High frequency active-clamp buck converter for low power automotive applications

Low power (5 W-25 W) automotive DC-DC converters have a very wide input voltage range from 4.5V to 42V, and it is usually operated at high switching frequency in order to comply with the strict CISPR-25 Standard for EMI performance. The conventional buck converter is currently employed for such applications owing to its simplicity and low cost, but it has low efficiency at high switching frequencies and high EMI emission due to hard switching. To solve these issues, an active-clamp buck converter is proposed in this paper, which features zero-voltage-switching (ZVS) and hence high efficiency and low EMI emission over a wide input voltage range, making it suitable for low power automotive applications. The operating principles including ZVS mechanism, detailed design considerations and experimental results from a 1 MHz prototype are presented.