Arrangement for igniting a gas and/or vapour discharge lamp provided with preheatable electrodes

Claim 2

An ignition circuit for a discharge lamp provided with preheatable electrodes comprising, two input terminals adapted to be connected to an alternating voltage supply source, a stabilizing ballast inductor, means connecting the series arrangement of the stabilizing ballast inductor and the lamp across said input terminals, a starter circuit for the discharge lamp comprising, a transistor, means connecting the transistor to the ends of the lamp preheatable electrodes remote from the input terminals, means connecting the base of the transistor to a control circuit having means for switching the transistor alternately conducting and non-conducting at a frequency substantially higher than the frequency of the AC voltage source during the ignition procedure of the lamp, a further electrical switching element connected in a branch circuit arranged in parallel with the transistor and provided with an operating member by means of which said switching element is triggered into a conducting condition thereby suppressing the switching operation of the transistor during the ignition procedure at a time no later than during the first half of each half cycle of said AC supply voltage, said further switching element remaining conductive for the remainder of each half cycle during the ignition procedure.

Claim 3

An ignition circuit as claimed in claim 1 wherein the operating member of the further electrical switching element is chosen so that per half cycle of the AC voltage supply the ratio between the period that the transistor is being switched and the total period of the half cycle is in the range between 0.0l and 0.5.

Claim 4

An ignition circuit as claimed in claim 1 wherein the further electrical switching element comprises a controlled semiconductor element and said operating member includes a glow discharge tube connected to the control electrode of the conrolled semiconductor element.

Claim 5

An ignition circuit as claimed in claim 1 further comprising a rectifier bridge, means connecting the ends of the preheatable electrodes remote from the input terminals to the transistor by means of said rectifier bridge, means connecting a control circuit having a short time constant to two output terminals of said rectifier bridge, means connecting the base of the transistor to said control circuit through a breakdown element, characterized in that the further electrical switching element comprises a semiconductor switching element having a first main electrode and a control electrode connected to one output terminal of the rectifier bridge in a manner such that the main electrode is connected directly thereto and the control electrode is connected thereto through a resistor, and means connecting the other main electrode of the semiconductor switching element to the other output terminal of the rectifier bridge.

Claim 6

An ignition circuit as claimed in claim 4, characterized in that the further electrical switching element is a thyristor.

Claim 7

An electric supply circuit for an electric discharge lamp having a pair of preheatable electrodes comprising, a pair of inpuT terminals for applying an AC supply voltage of a given frequency to the supply circuit, a ballast impedance, means connecting the ballast impedance in series with the discharge lamp across said input terminals, a combination heating and ignition circuit for the discharge lamp comprising, a first controlled semiconductor switch, means connecting said first semiconductor switch to the lamp electrodes to form a heating circuit for the electrodes that allows a heating current to flow from the input terminals to the lamp electrodes when said first semiconductor switch is turned on, a control circuit energizable from said input terminals and coupled to the control electrode of said first semiconductor switch and including means for alternately triggering the first semiconductor switch on and off at a frequency substantially higher than said AC given frequency and during the early part of each half cycle of said AC supply voltage, a second controlled semiconductor switch connected in a branch circuit across said first semiconductor switch for controlling the switching operation of the first semiconductor switch by effectively overiding said control circuit triggering means, and actuating means coupled to the control electrode of the second semiconductor switch for controlling the operation thereof whereby the switching operation of the first semiconductor switch is terminated at a time no later than during the first half of each half cycle of said AC supply voltage.

Claim 8

An electric supply circuit for an electric discharge lamp having a pair of preheatable electrodes comprising, a pair of inpuT terminals for applying an AC supply voltage of a given frequency to the supply circuit, a ballast impedance, means connecting the ballast impedance in series with the discharge lamp across said input terminals, a combination heating and ignition circuit for the discharge lamp comprising, a first controlled semiconductor switch, means connecting said first semiconductor switch to the lamp electrodes to form a heating circuit for the electrodes that allows a heating current to flow from the input terminals to the lamp electrodes when said first semiconductor switch is turned on, a control circuit energizable from said input terminals and coupled to the control electrode of said first semiconductor switch and including means for alternately triggering the first semiconductor switch on and off at a frequency substantially higher than said AC given frequency and during the early part of each half cycle of said AC supply voltage, a second controlled semiconductor switch connected in a branch circuit across said first semiconductor switch for controlling the switching operation of the first semiconductor switch by effectively overiding said control circuit triggering means, and actuating means coupled to the control electrode of the second semiconductor switch for controlling the operation thereof whereby the switching operation of the first semiconductor switch is terminated at a time no later than during the first half of each half cycle of said AC supply voltage.

Claim 9

A supply circuit as claimed in claim 6 wherein said actuating means is chosen to trigger the second semiconductor switch at a time in each half cycle of the AC supply voltage such that the switching period of the first semiconductor switch is between 1/20 and 1/5 of a half period of said AC voltage.

Claim 10

A supply circuit as claimed in claim 6 further comprising current rectifying means connected between the lamp electrodes and the combination heating and ignition circuit whereby the combination circuit is energized with a DC voltage but the lamp electrodes are heated with an AC current, and wherein said actuating means triggers said second semiconductor switch into conduction for terminating the switching operation of the first semiconductor switch and said second semiconductor switch continues to conduct substantially for the remaining part of each half cycle of the AC supply voltage subsequent to the trigger time thereby providing a heating current path for the lamp electrodes through the second semiconductor switch.

Claim 11

A supply circuit as claimed in claim 7 further comprising current rectifying means connected between the lamp electrodes and the combination heating and ignition circuit whereby the combination circuit is energized with a DC voltage but the lamp electrodes are heated with an AC current, and wherein said actuating means triggers said second semiconductor switch into conduction for terminating the switching operation of the first semiconductor switch and said second semiconductor switch continues to conduct substantially for the remaining part of each half cycle of the AC supply voltage subsequent to the trigger time, and said second semiconductor switch is coupled to the control electrode of the first semiconductor switch whereby conduction in the second switch holds the first switch in conduction to provide a heating current path for the lamp electrodes through the first semiconductor switch.

Claim 12

A supply circuit as claimed in claim 6 wherein said actuating means triggers said second semiconductor switch into conduction for terminating the switching operation of the first semiconductor switch and said second semiconductor switch continues to conduct substantially for the remaining part of each half cycle of the AC supply voltage subsequent to the trigger time.

Claim 13

A supply circuit as claimed in claim 10 wherein said control circuit triggering means includes a timing circuit that determines the alternate triggering of said first semiconductor switch and iS chosen to trigger the first semiconductor switch at some time during the first half of each half cycle of the AC supply voltage.

Claim 14

A supply circuit as claimed in claim 6 further comprising current rectifying means connected between the lamp electrodes and the combination heating and ignition circuit whereby the combination circuit is energized with a DC voltage but the lamp electrodes are heated with an AC current.

Claim 15

A supply circuit as claimed in claim 8 wherein said control circuit includes an RC timing circuit having a short time constant that determines the alternate triggering of said first semiconductor switch.