Minimized start-up transient and initial inrush current of boost converter for LED lighting

Soft-start is very important for Boost converters to keep output voltage stable. However, previous methods may cause large initial inrush current, big voltage drop, overshoots and long start-up time. In this paper, the conventional resistor capacitor (RC) soft-start scheme is firstly analyzed, and then a novel soft-start strategy by using a variable ramp-slope with predefined voltage (VRSPV) is proposed to improve the start-up performance of the Boost converters. The VRSPV soft-start circuit is designed and implemented in a voltage mode Boost converter for a 4-channels LED lighting application. The input voltage is 5 V and output voltage is 18 V. Measurement results show that the inrush current of the inductor is limited in 2.2 A and the duration of the start-up process is within 1.7 ms. The output voltage is smoothly and steadily changed without any drop and overshoots during the start-up period. The proposed VRSPV soft-start technique shows good performance and is very suitable for the integration on a chip to save the PCB area and the cost.