The trend in Plasma Display Panel (PDP) TV is towards the thinner thickness, lighter weight, and fan-less system. For achieve this goal, it is desired advanced power conversion technique to implement a low-profile power supply for PDP. As PDP power module, LLC resonant converter is widely used because it can achieve both high efficiency and reliability. To achieve a low-profile circuit configuration, it is necessary to operate the converter at high switching frequency. LLC resonant converter can be operated at high switching frequency because of softswitching operations. However, it is a problem that the temperature of flat transformer becomes high at high switching frequency. In this paper, the method of reduction flat transformer temperature in LLC resonant converter for PDP is proposed by analysis of core loss and experiment. Low-profile power module of profile of about 14mm can be achieved. Temperature of transformer repressed to 71°C.