Switch-Start Cicruit



       Figures 1-3 shows the switch-start fluorescent lamp circuit.

      A glow type starter switch is connected directly across the fluorescent lamp and contains two bimetallic strip electrodes and an inert gas enclosed in a glass bulb. The starter electrodes are normally open. When the supply voltage is switched on, current flows through the shock (inductor), lamp cathodes, and through the gas in the starter switch causes the strip electrodes to bend and make contact with each other, allowing a high current to pass through the lamp cathodes. This action heats up the cathode filaments and they emit a large cloud of electrons. Glow discharge in the starter switch ceases and the bimetallic electrodes cool down and reopen. A collapse in the magnetic field across the shock coils occurs which causes a large voltage surge to initiate the discharge between the cathode filaments. The chock now performs another function by limiting the current through the low resistance path inside the lamp.
     The function of the capacitor across the starter switch is to suppress any arc across the contacts (radio interference suppression). Due to a chock being incorporated in the circuit a power factor correction capacitor is connected directly across the a.c. supply.

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