The purpose of this paper is to propose a flexible load-dependent digital soft-start control method for dc-dc converters in a 380Vdc system. The soft-start operation is needed to prevent negative effects such as large inrush current and output overshoot to a power supply in the start-up process of dc-dc converters. In the conventional soft-start operation, a dc-dc converter has a very slow start-up to deal with the light load condition. Therefore, it always takes a long time in any load condition to start up a power supply and obtain the desired output. In the proposed soft-start control method, the speed of the start-up process is flexibly controlled depending on the load condition. To obtain the optimal speed for any load condition, the speed of the soft-start is determined from a approximated function of load current, which is estimated from experiment results in advance. The proposed soft-start control method is evaluated both in simulations and experiments. From results, it is confirmed that the proposed method has superior soft-start characteristics compared to the conventional one.

An on-chip soft-start circuit based on a switched-capacitor for DC-DC switching regulator is presented. A ramp-voltage, which is generated by a switched-capacitor, is used to make pulse width slowly increase from zero, in order to eliminate the inrush current and the overshoot voltage during start-up. The post simulation results show that the regulator soft starts well with the proposed soft-start circuit.

This paper proposes a simple control method to improve the ignition behavior of cold cathode fluorescent lamp (CCFL) in digital-dimming control. Due to restriking manipulation in digital-dimming mode, the lamp life of CCFL is reduced substantially. To extend the lamp life, we realize a digital-dimming controller with soft-starting technique (DDC-SST) to reduce the high ignition voltage and to eliminate the ignition current spike. The half-bridge resonant inverter is employed in the presented backlight system. Complete analysis and design considerations are discussed in detail in this paper. Simulation and experimental results are close to the theoretical prediction. The overall efficiency of the system achieved at the rated power is over 91%. The ignition voltage is reduced about 30% without any lamp current spike occurred under digital-dimming operation.