Apparatus for driving a gas discharge lamp

Abstract

A driver (10) for driving a gas discharge lamp (L) comprises a current generator (1; 2) for generating a lamp current with a main lamp current component and, for arc-straightening purposes, a ripple current component. A controller (3) controls the current generator such as to set the ripple frequency (fR) and ripple amplitude (M). A memory (5) contains data defining a set point (SP) for the ripple frequency and ripple amplitude. A measuring device (4) provides at least one measuring signal indicative of arc curvature and arc stability. The controller is capable of operating in a ripple optimizationmode in which the controller makes small adjustments to the ripplefrequencyand ripple amplitude to find improved arc-straightening, and, if such improvement is found, controls the current generator on the basis of the adjusted set pointor otherwise resumes operation on the basis of the original set point (SP) in the memory (5).

Description

technical field [0001] This invention relates generally to gas discharge lamps and more particularly to high pressure or high intensity discharge lamps. Background technique [0002] When gas-discharge lamps are operated in a horizontal position, it is well known that problems arise, such as the possible curved shape of the electric arc (arc), notably due to gravitational forces or convection currents; it is also known that the application of high-frequency current components may cause the arc to straighten ( straightening); see for example US-5436533 and EP-0713352. For some lamp types it is beneficial if this high frequency is swept. [0003] The problem is that the exact frequency at which arc straightening is achieved is different for different lamp types, and this frequency is not even necessarily the same for different lamps of the same type, e.g. due to production tolerances, differences in lamp orientation, aging, etc. . In addition, there is another problem that ...

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Problems solved by technology

[0003] The problem is that the exact frequency at which arc straightening is achieved is different for different lamp types, and this frequency is not even necessarily the same for different lamps of the same type, e.g. due to production tolerances, differences in lamp orientation, aging, etc.

In addition, there is another problem that high-frequency current components may produce acoustic resonance, which is undesirable because acoustic resonance may cause light flicker, arc distortion, or even arc tube failure, etc.

Another complicating factor is that the exact resonant frequency varies for different lamp types, and even for different lamps of the same type

It is then problematic to design a lamp driver that is suitable for the addition of a high frequency current ripple such that in all cases the current ripple frequency is beneficial in terms of arc straightening and not detrimental in terms of resonance.

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