A High Efficiency Controller IC for LLC Resonant Converter in 0.35 μm BCD

This paper presents a LLC resonant controller IC for secondary side control without external active devices to achieve low profile and low cost LED back light units. A gate driving transformer is adopted to isolate the primary side and the secondary side instead of an opto-coupler. A new integrated dimming circuitry is proposed to improve the dynamic current control characteristic and the current density of a LED for the brightness modulation of a large screen LCD. A dual-slope clock generator is proposed to overcome the frequency error due to the under shoot in conventional approaches. This chip is fabricated using 0.35 μm BCD technology and the die size is 2×2 mm^2. The frequency range of the clock generator is from 50 kHz to 500 kHz and the range of the dead time is from 50 ns to 2.2 μs. The efficiency of the LED driving circuit is 97 % and the current consumption is 40mA for a 100 kHz operation frequency from a 15 V supply voltage.