Lighting brightness control. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Lighting brightness control. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Lighting

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The dimmer is designed to smoothly change the brightness of conventional lighting lamps with a total power of up to 1000 W.

The regulating element of the circuit (Fig. 1) is an electronic switch - thyristor VS1 type T122-20-4 (T122-25-4), the control electrode of which receives opening voltage pulses, phase-shifted relative to the anode. The brightness of the lamp depends on the moment the thyristor opens (the magnitude of the phase shift).

Fig.1 (click to enlarge)

The phase shifting circuit consists of R6, R7 and C2. As soon as the voltage on capacitor C2 increases to the operating threshold of the unijunction transistor VT1, it opens and the capacitor is discharged through resistors R1 and R2. The brightness of the lighting is changed by resistor R6.

The circuit uses resistors R1...R5, R7, R8 type MLT, R6 - SP--4a, capacitors C1, C2-K73-17 for 250 V. Diodes VD1...VD4 are suitable for any high voltage, with a permissible current of at least 10 A; VD5 and VD6 can be replaced with one zener diode, for example type D816A. Thyristor VS1 is installed on the radiator.

Elements marked “*” in the diagram may require selection during setup. Resistor R7 adjusts the maximum voltage across the lamp with zero resistance R6.

The LED shown in the dotted line in the diagram may not be installed, but its presence allows you to know that the circuit is turned on, and the lamp does not light due to the fact that the brightness of the light is reduced to zero by the regulator.

The second circuit (Fig. 2) allows you not only to regulate the voltage on the lamp, but also ensures a smooth increase in the brightness of the glow to the value set by resistor R7. This significantly extends the life of the lamp by eliminating overload at the moment of switching on. A short-term lamp overload occurs due to the fact that the filament in a cold state has an order of magnitude less resistance than a heated one.

Fig.2 (click to enlarge)

Setting up the brightness control circuit is carried out similarly to that already described above, for which we temporarily short-circuit the VT3 collector to the common wire - the VT2 transistor will be in saturation. After adjusting the brightness control, with the VD5 diode turned off, by selecting the value of the resistor R10, we ensure that when the brightness control is in the “maximum” position, the lamp glows slightly. Now you can connect the VD5 diode and check the operation of the device.

When the circuit (S1) is turned on, if the regulator (R7) is set to maximum brightness, the lamp glow will gradually increase within 1...2 seconds.

A similar circuit can be made on a triac switch (Fig. 3). This makes it possible to reduce the dimensions of the device, since in this case powerful rectifier diodes are not needed. The T1 pulse transformer is wound with PELSHO-0,12 wire on a ferrite ring M4000NM of standard size K16x10x4 mm and contains 1 - 80 turns in the winding, 2 - 60 turns. Before winding, we round off the sharp edges of the core with a needle file. Otherwise they will cut the wire. After winding and impregnating the coil with varnish, you need to make sure that there is no leakage between the windings, as well as the winding and the ferrite of the frame.

Fig.3 (click to enlarge)

Electrolytic capacitor C2 must be used with a small leakage current, for example type K52-1. Trimmer resistor R9 type SP-19a.

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