Arrangement for igniting and supplying a discharge lamp

Claim 2

An ignition circuit for a discharge lamp having preheatable electrodes comprising, a pair of input terminals adapted to be connected to a low frequency alternating voltage supply source, means connecting a stabilizing inductor in series with the lamp across said input terminals, a starter circuit for the lamp electrodes including means connecting the ends of the lamp electrodes remote from the input terminals together via a transistor switch, a control circuit coupled to the input terminals and connected to the base of the transistor and including means for closing the transistor switch during a first part of the ignition procedure of the lamp and which opens said transistor switch in the operation condition of the lamp, said control circuit including a branch circuit which is energized at least during the last part of the ignition procedure of the lamp, said branch circuit having timing circuit means with a short time constant relative to the period of the alternating supply voltage so that the transistor is rendered conducting and non-conducting at least several times during a half cycle of the alternating voltage.

Claim 3

An ignition circuit as claimed in claim 1, wherein the control circuit includes a breakdown element and the timing circuit means includes a series arrangement of a first resistor and a first capacitor, means connecting the breakdown element between the transistor base and a point between the first resistor and the first capacitor, means connecting said series arrangement in shunt with the transistor switch, a second resistor connected in shunt across the combination of at least the breakdown element and the first capacitor and the connection between the lamp and the first capacitor including a diode whose pass direction corresponds to that of the transistor.

Claim 4

An ignition circuit as claimed in claim 1, characterized in that the time constant of the timing circuit means of the control circuit is so short that during the last part of the ignition procedure of the lamp the quotient of the frequency of the current flowing through the transistor and the frequency of the alternating voltage is between 10 and 10,000.

Claim 5

An ignition circuit as claimed in claim 2, characterized in that the breakdown voltage of the breakdown element is between the effective value of the voltage of the alternating voltage source and the operating voltage of the lamp.

Claim 6

An ignition circuit as claimed in claim 1 wherein the starter circuit further comprises a second transistor having a base electrode connected to a branch of a second timing circuit whose time constant is longer than the time constant of the first timing circuit means, said second timing circuit being connected to control the conducting state of the second transistor, means connecting the branch of the second timing circuit in parallel with the branch of the first timing circuit, means connecting the main electrode circuit of the second transistor to the first timing circuit so that a change in conduction of the second transistor applies a control voltage to the base of the first transistor to bring the first transistor into its cut-off state.

Claim 7

An ignition circuit as claimed in claim 1 wherein the starter circuit is provided with a rectifier bridge whose input terminals are connected to the ends of the lamp electrodes remote from the input terminals, and means connecting the main electrodes of the first transistor to the output terminals of said rectifier bridge.

Claim 8

An ignition circuit as claimed in claim 5 wherein said first timing circuit means includes a series arrangement of a first resistor and a first capacitor and said main electrode circuit connecting means connects the second transistor in shunt with the first capacitor.

Claim 9

An ignition circuit as claimed in claim 5, wherein the first timing circuit means includes a series arrangement of a first resistor and a first capacitor and a breakdown element connected between the first transistor base and the junction between the first resistor and the first capacitor, means connecting said series arrangement in shunt with the transistor switch, a second resistor connected in shunt across the combination of the breakdown element and the first capacitor, and the branch of the second timing circuit includes a series arrangement of a third resistor and a second capacitor, and means connecting the base of the second transistor through a fourth resistor to the junction between the third resistor and the second capacitor.

Claim 10

An ignition circuit as claimed in claiim 8, characterized in that the second capacitor is shunted by a fifth resistor.

Claim 11

An ignition circuit as claimed in claim 1 wherein the first timing circuit means includes a series arrangement of a first resistor and a first capacitor connected in shunt with the transistor switch and a breakdown element connected between the base of the transistor switch and the junction between the first resistor and the first capacitor, and the first capacitor is shunted by a second resistor having a large negative temperature coefficient chosen so that before the lamp is ignited, the voltage across the first capacitor is lower than the threshold voltage of the breakdown element.

Claim 12

An ignition circuit as claimed in claim 1 wherein the first timing circuit means includes a series arrangement of a first resistor and a first capacitor connected in shunt with the transistor switch and a breakdown element connected between the base of the transistor switch and the junction between the first resistor and the first capacitor, and further comprising a further transistor connected in series with the series arrangement of the first resistor and its first capacitor in shunt with the main electrode circuit of the transistor switch, means connecting the base of said further transistor to a second timing circuit whose time constant is substantially longer than the time constant of the first timing circuit means so that the further transistor is triggered into conduction after a delay of at least one period of the alternating supply voltage.

Claim 13

An ignition circuit as claimed in claim 11, characterized in that the first capacitor is shunted by a further resistor having a negative temperature coefficient.

Claim 14

An ignition circuit as claimed in claim 11, further cmprising a control circuit for the further transistor including a series arrangement of a diode, a second resistor and a second capacitor, and means connecting one end of said series arrangement to a point between one of the input terminals and the stabilizing inductor.

Claim 15

An ignition circuit as claimed in claim 1 wherein the first timing circuit means includes a series arrangement of a first resistor and a first capacitor connected in shunt across the transistor switch and a breakdown elemenT connected between the control electrode of the transistor switch and the junction between the first resistor and the first capacitor, and said starter circuit further comprises a diode bridge with input terminals connected to respective lamp electrodes and output terminals to which the transistor switch is connected.

