Billboard dimmer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting
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To attract customers, shops and all kinds of organizations use illuminated advertising in the form of hung bright lights and inscriptions. It is good if it is a solid organization in which a specially appointed person controls the switching on and off of outdoor advertising. And if there is no one to do this, then often there is an unjustified waste of electricity. Replacing lamps in billboards is not an easy procedure, and if it is a "durolight" light cord, in which the burned-out bulbs do not change at all, then even worse. To increase the life of the lamps, it is good to reduce the brightness of their glow. For these purposes, the well-proven scheme [1] was modified. In addition to the smooth adjustment of the load voltage, it provides for turning off the load in the morning and turning it on in the evening.
Rice. 1. Schematic diagram of a billboard dimmer
Consider the operation of the device (Fig. 1). The mains voltage (220 V) is extinguished on capacitance C1, rectified by diodes VD1, VD2, smoothed by capacitor C2 and stabilized by a zener diode VD3 at a level of approximately 9 V. The entire circuit is powered from this voltage. The pulse shaper (at the moment the mains voltage passes through zero) is assembled on transistors VT1, VT2 and resistors R2 ... R4. At the moment the voltage passes through zero, a negative pulse is formed at the input 6 of the DD1.2 element. If the photodiode VD4 is illuminated, then the zero level is set at the output DD1.1, which prohibits the passage of pulses from the shaper. At output 4 DD1.2 - zero level, and the transistor VT3 is closed. At night, output 3 DD1.1 is set to logical "1". Pulses from the shaper open the transistor VT3 for about 0,5 ... 1 ms. Capacitor C4 is charged to the level of the supply voltage. Then it is smoothly discharged through the R7-R8 chain. The voltage on C4, reaching the level of logic "O", switches the elements DD1.3, DD1.4.
The zero level at the output 11 DD1.4 charges the capacitor C5. During charging, the transistor VT4 closes, and VT5 opens and turns on the thyristor VS1. The duration of the pulses on the control electrode VS1 depends on the parameters of the chain C5-R9 and is 10...20 µs. At the next zero crossing, the cycle repeats. The advantage of this scheme is that the triac opening frequency remains unchanged, and a change in the mains voltage does not affect the regulation process.
The following parts are used in the device. Capacitors C1, C3, C4 - type K73-17, C2 - K50-35, C5 - KM6. Resistor R6 - type SP3-1, R7 - SP-04, the rest - MLT. As VD1, KD509, KD510, KD209 with a permissible voltage of 25 ... 50 V and a current of 100 ... 200 mA are suitable. Instead of D814B, any zener diodes with a stabilization voltage of 8 ... 15 V are suitable.
Instead of KT315, you can use KT312, KT316, KT201, KT3102, instead of KT361 - KT203, KT209, KT3107. Photodiode FD263 is replaced by FD 320.
If it is necessary to switch significant power, the triac must be installed on a radiator, or a more powerful one, for example, TC2-25, should be used.
The dimmer is assembled on a single-sided printed circuit board 1,5 ... 2 mm thick and 40x70 mm in size (Fig. 2).
Rice. 2. Printed circuit board and layout of the billboard dimmer elements
When adjusting with resistor R6, it is necessary to select the threshold for turning on / off the load, and with resistor R7 - the brightness of the glow. For normal operation of the device and prevention of relaxation oscillations, a black cambric 20 ... 30 mm long is put on the photodiode and directed away from advertising bulbs and bright lanterns.
Literature
- S. Biryukov. Triac power regulators. - Radio, 1996, N1, p.44.
Author: S.Abramov, Orenburg, asmorgen@mail.ru; Publication: radioradar.net
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