Add-on instant restrike device for an hid lamp

Claim 1

In combination with a ballast for a high-intensity discharge lamp having two input terminals and two electrodes operatively disposed within the lamp, said ballast including a constant output voltage transformer having transformer input terminals and transformer output terminals, said transformer input terminals adapted to be connected to an AC power source, and a ballasting capacitor means having one terminal connected to one of said transformer output terminals and the other terminal of said ballasting capacitor means and the other of said transformer output terminals constituting the normal ballast output terminals across which the terminals of said high-intensity discharge lamp are normally adapted to be connected, the improvement which comprises an add-on instant restrike device for initiating an operating discharge in said lamp when it is still hot from previous operation, said restrike device comprising: (a) high-voltage pulse-generating means connected across said normal ballast output terminals, said pulse-generating means comprising autotransformer means having a tap defining the primary and secondary thereof and said autotransformer means connected at its end portions in circuit between said other ballasting capacitor means terminal and one of said lamp input terminals, storage capacitor means connected in circuit across said normal ballast output terminals, gate-controlled solid-state switching means connected between said tap of said autotransformer means and said storage capacitor means to form a series loop comprising the primary of said autotransformer means and said storage capacitor means and said switching means, and first voltage responsive conduction means connected in circuit across said storage capacitor means and having an output connected to gate means of said solid-state switching means, and when said pulse-generating means is energized said storage capacitor means has applied thereacross an increasing potential which causes said first voltage responsive conduction means to conduct when a predetermined value of voltage is applied across said storage capacitor means which gates said switching means to discharge said storage capacitor means through said series loop to generate a short duration high-voltage pulse across said autotransformer means and create through said high-intensity discharge lamp an ionized discharged path; (b) intermediate voltage generating means which coacts with said ballasting capacitor means to charge said ballasting capacitor means to an intermediate voltage through a plurality of half cycles of energizing potential when said ballast is energized, said intermediate voltage generating means comprising charging means including a charging capacitor means having one terminal thereof in circuit with said one transformer output terminal and the other terminal thereof connected to said other transformer output terminal, second voltage responsive conduction means having an anode and a cathode, said anode of said second voltage responsive conduction means connecting to said one transformer output terminal and said cathode of said second voltage responsive conduction means connecting to said one terminal of said charging capacitor means, whereby when said ballast is energized while said lamp is still hot, said storage capacitor means charges while said ballasting capacitor means simultaneously charges to an intermediate voltage, and when said storage capacitor means is discharged through said loop, there is created through said lamp an ionized discharge path which permits said ballasting capacitor means to discharge through said lamp and form an operating hot spot on one of said lamp electrodes which is adequate to permit sustained operation of said lamp thereafter.