Dimmer Light

The dimmer is designed for a smooth change of brightness of conventional light bulbs with a total capacity of up to 1,000 watts.

The regulatory element of the scheme (Fig. 6.15) is an electronic switch - thyristor VS1 type T122-20-4 (T122-25-4), the control electrode that emits pulse opens voltage phase-shifted relative to the anode. From the moment of opening the thyristor (phase shift quantity) depends on the brightness of the lamp.

phase-shifting circuit consists of R6, R7 and C2. Once the voltage on the capacitor C2 to rise to the threshold of unijunction transistor VT1, it opens and the capacitor is discharged through the resistors R1 and R2. The brightness of the lighting changes the resistor R6.

Fig. 6.15. Schematic diagram dimmer

Fig. 6.16. Dimmer with a smooth increase of brightness

The circuit used resistors R1 ... R5, R7, R8 type MLT, R6 - SP - 4a, capacitors C1, C2-K73-17 250 V. Diodes VD1 ... VD4 use any high-voltage, a current valid no less than 10 A; VD5 VD6 and can be replaced by one zener diode, such as the type D816A. Thyristor VS1 is mounted on the radiator.

Reported in the scheme " * " elements may require selection when configuring. Resistor R7 adjusts the maximum voltage across the lamp at zero resistance R6.

shown in the diagram the dotted line LED can be omitted, but its presence makes it possible to know what is on the scheme, and the lamp is not lit due to the fact that control the brightness is reduced to zero.

The second diagram (Fig. 6.16) allows not only to regulate the voltage across the lamp, but also provides a smooth increase of brightness to a value set by a resistor R7. This significantly extends lamp life by eliminating congestion at the time of inclusion. Transient overload lamp arises from the fact that the filament has a cold resistance on the order of less than heated.

Setting the dimming circuit is similar to that already described above, for which the collector VT3 temporarily shorted to common wire - transistor VT2 is in saturation. After setting the dimmer, when the diode is off VD5, the selection of the nominal value of the resistor R10 are seeking to position in the dimmer " maximum " Lamp at dawn. Now you can connect a diode VD5 and verify operation of the device.

When you turn on the circuit (S1), when the controller (R7) is set to maximum brightness, glow lamps will gradually increase during the 1 ... 2 seconds.

Fig. 6.17. Triac dimmer on a smooth increase of brightness

A similar scheme can be performed on the Triac switch (Fig. 6.17). That allows to reduce dimensions of the device, since in this case does not need powerful rectifier diodes. The pulse transformer T1 is wound-wire PELSHO 0.12 ferrite ring size M4000NM K16h10h4 mm and contains the coil 1 - 80 turns, 2 - 60 turns. Before rolling, round off the sharp edges of the core needle files. Otherwise, they will be cut wire. After winding and coil impregnating varnish, you must make sure there is no leakage between the windings, and the coil and ferrite frame.

The electrolytic capacitor C2 must be used with a small leakage current, such as the type of K52-1. Find & compare Trimmer resistor R9 - 19a.

Figure 6.18

Option PCB layout for the circuit with a triac is shown in Fig. 6.18.

Used in circuits SCR and triac allow you to manage and more powerful load (2000 W), but in this case they should be set on the radiator.