Ballast unit for gas discharge lamps

Claim 2

A ballast unit for gas discharge lamps having a pair of electrodes, comprising: a choke means, exclusively for limiting the current to the lamp after lamp firing, connected in series with the lamp electrodes; at least one semiconductor switching means, having a control electrode, for brief preheating of the filaments of the lamp at increased rated current, said switching means being connected in parallel with said lamp electrodes; and a control circuit means operating in response to an AC voltage supplied to said lamp electrodes and also connected to said control electrode for initially triggering said semiconductor means for a predetermined switch-on time during each half cycle of said AC voltage, to heat the filaments of the lamp with an effective current greater than normal rated current, as well as reducing the switch-on time during each half cycle until the lamp fires, and further increasing voltage peaks across the lamp for a predetermined preheating period prior to reaching ignition voltage, thereby avoiding cold-starting of the lamp; said control circuit means including: a storage device capable of storing a charge corresponding to the voltage applied to the lamp; a discharge resistor connected to said charge storage device; and overvoltage peak means to cut off any overvoltage peaks.

Claim 3

The ballast unit of claim 1 wherein said control circuit connected to said semiconduCtor switching means and said lamp electrodes including a limiting resistor connected to one of said lamp electrodes; a bridge rectifier having an R-C component connected between said limiting resistor and the other of said lamp electrodes; a time element including a capacitor and a resistor in parallel connected across said bridge rectifier; and control voltage means connected to said bridge rectifier and said limiting resistor including a series resistor, a control diode connected in series with said resistor, and a control capacitor connecting the junction of said series resistor and said control diode with said one of said lamp electrodes; and having the following control states a. switch-on phase with fully triggered control-voltage-independent semiconductor switch; b. starting phase with partly triggered lamp-firing-voltage-dependent semiconductor switch; c. protection phase with fault-dependent semiconductor switch; wherein said control circuit concurrently forms a short circuit for increased voltages across the gas discharge path so long as the starting phase has not begun, with said limiting resistor forming the load resistor for said time element and concurrently forming an early firing protection for the tube, said R-C component of said bridge rectifier transfering the limiting voltage to the lamp; and, in conjunction with said control voltage means, concurrently triggers said semiconductor switching means.

Claim 4

The ballast unit of claim 2 wherein the charging rate of said time element and the behavior of said limiting resistor correspond to the heat-up rate of said electrodes and the cool-down time of said electrodes coincides with the discharge time constant of said time element for the purpose of skipping part or all of the switch-on and starting process in the case of a short firing pause.

Claim 5

The ballast unit of claim 1 further comprising a capacitor means connected in series to said semiconductor switching means for reducing the apparent resistance of said choke by acting in opposition thereto only when said semiconductor means is triggered, a trigger diode connected to said semiconductor switching means; and voltage divider means for fully activating said semiconductor switching means and then, until the beginning of lamp starting, partly activating said semiconductor switching means.

Claim 6

The ballast unit of claim 1 comprising means for controlling said semiconductor switching means in such a manner that a d.c. component increased above the shortcircuit current arises for said lamp electrode, and for preventing early starting of the lamp; wherein said increased current arises only until the starting of the lamp.

Claim 7

The ballast unit of claim 1 including a capacitor connected in series with said choke means and in parallel with the lamp, said choke means being tuned substantially to the third harmonic of the mains frequency.

Claim 8

The ballast unit of claim 6 comprising a saturation choke connected in parallel with the gas discharge lamp.

Claim 9

The ballast unit of claim 7 comprising a positive-temperature resistor connected in series with said saturation choke.

Claim 10

The ballast unit of claim 7 comprising a thermal cut-out connected in series with the parallel combination of said lamp and said capacitor.

Claim 11

The ballast unit of claim 7 comprising triggering means having a predetermined time constant connected in parallel with the gas discharge lamp and said saturation choke for triggering said semiconductor switching means and for supplying thereto a cut-off voltage after the starting of the gas discharge lamp for preventing voltage overload of said semiconductor switching means.

Claim 12

The ballast unit of claim 10 comprising d.c. voltage circuit means for developing an additional cut-off voltage for preventing voltage overload of said semiconductor switching means, said d.c. voltage circuit means having a greater time constant than that of said triggering means.

Claim 13

The ballast unit of claim 6 wherein said choke includes a heater winding means for the additional preheating of the electrodes.

Claim 14

The ballast unit of claim 12 wherein said control circuit comprises a resistor, and a capacitive apparent resistance circuit connected in parallel with said resistor; wherein said semiconductor switching means is a triac.

Claim 15

The ballast unit of claim 12 comprising a capacitor connected in parallel with said semiconductor switching means, said semiconductor switching means having a control electrode, for cold-starting protection, a diode and a resistor bridging said semiconductor switching means, and a cut-off circuit and a safety cut-off circuit both connected to said control electrode of said semiconductor switching means.

Claim 16

The ballast unit of claim 12 comprising a differentiator and rectifier means connected to said semiconductor switching means for cutting off said semiconductor switching means.

Claim 17

A ballast unit according to claim 1, wherein: said storage device compensates at least in part for the resistance of said choke means, said storage device operating exclusively in said control circuit during the heating of said filaments of the lamp and being inoperative after the lamp fires.

Claim 18

A ballast unit according to claim 1, wherein the apparent resistance of said storage device is approximately 2 - 3 times smaller than said ballast choke means.

Claim 19

A ballast unit according to claim 1, wherein said control circuit means further includes a heater circuit; said heater circuit being asymmetrically loaded only until the lamp fires; said heater circuit including a diode and a VDR connected in parallel, the parallel combination being connected in series with one of the pair of lamp electrodes and with said at least one semiconductor switching means; and a damping resistor and damping capacitor connected in series with each other and said VDR, and in parallel with said semiconductor switching means, whereby an increased direct current component in excess of short circuit current is produced in said heater circuit.

Claim 20

A ballast unit according to claim 1, wherein said control circuit means further includes a heating circuit; said heating circuit being asymmetrically loaded only until the lamp fires; a storage capacitor connected through a storage capacitor resistor to said control electrode and being chargeable by the lamp voltage; a further resistor connecting one of said pair of lamp electrodes to said control electrode; a charging current diode electrically connected to one of said pair of lamp electrodes and to said storage capacitor; said heating circuit being connected to the lamp such that the cut-off voltage component of said storage capacitor counteracts the cut-off voltage component of the lamp voltage, and the time constant of said storage capacitor being such that the filament of the lamp reaches a glowing state prior to the charge on said storage capacitor reaching maximum value.

Claim 21

The ballast unit according to claim 1 further comprising an auxiliary winding including a primary and secondary winding serially interconnected in the parallel path of said semiconductor means and said lamp electrodes, said choke means and said auxiliary winding being wound to a same iron core in opposite winding directions, said auxiliary winding having the same number of windings as said choke means.

Claim 22

The ballast unit of claim 20, further comprising a primary firing circuit connected to said primary auxiliary winding having capacitor means for providing the triggering energy, converting the ballast unit into a wattless-current-compensated ballast unit, providing an overvoltage peak protection for said semiconductor switching means and developing the lamp firing voltage in said secondary auxiliary winding; wherein said semiconductor switching means closes said heating circuit and said primary firing circuit.