8.7 A 92.7% Peak Efficiency 12V-to-60V Input to 1.2V Output Hybrid DC-DC Converter Based on a Series-Parallel-Connected Switched Capacitor

초록

The battery voltage (Vbat) is becoming higher in automotive applications for a higher efficiency power system. Accordingly, an ultra-low voltage-conversion-ratio (VCR) buck converter is in great demand. Previous ultra-low VCR buck converters use flying capacitors (CFs) and power switches between the battery and the inductor, as shown in Fig. 8.7.1 (top-right) [1-6]. In these topologies, CFs reduce the voltage stress applied to switches by dividing the Vbat, which has four major weak points. First, because of the high Vbat, CFs and switches are used as high-voltage (HV) capacitors and LDMOSs, respectively, which are bulky and have larger parasitic components resulting in huge power loss compared to a low-voltage (LV) capacitor and CMOS. If compound semiconductors, such as GaN and SiC, are used, the power loss caused by switches can be reduced [1, 6], however, they are less cost effective than silicon devices. Second, previous converters have a problem of on-duty (D) range. Considering several types of battery and their safety margins in the vehicle, the converter is required to properly operate with a Vbat range from 12V up to 60V. Previous converters can have the D either smaller than 0.1 or larger than 0.9 when they operate at this Vbat range and an output voltage (Vo) of 1.2V, as shown in Fig. 8.7.1 (top-left), which makes the converter vulnerable to noise. Third, previous converters have another challenge for the line transient. In the automotive application, Vbat can abruptly vary because of external conditions, as shown in Fig. 8.7.1 (bottom-left). Since the voltage across each CF (VCF) is proportional to Vbat, an abrupt variation of Vbat results in an abrupt change in VCF. This induces a huge inrush current through the CF or unbalanced inductor currents causing fatal damage to the power switches. Lastly, previous converters suffer from a slow load transient response because the load current (Io) is only provided by the inductor. © 2024 IEEE.