Abstract: The paper presents a step-up controller that is used in WLED driver system and has two dimming modes:PWM dimming mode and Analog dimming mode.In the circuit,the introduction of large capacitor compensating network and the design of low voltage choose circuit effectively improve the circuit dimming performance.System simulation of the step-up controller is simulated in 0.5μm-BCD process.The simulation results show that:The step-up controller can switch between zero load and rated load in PWM dimming mode,the switching time is less than 12μs;Output voltage is adaptive to the dimming voltages in analog dimming mode,when the load is 6×6,6×8,6×10WLED array,the output stabilizes at 20.4V,27Vand 33.3V,and the LED current is set to 20mA.This design improves the WLED driver dimming performance,and thus enhances the quality of the LCD display.