Ballast having a dimming device
AssigneePatent-Treuhand-Gesellschaft fur elektrische Gluhlamplen mbH
InventorsKlaus Fischer, Josef Kreittmayr
Life of this patent
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Abstract
A ballast having a dimming device for a low-pressure discharge lamp. For brightness control, the DC component of the periodically modulated envelope of the lamp current is varied. In this case, the current does not fall below predetermined minimum values for the lamp current. Phases with a high lamp current are characterized by a steep rising edge, compared with a flatter falling edge.
Claims12
An electronic ballast having a dimming device for the purpose of controlling the brightness of a low-pressure discharge lamp, designed for operation with periodically modulated lamp current, characterized in that, in order to control the lamp brightness, the dimming device is designed to adjust the lamp current as follows:
- with decreasing brightness, both the maxima and the minima of the envelope of the lamp current become smaller;
- with further decreasing brightness, the periodic modulation of the envelope of the lamp current is superimposed by a lower limit (MIN), optionally corresponding to zero, of the lamp current amplitude, resulting in periodic modulation of the envelope of the lamp current in lamp current pulse packets with lamp current amplitudes above the lower limit (MIN),
- with further decreasing brightness, the pulse packet widths decreasing and the intervals between the pulse packets with the limited lamp current amplitudes (MIN) increasing.
A method for controlling the brightness of a low-pressure discharge lamp by means of an electronic ballast having a dimming device, designed for operation with periodically modulated lamp current, characterized in that, in order to control the lamp brightness, the dimming device adjusts the lamp current as follows:
- with decreasing brightness, both the maxima and the minima of the envelope of the lamp current become smaller;
- with further decreasing brightness, the periodic modulation of the envelope of the lamp current is superimposed by a lower limit (MIN), optionally corresponding to zero, of the lamp current amplitude, resulting in periodic modulation of the envelope of the lamp current in lamp current pulse packets with lamp current amplitudes above the lower limit (MIN),
- with further decreasing brightness, the pulse packet widths decreasing and the intervals between the pulse packets with the limited lamp current amplitudes (MIN) increasing.
Dependencies are inferred from the claim text.