Arrangement provided with a gas and/or vapour discharge lamp

Claim 2

An arrangement for energizing an electric discharge lamp having a pair of electrodes for defining a current path through the lamp comprising, a pair of input terminals for supplying an operating voltage to said arrangement, a controlled switching element connected in series circuit with the lamp across said input terminals of the arrangement, a control device coupled to a control electrode of the switching element for switching the switching element on and off at a minimum frequency of 400 times per second, an inductor connected in a branch circuit in parallel with said lamp so that currents flow in parallel through the lamp and the inductor in the operative condition of the lamp and with the switching element conductive, and means responsive to the cut off of current in the switching element for generating a voltage across the lamp which is at least equal to the re-ignition voltage of said lamp.

Claim 3

An arrangement as claimed in claim 1 wherein the inductor comprises the means for generating the voltage for the re-ignition of the lamp, the combination of the value of the inductance L of said inductor and of the current variation di/dt of the current i through said inductor at the moment the switching element becomes cut off being chosen so that the product L. di/dt is at least equal to said lamp re-ignition voltage.

Claim 4

An arrangement as claimed in claim 2, wherein said input terminals are adapted for connection to a direct voltage supply, the inductance of the inductor being chosen so that the value of the product of the conductivity period of the switching element and the mean lamp current during said conductivity period is between 0.8 times and 1.2 times the value of the product of the off-time of the switching element and the mean lamp current during said off-time.

Claim 5

An arrangement as claimed in claim 2 in which the lamp comprises a low-pressure mercury vapour discharge lamp provided with two preheated electrodes and the inductor connects the ends of the electrodes remote from the input terminals.

Claim 6

An arrangement as claimed in claim 2, wherein the switching element comprises a transistor.

Claim 7

An arrangement as claimed in claim 2 wherein said input terminals are adapted for connection to an alternating voltage supply of approximately 40 to 60 Hz, characterized in that the switching element includes a rectifier bridge having a central branch including a transistor.

Claim 8

An arrangement as claimed in claim 2 wherein said input terminals are adapted to be connected to a voltage supply whose voltage is lower than the ignition voltage of the lamp, characterized in that the inductance of the inductor and the value of di/dt is chosen so that with the supply voltage applied to the input terminals of the arrangement but with the lamp not yet ignited the voltage generated in the inductor becomes at least equal to the ignition voltage of the lamp when the switching element is cut off.

Claim 9

Apparatus for energizing an electric discharge lamp comprising, a pair of input terminals for connection to a source of supply voltage, a controlled switching element connected in series circuit with the lamp across said input terminals, means coupled to a control electrode of the switching element for switching the switching element on and off at a frequency substantially higher than the supply voltage frequency, and an inductor connected in parallel with the lamp whereby currents flow in parallel through the lamp and the inductor in the operative condition of the lamp and with the switching element conductive, said inductor being chosen to generate a voltage which is at least equal to the lamp reignition voltage when the switching element is cut off and of a polarity to drive a current through the lamp in a direction opposite to that which flowed in the lamp during the conductive period of the switching element.

Claim 10

Apparatus for energizing an electric discharge lamp comprising, a pair of input terminals for connection to a source of supply voltage, a controlled switching element connected in series circuit with the lamp across said input terminals, means coupled to a control electrode of the switching element for switching the switching element on and off at a frequency substantially higher than the supply voltage frequency, and an inductor connected in parallel with the lamp whereby currents flow in parallel through the lamp and the inductor in the operative condition of the lamp and with the switching element conductive, said inductor being chosen to generate a voltage which is at least equal to the lamp reignition voltage when the switching element is cut off and of a polarity to drive a current through the lamp in a direction opposite to that which flowed in the lamp during the conductive period of the switching element.

Claim 11

Apparatus as claimed in claim 8 wherein the input terminals are adapted to be connected to a source of DC voltage and said switching means drives the switching element with a duty cycle such that the average ratio between the on and off time of the switching element is 3 to 5.

Claim 12

Apparatus as claimed in claim 8 wherein the input terminals are adapted to be connected to a source of DC voltage and the frequency of said switching means and the inductance of said inductor are chosen so that the product of the on-time lamp current and the on-time of the switching element is approximately equal to the product of the off-time lamp current and the switching element off-time.

Claim 13

Apparatus as claimed in claim 8 wherein the input terminals are adapted to be connected to a source of DC voltage and further comprising means directly connecting the inductor to the terminals of the lamp so that the DC supply current can flow in parallel through the lamp and the inductor during the on-time of the switching element.

Claim 14

Apparatus as claimed in claim 8 further comprising means responsive to the current flow through the switching element for deriving a control voltage proportional thereto, and means for applying said control voltage to said switching means whereby the switching means adjusts the duty cycle of said switching element as a function of the control voltage so as to maintain the lamp current approximately constant.

Claim 15

Apparatus as claimed in claim 8 wherein the lamp includes a pair of preheated electrodes connected to the inductor so that the inductor provides a path for current flow from the input terminals through the preheated electrodes and the switching element during the period prior to the ignition of the lamp.

Claim 16

Apparatus as claimed in claim 8 further comprising means directly connecting the inductor to the terminals of the lamp so that a DC supply current can flow in parallel through the lamp and the inductor during the on-time of the switching element, and the inductor is substantially free of magnetic coupling to other inductors.