Ballast containing circuit for measuring increase in DC voltage component
AssigneeOsram Sylvania Inc.
InventorsJames N. Lester, William J. Roche
Life of this patent
Estimating the term…
Abstract
A ballast includes an inverter for providing an AC voltage to a discharge lamp. As the lamp approaches end-of-life a DC voltage component develops across the lamp. The ballast includes circuitry for monitoring the condition of each of the cathodes by measuring this DC voltage component. After a predetermined increase in this DC voltage component, the inverter is disabled in order to prevent excessive heating of the cathodes.
Claims12
A ballast for a discharge lamp having a pair of cathodes wherein said discharge lamp is characterized by a lamp voltage waveform having a DC voltage component when said lamp approaches end-of-life upon depletion of emissive material on one of said cathodes, said ballast comprising:
- an inverter for providing an AC voltage at a pair of output terminals;
- means for coupling said discharge lamp to said output terminals of said inverter;
- means for monitoring a condition of each of said cathodes by measuring said DC voltage component;
- and
- means for disabling said inverter after a predetermined increase in said DC voltage component whereby excessive heating of said one of said cathodes is prevented.
An arrangement comprising:
- a pair of AC input terminals adapted to receive an AC signal from an AC power supply;
- DC power supply means coupled to said AC input terminals for generating a DC supply voltage;
- inverter means coupled to said DC power supply means to receive said DC supply voltage and including a pair of semiconductor switches, means for driving said semiconductor switches, and a pair of output terminals;
- a discharge lamp coupled to said output terminals of said inverter means, said discharge lamp having a pair of cathodes and characterized by a lamp voltage waveform having a DC voltage component when said lamp approaches end-of-life upon depletion of emissive material on one of said cathodes;
- and
- means for disabling said inverter after a predetermined increase in said DC voltage component whereby excessive heating of said one of said cathodes is prevented.
Dependencies are inferred from the claim text.