Adaptive lamp warm up control for dimming ballast based on lamp impedance sensing
AssigneeUniversal Lighting Technologies, Inc.
InventorsWei Xiong, John J. Dernovsek, Candice Ungacta, Danny Pugh
Life of this patent
Estimating the term…
Abstract
A ballast is designed to adaptively warm-up one or more lamps driven by the ballast when the lamps are dimmed to a selected dimming level and lamp impedance instability results. The ballast can therefore maintain a stable light output in low ambient temperature conditions that normally cause lamp impedance instability and visible flickering of the lamp. The ballast uses lamp impedance sensing circuit to sense lamp instability and adaptively warms up the lamp whenever the ballast detects lamp instability by increasing the current provided to the lamp (i.e., current through the lamp) for a predetermined period of time.
Claims18
An electronic ballast comprising:
- an inverter functional to receive power from a power source and provide an alternating current (AC) signal at an inverter frequency;
- first and second output ballast output terminals;
- a resonant tank coupled to the inverter and configured to receive the AC signal from the inverter and provide an output signal across the first and second ballast output terminals;
- an impedance sensing circuit comprising
- a direct current (DC) power supply operable to provide a DC voltage referenced to a ballast ground,
- a first resistor connected between the DC power supply and the first ballast output terminal,
- a second resistor having a first terminal connected to the first ballast output terminal and a second terminal,
- a third resistor connected between the ballast ground and the second terminal of the second resistor;
- and
- a controller connected to the inverter and the second terminal of the second resistor, wherein the controller is effective to
- sense a lamp impedance of a lamp coupled to the ballast output terminals by detecting a DC voltage impedance signal provided at the second terminal of the second resistor,
- calculate a change in the lamp impedance over time,
- determine whether the lamp impedance is unstable by determining whether the change in the lamp impedance over time exceeds a predetermined threshold, and
- increase a current provided to the lamp by the ballast for a predetermined period of time when the lamp impedance is unstable by adjusting the inverter frequency.
A light fixture comprising:
- a ballast having first and second ballast output terminals;
- a lamp connected between the first and second ballast output terminals;
- the ballast further comprising
- an inverter operable to receive power from the power source and provide an alternating current (AC) signal at an inverter frequency,
- a resonant tank coupled to the inverter and configured to receive the AC signal from the inverter and provide a ballast output signal across the first and second ballast output terminals,
- an impedance sensing circuit comprising
- a direct current (DC) power supply operable to provide a DC voltage referenced to a ballast ground,
- a first resistor connected between the DC power supply and the first ballast output terminal,
- a second resistor having a first terminal and a second terminal, wherein the first terminal of the second resistor is connected to the first ballast output terminal, and
- a third resistor connected between the ballast ground and the second terminal of the second resistor;
- and
- a controller connected to the inverter and the second terminal of the second resistor operable to:
- sense the lamp impedance via the impedance signal provided at the second terminal of the second resistor;
- calculate a change in the lamp impedance over time;
- determine whether the lamp impedance is unstable by determining whether the change in the lamp impedance over time exceeds a predetermined threshold;
- and
- increase the current provided to the lamp for a predetermined period of time when the lamp impedance is unstable by adjusting a frequency of the AC signal provided by the inverter;
- and
- a housing connected to the lamp and the ballast.
Dependencies are inferred from the claim text.