TEMPERATURE CONTROLLED GAS DISCHARGE DEVICE

摘要

1454732 Supply systems for gas discharge lamps PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 29 April 1975 [2 May 1974] 17746/75 Heading H2H Apparatus comprising a gas discharge tube is provided with a heating element which extends substantially throughout the length of the tube, the element being controlled so as to determine the operating temperature of the tube whereby the use of a ballast device is unnecessary. A sodium vapour discharge tube 10 is provided with electrodes 9, 12 and a transparent electrically conducting layer 15 extending along the length of the tube, electrical connection to the layer 15 being made by sleeves 22, 23. The tube 10 is supplied from an A.C. source 1, 2 by way of a bridge rectifier 3 and a main circuit which includes a diode 6, the operating coil 20 of a reedswitch 16, a diode 8 and the electrodes 9, 12, the circuit being connected across the D.C. terminals of the bridge 3. A second auxiliary circuit is also connected across the bridge 3 and includes the collector-emitter path of a transistor 17, sleeve 22, layer 15 and sleeve 23. After the tube 10 has been ignited by the application of a suitable potential to terminals 24, 25 and a small current flows in the main circuit, such current in the coil 20 being insufficient to cause operation of the reed relay 16, the movable centre contact thereof remains in the 'down' position, as shown, whereby transistor 17 is rendered conductive to enable current to flow through the layer 15 to heat the tube 10. Should the tube become overheated the current in the main circuit will increase so causing operation of the reed switch 16 to the 'up' position. The transistor 17 becomes non-conductive to prevent current flow in the layer 15 whereupon the tube 10 cools down and the tube temperature is maintained at a desired operating value by the ON-OFF action of the layer 15. With the reed switch 16 in the 'up' position a circuit exists from the point 5 to the diode 8 by way of the centre and upper contacts of the switch 16 and the portion of the coil 20 selected by the slider 21. This circuit reduces the hysteresis of the reed switch 16. In a second embodiment the heating of the tube 10 is effected by a helical coil wound around the tube.