Network indicator of inclusion on a two-color light-emitting diode. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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The proposed simple device, assembled from available parts according to the diagram in Fig. 1 is designed for operation in 220 V AC circuit. It allows displaying three different states: 1 - when the device cord is plugged into a 220 V socket, but the device is turned off - the two-crystal LED shines with a weak red color; 2 - when the device is turned on (contacts SA1 are closed), i.e. the device is working, the LED glows green; 3 - when the protective fuse FU1 blows in the power supply circuit of the device - the HL1 LED shines bright red.

The connected load can be of any type, for example, a power adapter, a charger, an electric stove, a vacuum cleaner, a laboratory power supply. The device can be built into structures that do not have their own display elements, or to upgrade their old display units, made according to very simple schemes.

Let's analyze the first situation - when the power cord is inserted into the socket, but the device is turned off (SA1 contacts are open). Weak, not tiring vision, but a noticeable reddish glow of the LED will remind you in time that the device is supplied with power - when you touch live parts, you can feel dangerous 220 V mains. The alarm will prevent interference with the structure without disconnecting it completely from the network . Many major industrial manufacturers of household appliances recommend that during long breaks in the operation of their products, still unplug the power cord from the outlet, and not rely only on the built-in mains switch. This is especially true during thunderstorms.

When operating in the above mode, the LED receives power through the R1, VD1 circuit, the power consumed by the indicator (most of which is dissipated by the resistor R1) will be about 70 mW.

When the SA1 contacts are closed, the device is supplied with an AC supply voltage of 220 V. Through the VD3, R6 circuit, the "green" crystal HL1 is powered, the transistor VT2 opens, which shunts the "red" crystal HL1 - the LED shines quite bright green. The power consumed by the display unit from the network does not exceed 0,6 W (to the heat dissipated by R1, the thermal energy dissipated by the current-limiting resistor R6 is added). When the SA1 contacts are closed, the LED will glow green even when the load is off.

In the event of an emergency blown fuse FU1, a high-voltage p-n-p transistor VT1 opens. LED HL1 lights up bright red. If at the same time the load is not connected, then a weak illumination of the "green" crystal HL1 will be noticeable. The dissipated power on R2 at a supply voltage of 220 V will not exceed 0,7 W.

In the event of an accident in the power supply network, the input supply voltage is about 380 V (in fact, FU1 must burn out at the same time), the power dissipated by R2 will not exceed 2 W, which, although it will lead to its strong heating, is not capable of causing it to ignite. Taking into account the possible round-the-clock operation of this node, it was decided to abandon the use of film capacitors that quench excess current, which should have been highly reliable and with a large voltage margin. The use of current-limiting resistors with a large margin of power is more reliable, given that in normal mode this device consumes no more than 0,6 W of power from the network.

In a device assembled in accordance with the diagram in Fig. 1, you can use fixed resistors C1-4, C2-23, C2-33, MLT of the appropriate power. In place of R2, R6, it is advisable to use non-flammable domestic resistors of the P1-7 type (the case is painted with gray paint) or special imported discontinuous ones. It is desirable to install the same resistors at a height of 15.. .20 mm from the base of the printed circuit board. Rectifier diodes can be any silicon ones that allow a reverse voltage of at least 600 V, for example, KD243D, E, Zh, KD247P D, KD105V, G, 1N4006, RL106.

The cheap and common high-voltage transistor VT1 can be replaced with KT9178A, KT851B, KT505A, MPSA-92, BF493, 2SA1625 M, L, K. The VT2 transistor is replaced by any of the KT3102, KT312, KT645, KT503, SS9014, 2SC2001, 2SC900 series. Considering the small currents flowing through the HL1 crystals, it is desirable to take the LED with increased light output. The author used an imported double-crystal LED from Kingbright in a transparent case 5 mm in diameter. Its brightness is 150 mCd for both "red" (GaAsH/GaP) and "green" (GaP) crystals.

Instead, you can use similar dual-anode LEDs, for example, L59SRCG / CC, L59SURK-MGKW, L59EGW, L799SURKMGKW, L119SRGWT / CC, L93WEGC. The mentioned LEDs have good luminosity, but the design and type of LED housings of different series is different.

On the printed circuit board of this device, there is a place for installing a fuse FU1. If the finalized design has "its own" similar fuse, then the terminals of its clip should be connected to the printed circuit board with two flexible wires of sufficient cross section. If the standard switch of the device, indicated on the diagram as SA1, is dual (as most often happens), then the second group of its contacts should be included in the circuit "to the right" of point "A", which does not present any difficulties.

The device can be mounted on a printed circuit board (Fig. 2) made of one-sided foil fiberglass with dimensions of 70x40 mm. The LED can be installed both on the printed circuit board itself and in any convenient place of the product, for example, instead of the usual single-color LED, which served as an indicator earlier.

A properly assembled device does not require adjustment. When checking its performance, it should be taken into account that it is galvanically connected to the 220 V AC mains, and appropriate precautions should be taken. However, just the glow of HL1 will remind you in time that before soldering or unscrewing something, you should unplug the power cord from the outlet. When the current consumed by the load is more than 3 A, the printed power tracks should be "reinforced" with a copper stranded wire with a diameter of at least 1 mm.

Author: A.Butov, village of Kurba, Yaroslavl region

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