It is no secret that the halogen lamps used in cars, often fail. This is the result of inrush current, which inevitably occurs every time when enabled, when the spiral filament is still in the cold (cold) state.
For example, “halogen” fog lights are designed to work in normal mode with a consumption of 55-watt capacity (the 12-volt power supply). In accordance with known to every student-the student law for the electric circuit, the resistance of the filament should be about 2.6 Ohms. And in fact this is true, but only when heated filament. The cold lamp resistance measured by ohmmeter, is slightly more than 0.2 Ohm. This means that at the moment when this “galogenki” it will be with all the inevitable take place 60 amp inrush current!
To extend the service life of filament lamps in low voltage, and designed my proposed device. The time for a smooth warm-up — output lamp in the operating mode depends on the resistance of the resistor 141 and the capacitance of the capacitor C1. If specified in the diagram the values does not exceed 2.5 s.
The saturation voltage of the composite transistor VT1 — VT2 can be set by regulation of the rotor resistor R2. This allows you to choose the desired time mode (depending on power load) in the range from zero to the maximum delay.