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This voltage drives a resonant LC tank circuit so as to produce a filtered sinusoidal AC signal which is applied to the lamp.
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This DC voltage is then converted to high frequency AC square wave voltage using a set of switches. Electronic Ballast to start a Fluorescent lampĪ typical Electronic ballast circuit consists of an AC to DC converter comprising of bridges and capacitors which rectify the AC signal to DC and filter out AC ripples to produce DC power. Using Electronic ballast to start the Fluorescent lampsĮlectronic ballasts, unlike magnetic ballast provide the AC current to the lamp after increasing the line frequency from about 50 Hz to 20KHz. They cause flickering as they work at lower frequenciesĢ.The power consumption is quite high, about 55 Watt.
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Ħ Reasons why Magnetic ballast is not considered convenient?
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This causes a collapse in the magnetic field across the coil and as a result a high voltage is produced which provides the required triggering to heat the lamp so as to produce the adequate amount of free electrons through the inert gas and eventually the lamp glows. As one of the electrode is a bimetallic strip, it bends as it gets heated and eventually the arc is completely eliminated and as no current flows through the starter it acts as open switch. As the current passes through the filament to the electrodes of the bulb (used as a starter switch), an electric arc is formed between the two electrodes of the bulb. This current while passing through the filaments of the tube heat them slowly so as to cause production of free electrons. Initially for each half cycle of the AC signal, the current flows through the ballast (coil), developing a magnetic field around it. As current increases the magnetic field increases and this eventually opposes the flow of current. As AC current passes through the coil, magnetic field is produced. The ballast used is magnetic ballast which consists of a transformer coil. The starter switch used is a typical bulb consisting of two electrodes such that an electric arc is formed between them as current flows through the bulb. Without a starter switch and ballast, a high amount of current would flow directly to the lamp, which would reduce the resistance of the lamp and eventually heat up the lamp and destroy it.įluorescent lamp using a magnetic ballast and a starter switch The ballast is used to limit the amount of current flowing through the lamp. The starter switch is required to preheat the lamp so that considerable less amount of voltage is required to trigger the production of electrons from the electrodes of the lamp. One of the methods is using a starter switch and a magnetic ballast to provide the flow of ac current to the lamp. Two starting mechanisms for a Fluorescent lampġ. For this reason a special starting mechanism is needed to introduce more free electrons in the gas. Normally there are very few free electrons and ions in the gas. There needs to be an abundance of free electrons and ions to allow flow of charge through the gas. In Fluorescent lamps the current flows through a gaseous conductor, instead of a solid state conductor where electrons simply flow from negative end to the positive end. When this light strikes the phosphor coated on the tube, it excites the electrons of phosphor to higher level and as these electrons fall back to their original level, photons are emitted and this light energy is now in form of visible light. This emitted light energy is in the form of ultraviolet light, which is not visible to humans. As the electrons collide with the gaseous atoms of mercury, they give away free electrons which jump to higher levels and when they fall back to their original level, photons of light are emitted. Fluorescent lamp How does a Fluorescent lamp works?Īs electricity is supplied to the tube through the electrodes, the current passes through the gas conductor, in form of free electrons and ions and vaporizes the mercury.