High Efficiency Controller IC for LLC Resonant Converter in 0.35 ㎛ 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 ㎛ BCD technology and the die size is 2×2 ㎟. The frequency range of the clock generator is from 50 ㎑ to 500 ㎑ and the range of the dead time is from 50 ㎱ to 2.2 ㎲. The efficiency of the LED driving circuit is 97 % and the current consumption is 40 ㎃ for a 100 ㎑ operation frequency from a 15 V supply voltage.