A starter circuit for a discharge lamp having preheated electrodes

Claim 2

A starter circuit for a discharge tube having preheated electrodes comprising, a pair of input terminals adapted for connection to a sinusoidal source of AC voltage, an inductance, means serially connecting said inductance and said discharge tube across said input terminals, a semiconductor controlled rectifier connected directly in shunt with the tube and in series with the tube electrodes, a control circuit coupled to the control electrode of the controlled rectifier and including means for delaying the start of conduction therein for a time period between 1/12 theta and 3/8 theta seconds after a zero crossing of the AC supply voltage, wherein theta is the frequency in cycles per second of the AC supply voltage, a capacitor and an impedance element serially connected in shunt with the tube, the capacitance of said capacitor being chosen so that the impedance thereof lies between 40 times and 150 times the operating impedance of the tube, the total impedance of the last-mentioned series arrangement being determined mainly by the capacitor.

Claim 3

A starter circuit as claimed in claim 1 wherein said impedance element is a resistor and the series arrangement of the capacitor and resistor is connected to the ends of the tube electrodes that are remote from the input terminals.

Claim 4

A starter circuit as claimed in claim 1 wherein the control circuit is connected in Shunt with the tube so that the control circuit is responsive to the decrease in voltage across the tube subsequent to ignition thereof to hold the control electrode of the controlled rectifier at a voltage level below the rectifier firing voltage.

Claim 5

A starter circuit as claimed in claim 3 wherein said control circuit comprises, a resistor and capacitor connected in series across the tube, and a voltage breakdown element connected between the capacitor and the control electrode of the controlled rectifier.

Claim 6

A starter circuit for the discharge tube having a pair of preheated electrodes comprising, first and second input terminals adapted for connection to a sinusoidal source of AC voltage, an inductance connected between the first input terminal and one terminal of a first one of the tube electrodes, means connecting the second input terminal to a first terminal of the second tube electrode, a resistor and a capacitor connected in series between a second terminal of the first electrode and a second terminal of the second electrode, a semiconductor controlled rectifier connected between said second terminals of the first and second electrodes, and a control circuit having first and second input terminals connected between said second terminals of the first and second electrodes and an output terminal connected to the control electrode of the controlled rectifier, said control circuit including means for delaying ignition of the controlled rectifier to a firing angle lying between 30* and 135* after a zero crossing of the AC supply voltage, the capacitance of said capacitor being chosen so that the impedance thereof lies between 40 times and 150 times the operating impedance of the tube, and the impedance of the capacitor being approximately 95 percent of the total impedance of the series arrangement of the resistor and the capacitor.

Claim 7

A starter circuit for the discharge tube having a pair of preheated electrodes comprising, first and second input terminals adapted for connection to a sinusoidal source of AC voltage, an inductance connected between the first input terminal and one terminal of a first one of the tube electrodes, means connecting the second input terminal to a first terminal of the second tube electrode, a resistor and a capacitor connected in series between a second terminal of the first electrode and a second terminal of the second electrode, a semiconductor controlled rectifier connected between said second terminals of the first and second electrodes, and a control circuit having first and second input terminals connected between said second terminals of the first and second electrodes and an output terminal connected to the control electrode of the controlled rectifier, said control circuit including means for delaying ignition of the controlled rectifier to a firing angle lying between 30* and 135* after a zero crossing of the AC supply voltage, the capacitance of said capacitor being chosen so that the impedance thereof lies between 40 times and 150 times the operating impedance of the tube, and the impedance of the capacitor being approximately 95 percent of the total impedance of the series arrangement of the resistor and the capacitor.