The Choke coil of a tube light performs two functions. First it provides high voltage with the help of the starter. This lights up the type light and the gas inside it is ionized. After ionization of gas the starter gets separated from the circuit and the voltage across the choke coil drop. At this stage, about 60 to 70V are required to maintain the ionization of the gas. A tube light can be used even without the choke and the starter also. In principle a high starting voltage and a low operating voltage is required.
The circuit given here performs just this function. The circuit performs well within the supply range of 70V to 270V. The heart of the circuit is the bridge rectifier circuit built by the diodes Dl to D4 and the two capacitors Cl and C2 connected to it. When all these components are put together as shown in the diagram and then AC Supply is received by the circuit because of the 100W/230V bulb connected in series, This supply rises with the charging of the capacitors Cl and C2 and reaches about 600V. The gas inside the tube light gets immediately ionized due to his high voltage. After ionization, the tube gets a supply of 110V DC. The flow of the current in the ionized gas depends upon the requirements of the tube in order to keep the gas ionized. The series bulb glows very dim and consumes very ,little power.