| 摘要 |
<p>For the purpose of controlling the electrical energy fed to an electrical gas discharge lamp, without an incandescent cathode, as a function of a d.c. control voltage, there is provided a circuit arrangement by means of which the ignition timing or angle of a triac may be varied within each alternating-voltage half-wave. In order to prevent the lamp from unwanted extinction when adjusted to minimal brightness, an additional circuit arrangement is provided, ensuring a given minimal intensity of the current flowing through the said lamp, regardless of the level of the said d.c. control voltage. The additional circuit arrangement comprises a current transformer and a rectifier arrangement for producing a regulating voltage depending upon the intensity of the lamp current and controlling an electronically variable resistance. The latter influences the critical ignition-angle-control voltage whenever the intensity of the lamp current drops below a permissible minimal value, in such a manner that any further decrease in current intensity is automatically counteracted. The device is intended, for example, for controlling the brightness of lighting units, comprising mercury-vapour lamps or high-pressure sodium-vapour lamps, used for interiors,highways and tunnels.</p> |
