US 4,320,326 AGranted

Electronic device for controlling the brightness of an electric gas discharge lamp without an incandescent cathode

AssigneeElstrom Electronic AG

InventorsWalter Banziger, Hanspeter Coufal

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Abstract

For the purpose of controlling the electrical energy fed to an electrical gas-discharge lamp (20), without an incandescent cathode, as a function of a d.c. control voltage (U.sub.S), there is a circuit arrangement (IC1, R3-R11, C4-C6, D-1), by means of which the ignition timing or angle of a triac (TR1) may be varied within each alternating-voltage half-wave. In order to prevent the lamp (20) from being completely extinguished unintentionally, when adjusted to minimal brightness, an additional circuit arrangement (30, 42, R12-R20, C7, D3, T1) is provided, ensuring a given minimal intensity of the current, flowing through said lamp (20), regardless of the level of said d.c. control voltage (U.sub.S). Said additional circuit arrangement comprises a current transformer (30) and a rectifier arrangement (42) for producing a regulating voltage (U.sub.R) dependent upon the intensity of the lamp current which controls an electronically variable resistance (T1). The latter influences the critical voltage for the ignition-angle-control 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 and of mercury-vapor lamps or high-pressure sodium-vapor lamps used for interiors, highways and tunnels.

Claims13

Dependent claims

An electronic device for controlling the brightness of an electrical gas-discharge lamp, having no incandescent cathode, from an alternating-current network, by means of a circuit arrangement for controlling the electrical energy fed to the lamp by a triac arranged in the lamp supply circuit, the ignition angle of the said triac being adjustable, within each alternating-voltage half-wave, as a function of a d.c. control voltage, an additional circuit arrangement being provided for the production of a regulating voltage dependent upon the intensity of the current flowing through the gas-discharge lamp, for the purpose of ensuring automatically a given minimal current intensity flowing through the said lamp, regardless of the value of the said d.c. control voltage, the said additional circuit arrangement comprising a rectifier arrangement and a current transformer, of which the primary winding lies in the supply circuit to the gas-discharge lamp, while the secondary winding thereof is connected to the input of the said rectifier arrangement, the said regulating voltage being derived from the output of the said rectifier arrangement, characterized in that the additional circuit arrangement (30, 42, R12-R17, C7, D3, T1;

R21, R22, D4, T2) comprises a reference-voltage source (IC1, 35, 37) and a voltage divider (R15, R16, R17), the ends of which are connected to the terminals (44, 37), of opposite polarity of the output of the rectifier arrangement (42), on the one hand, and of the reference-voltage source (IC1, 35, 37) on the other hand, whereas the other output terminals (43, 35) of the said rectifier arrangement (42) and the reference-voltage source, respectively, are connected together;
and in that the regulating voltage (U.sub.R ;
U.sub.R1, U.sub.R2) is taken from a tap (45;
47) of the said voltage divider (R15, R16, R17;
R21, R22).

2 more elements

Dependencies are inferred from the claim text.