Protection for external electrode fluorescent lamp system
AssigneeO2 Micro, Inc.
InventorsYung-Lin Lin, Da Liu
Life of this patent
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Abstract
The present invention provides a driving circuit with protection function for driving a set of external electrode fluorescent lamps (EEFL). The drive circuit includes a transformer connected to the set of EEFLs, a switching network connected to the transformer which delivers power to the transformer, a sensing circuit connected to the set of EEFLs which detects disconnection if one light source is disconnected, and a controller connected to the switching network which controls the switching network to reduce the total current supplied to the EEFLs which remain connected, if the sensing circuit detects that one EEFL is disconnected. Appropriate protection can therefore be implemented when the EEFL is disconnected on one end or both ends.
Claims33
A cold cathode fluorescent lamp driving circuit with protection
- function for driving a plurality of cold cathode fluorescent lamps comprising:
- a first transformer coupled to said plurality of cold cathode fluorescent lamps;
- a switching network coupled to said first transformer which delivers power to said first transformer;
- a sensing circuit coupled to said plurality of cold cathode fluorescent lamps which detects disconnection if one cold cathode fluorescent lamp is disconnected, wherein said sensing circuit comprises a first end sensing circuit for detecting disconnection if said one cold cathode fluorescent lamp is disconnected on one end, and wherein said first end sensing circuit comprises a first sensing resistance and a second sensing resistance, wherein said first end sensing circuit senses a first voltage on said first sensing resistance and a second voltage on said second sensing resistance and detects disconnection if a sum of said first voltage and said second voltage exceeds a first predetermined level;
- and
- a controller coupled to said switching network which controls said switching network to reduce the total current supplied to the cold cathode fluorescent lamps which remain connected if said sensing circuit detects that said one cold cathode fluorescent lamp is disconnected.
A method for protecting a plurality of cold cathode fluorescent lamps from being overdriven comprising:
- detecting if one cold cathode fluorescent lamp is disconnected;
- generating a sensing signal indicating whether said one cold cathode fluorescent lamp is disconnected;
- reducing a total current supplied to the plurality of cold cathode fluorescent lamps which remain connected if said sensing signal indicates that said one cold cathode fluorescent lamp is disconnected;
- and
- sensing a first voltage and a second voltage and calculating a sum of said first voltage and said second voltage.
Dependencies are inferred from the claim text.