It's no secret that halogen lamps are used in cars, often overlook out of action. This occurs as a result of inrush current resulting from the fact that the spiral filament lamp in a cold state, has a low resistance.
Here is a vivid example: automotive halogen lamp used in fog lamps consume in normal mode 55 W (with 12 V power supply), therefore, the resistance of the filament when heated will be about 2.6 Ohms. In fact, the resistance measured by the ohmmeter, a little exceed 0.2 Ohms. As a result, the inrush current will be 60!
To extend service incandescent lamps in cars and other low-voltage equipment and serves as the proposed device.
The time for a smooth heat - output lamp on mode depends on the resistance resistor R1 and the capacitance of the capacitor C1, and when indicated in the diagram the values of is about 2.5 s. the saturation Voltage of the composite transistor VT1, VT2 you can set the rotation of the rotor of the resistor R2. This allows you to pick up the necessary time of entering the mode, depending on load power in the interval from zero to the maximum delay.
Transistors VT1 and VT2 need set on the total heat sink surface area of about 100 cm2, at a current consumed lamp until 6 A. selection of the power transistor CTA not random. This transistor NPO "Transistor" (Minsk) able to withstand a long time significant inrush current when the average current up to 10 A.
If the switch SA1 replace bridge and in series with the resistor R1 to turn on microtuber or microcopy - there is an additional convenience-no power switch. It now performs the role of the power transistor.
Author: A. Filipovic, Dzerzhinsk, Minsk region