Arrangement for dimming at least two parallel-arranged discharge lamps

Claim 2

An arrangement for supplying an alternating current to at least two parallel arranged discharge lamps with means for stepwise dimming of said lamps comprising, a pair of AC supply terminals coupled to said lamps, n ballast impedances connected in circuit with a first one of said lamps and another n ballast impedances connected in circuit with a second one of said lamps, wherein n comprises at least two ballast impedances for each lamp, a first group of (n-1) bridge rectifiers connected to said first lamp and a second group of (n-1) bridge rectifiers connected to said second lamp, means connecting two face-to-face diagonal points of each bridge rectifier of the first group to the coRresponding diagonal points of a corresponding bridge rectifier of the second group to provide two such connections for each corresponding pair of bridge rectifiers of the first and second groups, (n-1) switching elements, each of said two connected together through a respective switching element, and means connecting the third and the fourth diagonal points of each bridge rectifier in series with one of the ballast impedances and in a branch shunted by one of the other ballast impedances.

Claim 3

An arrangement as claimed in claim 1, wherein the ballast impedances for each lamp are connected in series.

Claim 4

An arrangement as claimed in claim 1 comprising at least three ballast impedances for each lamp and wherein the switching elements in the connection branches of the bridge rectifiers are free from mutual couplings so that the number of dimming steps for each lamp is greater than the number of ballast impedances for each lamp.

Claim 5

A ballast suitable for an arrangement as claimed in claim 1 and provided with a housing accommodating at least two of said ballast impedances, characterized in that the housing includes a bridge rectifier which is connected in series with one of said ballast impedances and which is present in a branch shunted by the other ballast impedance.

Claim 6

A lighting system for a plurality of discharge lamps comprising, first and second supply conductors adapted for connection to a source of AC current, and means for coupling said lamps in parallel across said first and second supply conductors comprising, a group of n ballast impedances for each of said lamps wherein n comprises at least two ballast impedances per lamp, a plurality of diode bridges arranged in groups of (n-1) bridges for each lamp with each bridge arranged to pass an AC current through a first pair of diagonal bridge terminals, circuit means connecting said lamps to the supply conductors comprising means connecting said first pair of bridge terminals of each diode bridge in series with one of the ballast impedances and in shunt with another one of the ballast impedances of the associated group of impedances and diode bridges, means connecting a second pair of bridge diagonal terminals of each diode bridge of one group of bridges to the corresponding second pair of bridge diagonal terminals of corresponding ones of the diode bridges of a second bridge group, (n-1) switching elements, and means individually connecting each of said switching elements to the second pair of bridge terminals of a respective diode bridge in a manner to selectively interconnect said terminals of the respective diode bridges to adjust the current in steps in said lamps and thereby vary the lamp illumination.

Claim 7

A lighting system for a plurality of discharge lamps comprising, first and second supply conductors adapted for connection to a source of AC current, and means for coupling said lamps in parallel across said first and second supply conductors comprising, a group of n ballast impedances for each of said lamps wherein n comprises at least two ballast impedances per lamp, a plurality of diode bridges arranged in groups of (n-1) bridges for each lamp with each bridge arranged to pass an AC current through a first pair of diagonal bridge terminals, circuit means connecting said lamps to the supply conductors comprising means connecting said first pair of bridge terminals of each diode bridge in series with one of the ballast impedances and in shunt with another one of the ballast impedances of the associated group of impedances and diode bridges, means connecting a second pair of bridge diagonal terminals of each diode bridge of one group of bridges to the corresponding second pair of bridge diagonal terminals of corresponding ones of the diode bridges of a second bridge group, (n-1) switching elements, and means individually connecting each of said switching elements to the second pair of bridge terminals of a respective diode bridge in a manner to selectively interconnect said terminals of the respective diode bridges to adjust the current in steps in said lamps and thereby vary the lamp illumination.

Claim 8

A system as claimed in claim 5 wherein said circuit means comprises means connecting the ballast impedances of each group in series between one supply conductor and one terminal of its respective lamp and means connecting said first pair of bridge terminals of each diode bridge of its group to the terminals of its respective shunt impedance.

Claim 9

A system as claimed in claim 5 wherein said circuit means comprises means connecting a first ballast impedance of each group between one supply conductor and one terminal of its respective lamp, and means connecting each series combination of a ballast impedance and a first pair of terminals of a diode bridge of each group in parallel with the said first ballast impedance of its associated group.

Claim 10

A system as claimed in claim 6 which comprises at least three ballast impedances for each lamp and at least two switching elements which can be selectively operated to provide a greater number of current steps for each lamp than the number of lamp ballast impedances with a minimum of four such current steps in the case of three ballast impedances per lamp.

Claim 11

A system as claimed in claim 7 which comprises at least three ballast impedances for each lamp and at least two switching elements which can be selectively operated to provide a greater number of current steps for each lamp than the number of lamp ballast impedances with a minimum of four such current steps in the case of three ballast impedances per lamp.

Claim 12

A system as claimed in claim 5 wherein said circuit means comprises means connecting first and second ballast impedances of each group in series between one supply conductor and one terminal of its respective lamp and means directly connecting said first pair of terminals of a diode bridge of each group to the terminals of one of the impedances of its respective group.