Claim 16

A supply circuit for an electric discharge lamp having first and second preheatable electrodes comprising, a pair of input terminals for applying a low frequency AC voltage to the supply circuit, a ballast impedance, a controlled semiconductor switch, means connecting the ballast impedance and the semiconductor switch in series circuit with said first and second lamp electrodes across the input terminals to form a heating circuit for the electrodes, a control circuit coupled to the input terminals and having an output terminal connected to a control electrode of said semiconductor switch to control the conductive state thereof, said control circuit including a first timing circuit for applying a time varying switching voltage to said output terminal, the time constant of said first timing circuit being substantially shorter than a half period of the AC voltage whereby the switching voltage turns the semiconductor switch on and off a plurality of times during a half cycle of the AC voltage, said control circuit further comprising means responsive to the application of an AC voltage to said input terminals for holding the semiconductor switch in the cut-off state via said output terminal and commencing at a given time subsequent to the application of AC voltage to the input terminals, which given time is sufficient to allow the ignition of the discharge lamp.

Claim 17

A supply circuit for an electric discharge lamp having first and second preheatable electrodes comprising, a pair of input terminals for applying a low frequency AC voltage to the supply circuit, a ballast impedance, a controlled semiconductor switch, means connecting the ballast impedance and the semiconductor switch in series circuit with said first and second lamp electrodes across the input terminals to form a heating circuit for the electrodes, a control circuit coupled to the input terminals and having an output terminal connected to a control electrode of said semiconductor switch to control the conductive state thereof, said control circuit including a first timing circuit for applying a time varying switching voltage to said output terminal, the time constant of said first timing circuit being substantially shorter than a half period of the AC voltage whereby the switching voltage turns the semiconductor switch on and off a plurality of times during a half cycle of the AC voltage, said control circuit further comprising means responsive to the application of an AC voltage to said input terminals for holding the semiconductor switch in the cut-off state via said output terminal and commencing at a given time subsequent to the application of AC voltage to the input terminals, which given time is sufficient to allow the ignition of the discharge lamp.

Claim 18

A supply circuit as claimed in claim 15 further comprising a full wave rectifier circuit connected between the lamp electrodes and the semiconductor switch so that an AC heating circuit flows through the lamp electrodes when the semiconductor switch is closed during the ignition period, said rectifier circuit being connected to supply DC operating voltages to at least a part of the control circuit and to the semiconductor switch.

Claim 19

A supply circuit as claimed in claim 15 wherein said first timing circuit includes a capacitor, said supply circuit further comprising, a voltage breakdown element coupling said first timing circuit to the control electrode of said semiconductor switch, and a discharge circuit for the capacitor that includes said breakdown element.

Claim 20

A supply circuit as claimed in claim 15 wherein said holding means of the control circuit further comprises, a second controlled semiconductor switch coupled to the control electrode of the first semiconductor switch to prevent conduction thereof when the second semiconductor switch is triggered into conduction, and a second timing circuit coupled to the control electrode of the second semiconductor switch to apply thereto a time varying switching voltage, said second timing circuit having a longer time constant than the first timing circuit so that the second semiconductor switch is triggered into conduction several cycles of the AC voltage subsequent to the first conduction period of the first semiconductor switch during an ignition cycle.

Claim 21

A supply circuit as claimed in claim 18 wherein said first timing circuit includes a capacitor coupled to the control electrode of the first semiconductor switch via a voltage breakdown element, and said second semiconductor switch is connected in shunt with said capacitor to limit the capacitor voltage during the conduction period of the second semiconductor switch.

Claim 22

A supply circuit as claimed in claim 15 wherein said first timing circuit includes an RC circuit with a capacitor coupled to the control electrode of the first semiconductor switch via a switching device controlled by the capacitor voltage, and said holding means includes a negative temperature coefficient resistor connected in shunt with the capacitor and chosen so that after a giVen heating period its resistance attains a value to limit the capacitor voltage to a value below the switching voltage of said switching device.

Claim 23

A supply circuit as claimed in claim 15 wherein said first timing circuit includes an RC circuit with a capacitor coupled to the control electrode of the first semiconductor switch via a switching device controlled by the capacitor voltage and a positive temperature coefficient resistor connected in series with the capacitor.

Claim 24

A supply circuit as claimed in claim 15 wherein said first timing circuit includes an RC circuit with a capacitor coupled to the control electrode of the semiconductor and switch via a switching device, said holding means comprises, a transistor connected in series with said RC circuit, a second timing circuit coupled to the control electrode of the transistor to apply thereto a time varying switching voltage, said second timing circuit having a longer time constant than the first timing circuit, the transistor being triggered into conduction at a time subsequent to that of the semiconductor switch which time is sufficient to heat the electrodes and ignite the lamp.

Claim 25

A supply circuit as claimed in claim 22 further comprising a negative temperature coefficient resistor connected in parallel with the timing capacitor.

Claim 26

A supply circuit as claimed in claim 22 wherein said second timing circuit comprises a diode, a resistor and a second capacitor connected in series circuit across the input terminals.

Claim 27

A supply circuit as claimed in claim 15 wherein said control circuit is connected so as to energize and operate said first timing circuit during both half cycles of the AC voltage thereby to switch said semiconductor switch independently of the polarity of the AC voltage, and wherein the time constant of the first timing circuit is chosen so as to trigger the semiconductor switch at a frequqency between 10 and 10,000 times the frequency of the AC voltage.

Claim 28

A supply circuit as claimed in claim 15 wherein the time constant of the first timing circuit is chosen so as to trigger the semiconductor switch at frequency between 20 and 2000 times the frequency of the AC voltage.