halogen lamp protector

69halogen lamp protector Halogen lamps are, unfortunately, rather prone to burn out when they are switched on, and this is mainly owing to the high current consump- tion of these devices during the in- itial stage of heating up to the normal operating temperature of the filament in haloid gas. A typical value for the cold resist- ance of a 6 V- 4 W halogen lamp is about 0.3 ohm, demanding a turn-on current of 20 A. In view of the rela- tively low internal resistance of car and motor-cycle batteries, such a current surge is not at all to be dismissed as purely theoretical, and it is easily seen that the ensuing rapid heating inside the lamp is a prime cause for the thin filament to melt at the sudden temperature effect. What is required, therefore, is a series regulator system to limit the current during the heat-up phase; in other words, a soft turn-on facility. The circuit diagram shows that Ci is charged to the battery voltage by means of Ri and R2, causing FET Ti to become slow...