Browsing by Author "Ersoy, Melisa"
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Master ThesisPublication Metadata only Current balancing circuit design for parallel LED strings in dual-transformer LLC resonant topologyErsoy, Melisa; Poyrazoğlu, Göktürk; Poyrazoğlu, Göktürk; Tekin, A.; Barkana, D. E.; Department of Electrical and Electronics EngineeringNew display technologies require small form factor designs with more backlight power. When multiple transformers drive parallel-connected LED strings, the difference in transformer leakage inductance and LED string voltage creates a backlight current imbalance. This current imbalance causes the following problems, - The low-voltage string draws more current. - High current causes hot spots on the backlight and a shorter lifespan. This issue is seen as an unevenly distributed backlight on the customer side. In this study, a cost-efficient balancing circuit for eight parallel-connected LED strings is simulated and developed utilizing two transformers in the half-bridge LLC resonant topology while providing the power in a comparatively slim design. The current imbalance for the 145W backlight power was 57.58% when there was an 8% change in leakage inductance between the transformers and a 10% change in LED string voltages. When the back cover was removed, the difference in temperature between the LED strings was recorded at room temperature as 31.8℃. The current imbalance between the LED strings is decreased to 9.99% when the current balancing components are connected to the circuit. When there is no difference between the LED string voltages, the maximum current imbalance is 2.59%. The cost of the proposed method is almost three times less than the conventional method, and for the same backlight power, it is 5.6% more efficient.Conference ObjectPublication Metadata only Current balancing circuit design for parallel LED strings in QDOT high bright TV with dual-transformer LLC resonant topology(IEEE, 2022) Ersoy, Melisa; Poyrazoğlu, Göktürk; Electrical & Electronics Engineering; POYRAZOĞLU, Göktürk; Ersoy, MelisaNew LED technologies demand slim designs with increased backlight power. When the parallel-connected LED strings are driven by multiple transformers, the magnetic coupling difference and the LED string voltage difference cause backlight current mismatch problem. This imbalance causes the line with low voltage to draw more current hence to create heat spots on the backlight causing reduced lifetime. This problem is observed as backlight fluctuation at the end-user side. In this study, a cost-effective balancing circuit is simulated and implemented for eight parallel-connected LED strings using two transformers in an LLC half-bridge resonant topology while meeting the power demand in a relatively slim design. For the 145W backlight power, the current mismatch was 57.59% when there was an 8% deviation in transformer leakage inductance and a 10% variation between LED string voltages. The temperature difference between the strings was measured as 31. 8°C taken at room temperature with the open back cover. With the balancing circuit, the LED current difference being reduced to 9.99%. When the string voltages are the same, the maximum deviation in the current is measured as 2.59%.