High efficiency adaptive boost converter for LED drivers

This paper presents the design and simulation results of an 89% power efficient CMOS adaptive controlled boost (step-up) LED driver implemented in 0.25 μm BCD (Bipolar CMOS DMOS) technology. A novel adaptive minimum frequency control provides up to 32 V from a single battery (3.6 V to 5.5 V) input supply to 10 series-connected LEDs at the output. The proposed control scheme provides an accurate load current (3-50 mA) while achieving 6%-12% higher power efficiency than conventional fixed on-time schemes. The novel control circuitry is able to switch between PWM (Pulse width modulation) and PFM (Pulse frequency modulation) automatically by calculating the feedbacks from the inductor and LED´s currents. This controller is functional from light to heavy loading situations which is critical in improvement of power efficiency and battery life-time for high-boost ratio applications in order as provide accurate LED current.