Lamps will last longer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting
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It's no secret that halogen lamps used in cars often fail. This happens as a result of a surge of current that inevitably occurs every time it is turned on, when the filament helix is still in an unheated (cold) state.
For example, the "halogen" fog lamps are designed to operate in normal mode with a power consumption of 55 watts (with a 12-volt supply). In accordance with the law known to every high school student for an electrical circuit, the resistance of the filament should be about 2,6 ohms. And in fact this is so, but only with a heated filament. In a cold lamp, the resistance measured with an ohmmeter is slightly more than 0,2 ohms. And this means that at the moment this "halogen" is turned on, a 60-ampere current surge will inevitably take place in it!
To extend the life of incandescent lamps in a low-voltage network, the device I propose is intended. The time of smooth warm-up - the output of the lamp to the operating mode - depends on the resistance of the resistor R1 and the capacitance of the capacitor C1. With the ratings indicated on the diagram, it does not exceed 2,5 s.
The saturation voltage of the composite transistor VT1 - VT2 can be set by adjusting the rotor of the resistor R2. This allows you to select the required time to enter the mode (depending on the load power) in the range from zero to the maximum delay.
The choice of KT872A as a power semiconductor triode is not accidental. This transistor manufactured by NPO Transistor (Minsk) is capable of withstanding significant current surges at 1 to 10 A for a long time. lamp, up to 972 A.
If the SA1 switch is replaced with a jumper, and a micro toggle switch or a micro button is connected in series with the resistor R1, then additional convenience appears - the absence of a powerful power switch. His role will now be performed by a power transistor.
Due to the small number of parts used in this device, the printed circuit board is missing. All installation is carried out by a hinged method (reliable and well known to everyone from school laboratory work in physics).
Author: A.Filipovich
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