A resonant L-C circuit is series-excited from an AC voltage source and intended to be parallel-loaded with a load that, for some reason or another, may be disconnected or otherwise inoperative. For efficiency reasons, the unloaded circuit Q-factor may be about 50 times higher than the loaded Q-factor; which implies that, if the load were to become inoperative, the power drawn by the L-C circuit from the source, and the voltage/current magnitudes developed in the L-C circuit, would be 50 times larger than when the load is operative. To prevent unnecessary power drain and/or to avoid damage to source and/or circuit components, which damage may occur even if the L-C circuit is left unloaded for but a very brief period, a circuit protector is provided. This circuit protector comprises: (i) a Varistor to provide an absolute limit on the maximum attainable magnitudes of power, voltage and current, thereby clearly protecting the source and the L-C circuit, and (ii) means operative to protect the Varistor from overloading as well as to prevent unnecessary power drain, which means provides for an intermittently interrupted short circuit across the tank-capacitor in case current flows through the Varistor for more than a very brief period of time. With the tank-capacitor shorted, the resulting power drawn from the source will be of negligible magnitude.

An electronic operating device for discharge lamps is disclosed in which an output terminal is connected via a coupling capacitor (CB) to a reference potential (E). An electric component (VC) which acts as a voltage source is inserted in series with the coupling capacitor (CB) in order to reduce the potential of an output terminal. The electric component (VC) consists in one embodiment of an inductor which is coupled to the lamp inductor.

A discharge lamp lighting device combines one or more discharge lamps and a backswing booster including essentially a power source circuit having a power source connected in series with a ballast and a high voltage generating circuit having an oscillation capacitor and a series circuit of a nonlinear inductor and a switching semiconductor. The supply voltage for the discharge lamp from the power source circuit is established to the extent permissible by the lower limit for sustaining an arc discharge of the lamp so that the terminal voltage of the ballast in the lamp operation is maintained as low as possible. The preferred backswing booster is of small size and an impedance circuit having a capacitor either with or without a bias coil is added to the high voltage generating circuit to produce a momentary high voltage. A leakage transformer or a voltage transformer with a tap or with a supplemental winding may be coupled to the power source circuit to establish a specified potential point from which voltage for the high voltage generating circuit is supplied to reduce the applied voltage during the lamp operation. An economical lighting device for the sequential ignition of two discharge lamps by means of a single high voltage generating circuit is disclosed.

The invention relates to a capacitively stabilized discharge lamp shunted by a coil. During the starting procedure of the lamp the coil is brought into saturation so that, by means of resonance with the capacitive ballast, a high voltage is applied across the lamp to start it. The B-H magnetization curve of the coil has been chosen so that a transition from the unsaturated condition to the saturated condition also occurs during the operating condition of the device, namely just before the lamp is extinguished during each half cycle of the a.c. supply voltage. Consequently the ratio of the r.m.s. voltage of the a.c. voltage source to the operating voltage of the lamp may be relatively small. A resistor having a positive temperature coefficient shunts the lamp and is in series with the coil so as to limit the electric current if the lamp refuses to start.