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Power failure indicator

Power failure indicator

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What is it for?
Do not be misled by the title of this flash editing that could make believe a joke of April 1st. Indeed, simply plug in any lamp into a wall outlet to realize a power cut.
Our assembly has a different function in that it knows how to keep the visual trace of any interruption, even of very short duration, of the sector.
The utility of such a device is no longer to be demonstrated in many fields: microcomputer, of course, where the disappearance of the sector can have unfortunate consequences on systems that are not powered by an inverter, but also In everyday life, where the cutting of this same sector for a sufficient time can damage the contents of a freezer for example.

The schema
Numerous solutions can be envisaged to achieve this result, the simplest ones using a CMOS circuit powered by batteries. Although these components are very energy-efficient, which gives a long life to the batteries, we find it a shame not to take advantage of the energy that we provide precisely this sector that we want to monitor. To do this, and as you can see, our assembly is powered directly by the latter.
The use of a CMOS circuit and LEDs whose power supply has been deliberately reduced makes it possible to overcome the conventional but bulky power supply transformer and to use a simple capacitor as a voltage reducing element. The power dissipated in the latter is practically nil but, on the other hand, it is hardly to expect to be able to consume more than 10 mA on such a power supply. That's enough here.
The core of the assembly is a simple R-S flip-flop made up of two Schmitt trigger CMOS gates. Taking into account the respective values ​​of the capacitors C3 and C4, the assembly always starts with the flip-flop in the same state, which corresponds to the illumination of the red LED. The principle of indicating the disappearance of the sector is entirely based on this finding. In fact, when the circuit is switched on, the red LED lights up. Pressing the pushbutton changes the state rocker. The red LED goes off and the green LED lights up. This situation is prolonged as long as the sector remains present. As soon as it disappears or, more precisely as soon as it returns, the assembly starts with the red LED on, signaling the occurrence of at least one disappearance, which is indeed the aim. Given this principle, it is obvious that the extinction of both LEDs signals an area absent at the present moment.

The assembly does not present any difficulty, all the components taking place on the small printed circuit that we have drawn, the only precaution to be taken concerns C1 which must imperatively be a capacitor of class X or X2 intended to operate directly on the sector 220 V alternative . Do not use a 400 V operating voltage capacitor, even if some dealers claim it is possible; It is the safety of your assembly. If you can not find an X or X2 capacitor, use a 630 V operating voltage model. The operation of the assembly is immediate and poses no problem. Do not forget, however, that it is connected directly to the mains and that it must never be put in the hands when it is connected. A casing and especially an insulating push-button are essential to ensure your safety.

Nomenclature of components

IC: 4093 CMOS-T1, T2: BC547, BC548, BC549
D1, D2: 1N4007 - D: 1N914, 1N4l4B - DZ1: Zener 9.1 V 0.4 W BZY88C9V1
LED1: red LED - LED2: green LED

Resistors 1/2 or 1/4 W 5%
R1: 1kR 1 / 2W
R2, R3: 22 kR
R4, R5:
R6, R7: 1 KR

C1: 0.22 uF class X or X2 for 220 V sector
C2: 10 uF 25 V chemical radial
C3: 1 uF 25 V chemical radial.
C4: 0.1 μF mylar

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