) capacitor C1. The use of a capacitor for these purposes makes it possible to avoid the deterioration of the thermal regime of the equipment due to the release of a significant amount of heat by the current-limiting resistor. With a negative half-wave of the mains voltage (on the top mains wire according to the diagram), the zener diode V2 works like an ordinary diode, protecting the LED from breakdown by reverse bias.

With a positive half-wave of the mains voltage, the main current flows through the LED V1, since the zener diode is closed. Its voltage stabilization property is used only when the device is connected to the network - by fixing the voltage on the R1, V1 chain, it thereby limits the current surge through the V1 LED and avoids LED failure. The stabilization voltage of this zener diode should be slightly higher than the forward voltage drop of the LED being used. Specific, the value of the capacitance of the capacitor C1 depends on the required forward current through the LED V1.

Author: Semyan A.P.

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Comments on the article:

bear48
The zener diode in this circuit is optional, instead of it you need to put any low-power diode in reverse polarity - the LED "does not like" reverse voltage. Any 1-10 kΩ resistor. The current through the LED sets the capacitor, the main thing is not to exceed its maximum value for a long "life" of the LED.

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