Variable Duty Control in Two-Mode LDC for Soft-Change at the Mode Transient

Two-mode low-voltage dc–dc converter (LDC) has been proposed for high and wide input voltage range in order to overcome the drawbacks of the conventional converters. With two operational modes, the two-mode LDC reduce the voltage stresses on the switches and dc offset current. However, it has large differences of capacitor voltage resulting in voltage spike on the switch at the mode transient. Moreover, the dc offset current has large variation between two modes. In this article, a variable control for two-mode LDC is proposed for changing the operational mode softly. The two mode LDC employing the proposed control is shown to minimize the difference of capacitor voltage and dc offset current over the entire input voltage range. The proposed control is verified by a 350–800 V input and 13.9 V/600 W output laboratory prototype.