The fluorescent tube-light requires additional gear such as the copper ballast and starter for normal operation. These two are required to provide the initial high voltage for ionization and thereafter to limit the current through the tube to safe values.
It has been observed that the illumination efficiency of the tube-light when excited by high frequency power source is higher than that when excited at the 50Hz line frequency. Moreover, the power factor and the efficiency of the bulky copper ballasts are poor. Hence, electronic ballasts were developed to overcome these deficiencies.
The electronics ballast circuit is light in weight, compact and has a high power factor. It starts up even at low voltage, and above all has a very high efficiency.
The typical electronic ballast is a current fed oscillator in the half bridge configuration. Transistors T1, T2 and capacitors C5, C6 form the half bridge in the circuit electronic ballast for tube light. Diodes D8, D9, D5, D6 clamp the output voltage values within the supply rails. Diodes D1 to D4 and capacitors C1 to C3 provide the required DC voltage for the circuit. Transformer X2 regulates the current through the tube and also determines the frequency of operation of the electronic ballast. For the value shown, the operating frequency is typically 25 to 30 kHz, R6, C4 and DIAC1 (DB-3) from the start-up circuit.