VARIABLE SWITCHING FREQUENCY ON-OFF CONTROL FOR CLASS E DC-DC CONVERTER

Abstract

The efficiency improvement of the ON-OFF controlled Class E dc-dc converter operated at 20 MHz switching frequency is investigated in this project. It is found that with ON-OFF control, the input power of the converter during the ON mode increases with the increase of the input voltage, and it can be reduced by increasing the switching frequency. With this discovery, a variable switching frequency ON-OFF control is proposed, which slightly increases the switching frequency when the input voltage increases, maintaining the input power during the ON mode slightly higher than the rated output power over the entire input voltage range, and thus highly improving the efficiency of Class E dc-dc converter at high input voltage. A prototype of 9-V to 18-V input, 10-W Class E dc-dc converter has been fabricated and tested in the lab. The experimental results show that, the proposed variable switching frequency ON-OFF control improves the conversion efficiency of the Class E dc-dc converter by 4% to 10% compared to the constant switching frequency ON-OFF control.

Existing System

In the existing system, a phase modulated control is used for a modified Class E dc-dc converter.

Proposed System

This project analyzes the impacts of the input voltage on the performance of the ON-OFF controlled Class E dc-dc converter, revealing that the efficiency degradation at high input voltage is resulted by the increased input power when the input voltage increases, and increasing the switching frequency is an effective way to reduce the input power during the ON mode. Based on this consideration, a variable switching frequency (VSF) ON-OFF control is proposed to achieve high efficiency over a wide input voltage range. OFF control. It derives the root-mean-square (RMS) values for the input current, rectifier diode current and resonant current, demonstrating that the rise of the input power will lead to increased RMS values during the ON mode, resulting in higher conduction losses. The influence factors of the input power in each switching cycle are carefully examined, and it is found that, the input power during the ON mode increases with the increase of the input voltage, and it can be reduced by increasing the switching frequency. Thus, a VSF ON-OFF control is proposed in Section V, which slightly increases the switching frequency with the increase of the input voltage, such that the input power during the ON mode can be reduced and thus improving the conversion efficiency at high input voltage. The prototype of a 9-V to18-V input, 10-WClass E dc-dc converter is fabricated and tested in the lab, and the experimental results are provided to verify the effectiveness of the proposed VSF ON-OFF control.

Architecture

Main circuit of the Class E dc-dc converter