A low cost Self-Driven Synchronous rectification Converter for 20V Portable Instrument

Abstract: This paper presents an optimized and enhanced DC-DC converter design for 20V output for portable instrument application. The proposed design is based on isolated push pull topology switched mode power supply. Self- driven synchronous rectification (SDSR) is introduced in the rectification stage in order to create an improved way of rectifying process. N-Channel and P-Channel MOSFETs are used to simplify the synchronous rectification control circuit. Both MOSFETs offer ultra low On-resistance which can be used to achieve higher efficiency than the conventional converter. This converter operates at high speed switching frequency to gain high power-to-volume ratio. In addition, minimum deadtime is set in the design to ensure high efficiency in input-output power transfer. Passive low pass filter is implemented to produce ripple free output voltage in the design. The finalize topology which is push pull with self-driven synchronous rectification is constructed using simple control circuit but maintains good efficiency in its operation. Experimental results show that the proposed converter reacts very well with the self-driven synchronous rectification method. Input voltage is set at 12V and switching frequency is set at 30 kHz in order to minimize the switching stress and conduction losses. Practical implementation of the converter shows that the converter operates at a maximum efficiency of 84.1% and only produces 50mVp-p ripple output voltage which is considered good for a regulated DC output.

Keywords: Self-driven synchronous rectification, SDSR, SMPS, MOSFETs, deadtime, regulated DC output.