The switch of three garlands on two-color light-emitting diodes. Scheme, description

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The switch of three garlands on two-color light-emitting diodes. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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The use of two-color LEDs in the garland switch allows you to get the effect of periodically changing the color of individual LEDs while maintaining the overall brightness of the garland.

On fig. 3 shows a diagram of a switch of three garlands for two-color LEDs with an anti-parallel connection of emitting crystals (the parameters of the LEDs are published in the Reference Sheet in Radio, 1998, No. 11. p. 57; 1999, No. 1. p. 51). It has three generators of rectangular pulses on the logic elements of the DD1 chip, three switches on transistors VT1 - VT6 and a power supply. From the secondary winding of the transformer T1, an alternating voltage is supplied through the quenching resistors R7-R9 to three garlands assembled from series-connected LEDs.

Switch of three garlands on two-color LEDs

At the same time, the alternating voltage is rectified by the VD8 diode. The rectified voltage is smoothed by capacitor C8 and fed to the parametric stabilizer R10VD7. from which the generators are powered. The stabilized voltage is additionally smoothed by capacitor C7.

Each generator is assembled according to a well-known scheme on two inverters with frequency-setting RC chains with their own ratings of parts. Therefore, the pulses at the outputs of the generators follow with different frequencies.

The switch that controls the first garland on LEDs HL1-HL10 is assembled on transistors VT1, VT2. A positive half-wave of the mains voltage is supplied to the collector of the transistor VT1 through the diode VD1, and a negative half-wave is supplied to the transistor VT2 (through the diode VD2). At the same time, pulses from the output of the first generator on elements DD4, DD4 are sent to the bases of transistors through resistor R1.1 and capacitor C1.2.

When the output of the generator is a high logic level, the charging of the capacitor C4 will begin through the resistor R4 and the emitter junction of the transistor VT1. The transistor will open, the lower crystals of each LED in the first garland will glow. In this case, the VT2 transistor will be closed by a positive voltage (about 0,7 V) at the base, so the top LED crystals in the garland do not light up.

When a low logic level appears at the output of the generator, the discharge of the capacitor C4 through the resistor R4 and the emitter junction of the transistor VT2 will begin - it will open, the upper LED crystals will start to glow, and the lower ones will go out, since the transistor VT1 will be closed.

Other generators and switches work similarly. Since the frequencies of the generators differ from each other, the garlands are switched randomly.

It is permissible to install any other low-power transistors of the appropriate structure in the device with a maximum collector current of more than 30 mA and a permissible collector voltage of at least 30 V. Diodes VD1 - VD6 - any low-power rectifiers. VD8 must have a permissible reverse voltage of at least three times the voltage on the secondary winding of the transformer. The zener diode can be used for a voltage of 12 ... 15 V with a stabilization current of at least 10 mA. It is desirable to use LEDs with the largest possible radiation angle and made in a case made of transparent material with a lens - KIPD41A-KIPD41M, KIPD45A-KIPD45M. It is best to turn them on in a garland so that at each half-wave of alternating voltage they glow in one color.

Resistors - MLT, S2-33 of the corresponding power, oxide capacitors - K50-35 or similar, the rest - KM. K73.

The transformer must provide sufficient voltage on the secondary winding to power the selected number of LEDs in the garlands. For example, voltage Un = 1,8 ... 2.2 V drops on the LED, which means that to power a garland of ten LEDs, you need an alternating voltage on the secondary winding U „ = 10UA + + (4 ... 10 V). Additional voltage drops across the switch and quenching resistor R10.

If there is a ready-made transformer with a different voltage on the secondary winding, it is easy to determine the number of LEDs in the garland using the information given.

Most parts of the device are placed on a printed circuit board (Fig. 4) made of one-sided foil fiberglass. When checking the device, it is necessary to set the same values of the alternating current through the LEDs by selecting resistors R7-R9. To do this, the milliammeter is connected in series with the tested garland.

Switch of three garlands on two-color LEDs

If the fixed resistors R1 - R3 are replaced with trimmers, it will be possible to quickly select the most suitable operating mode for the generators.

If desired, you can achieve that, along with the color, the brightness of the LEDs also changes slightly, which gives a better effect. Then, after setting the frequency of the generators, you will have to select capacitors C4 - C6 of different capacities, and replace the transistors with more powerful ones, for example, KT815B - KT815G (VT1, VT3, VT5), KT814B - KT814G (the rest), and install them on small body taps.

Author: I.Nechaev

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