1 Introductory notes

Gas discharge lamps, this meaning lamps using the principle to make a gas electrically conductive and thereby light emitting, are a relatively old technique. Especially fluorescent lamps represent a very widespread lighting system. It is not possible to apply the line voltage directly to such lamp, be it AC or DC, a higher or a lower magnitude. Traditionally these lamps have always been operated on AC mains by means of a so-called magnetic ballast, which is nothing more than a reactor or choke, for limiting the lamp current. In recent years, as power electronics techniques came up, an alternative way of operation was introduced, the so-called electronic ballast, which converts the incoming mains frequency into a much higher frequency, usually in the range of 20 kHz to 80 kHz, to operate the lamp with.

The magnetic ballast method creates a huge amount of inductive reactive power, significantly exceeding the magnitude of active power, but this reactive power can easily and cheaply be compensated without risk of any interferences, if done adequately (see section 5). The electronic ballast does not – or should not – produce substantial amounts of fundamental reactive power (displacement power factor DPF or cosφ). It need not but may be designed to operate on different mains frequencies, including DC, and different voltages, thereby also compensating any input voltage variances. The decisive argument put forward for its use is, however, the energy saving achieved, not so much by lower internal losses in the ballast itself, but rather by an efficiency improvement of the lamp when operated at the high frequency supplied from the output terminals of such electronic ballast. For this reason they feed less power into the lamp than a magnetic ballast does. However, electronic ballasts are several times more expensive than the plain passive magnetic models and much more susceptible to certain disturbances and are likely to become themselves a source of disturbances. Unlike the magnetic ballasts, which as a law of physics can follow only one principle of working and only one basic design, power electronics provide a lush choice of design variants and working principles to design electronic circuits for operating fluorescent lamps.