U.S. Philips Corporation

Henri A Melai

Adrianus M De Bijl

Antonius F Almering

The invention relates to a circuit arrangement for operating a lamp (LA), comprising means X for generating a current of alternating polarity, a load branch B coupled to the means X and provided with a series circuit Y comprising

Circuit arrangement

A DC-AC converter for supplying energy to a dishcarge lamp (17). The converter is in the form of an imcomplete half-bridge circuit (11, 12; 15, 16, 19, 18). The lamp (17) is connected in series with a coil (18) and a capacitor (16). Two switching elements (11, 12) in the half-bridge circuit are formed as semiconductor switching elements. The lamp current is a square-shaped alternating current. A diode (13) is connected in parallel with the one switching element (11) and a diode (14) is connected in parallel with the other switching element (12). The control circuit of the switching elements is provided with a switching circuit (21) which alternately switches the one switching element (11) and the other switching element (12) several times. The number of switching elements through which the lamp current flows can therefore remain limited to two.

DC-AC converter for supplying a gas and/or vapour discharge lamp

An arrangement for starting and supplying a discharge lamp (14) equipped with preheatable electrodes (15, 16). An electric coil (13) is arranged in series with the lamp and a capacitor (17) is arranged in parallel with the lamp. A voltage of a high frequency is first applied between the ends (A, B) of the series arrangement formed by the coil (13) and the lamp (14) whereafter approximately 1 second later said frequency is reduced until a series resonant condition is obtained and thereafter still further reduced to the operating frequency of the lamp. This starts the lamp (14) with the electrodes preheated to a sufficient extent.

Variable frequency start circuit for discharge lamp with preheatable

A DC/AC converter provided with two transistors (11 and 20) alternately conductive to supply current to an inductively stabilized discharge lamp (16, 15) to be connected to the converter. The lamp is connected in series with a primary winding (12) of a current transformer. A secondary winding (30, 31) of the transformer is connected to a timing circuit (32 to 35; 32' to 35') of a control device of the transistors. The timing circuit is provided with voltage-dependent elements, i.e. Zener diodes (35, 35'). The combination of the current transformer and the Zener diodes causes the frequency of the converter, during starting of the lamp, to be larger than during the operating condition of the lamp. This insures that the lamp electrodes are properly heated before the lamp ignites.

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Eindhoven, Netherlands

Henri A Melai