When multiple cold cathode fluorescent lamps (CCFLs) are set up in a backlight module, parasitic capacitances are inevitably existent between the lamps and the aluminum back-plank. These parasitic capacitances are different from each other in introducing different leakage currents, and in turn cause current imbalance between lamps with undesired unequal brightness of the backlight module. In order to tackle this current imbalance problem, it relies critically upon a balance driving scheme.
This thesis adopts the impedance-matching principle for a uniform light output. A detailed analysis and design of the balance circuit is implemented in a direct-type backlight module, which employs a series resonant parallel-loaded inverter with a transformer to generate a high AC voltage to drive multiple lamps. Adding appropriate capacitors on the load resonant circuits helps alleviate the discrepancy among lamp currents. Based on the experimental results, the maximum total current deviation is defined as an index of the current imbalance for multiple lamps system. Accordingly, the minimum impedance ratio can be provided for the designers to achieve balance driving.
A prototype of the multi-lamp driving circuit with balance capacitors is designed and built for a backlight module with 16 lamps in a 32-inch liquid crystal display (LCD). Simulation and experimental results demonstrate the effectiveness and feasibility of the current balance scheme.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0712106-010919 |
| Date | 12 July 2006 |
| Creators | Lin, Jia-Chang |
| Contributors | J. Y. Lee, S. H. Yu, L. L. Lee, C. S. Moo, H. C. Yen |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0712106-010919 |
| Rights | withheld, Copyright information available at source archive |
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