Franki Ngai Kit Poon

A novel high frequency current-driven synchronous rectifier for low voltage high current applications

A novel current-driven synchronous rectifier is presented in this paper. With the help of a current sensing energy recovery circuit, the proposed current-driven synchronous rectifier can operate at high switching frequency with high efficiency. Compared with those voltage-driven synchronous rectification solutions, this current-driven synchronous rectifier has several outstanding characteristics. It can be easily applied to most switching topologies like an ideal diode. Constant gate drive voltage can be obtained regardless of line and load fluctuation. Converters designed with this synchronous rectifier are also capable of being connected in parallel without taking the risk of reverse power sinking. The principle of operation is given in the paper. A series of experiments verify the analysis and demonstrate the merits.

Current-driven synchronous rectification technique for flyback topology

For low voltage, high current application, synchronous rectification technique can help improve efficiency in a flyback converter. This paper investigates some technical challenges within a synchronous rectification flyback converter. One of the major problems is that the discontinuous current mode (DCM) operation is not achievable with a control-driven or self-driven synchronous rectifier. Continuous current mode operation may introduce excessive RMS current and circulation energy at light load or high line condition. To solve this problem, we propose to use an energy recovery current-driven synchronous rectifier for flyback topology. Analysis and experiments demonstrate the performance of this approach.

Voltage-driven synchronous rectification in forward topology

The self-driven synchronous rectification (SDSR) forward topology is widely used in offline low voltage DC-DC power conversion. The major disadvantage of the SDSR forward topology is the conduction of the SR body diode when transformer reset process is over. SR body diode conduction brings excessive loss due to its high forward drop and poor reverse recovery characteristic. In this paper, a new SR drive mechanism is proposed. This drive method effectively prevents the body diode of SR from conduction with a coupled winding and several low power switches. Theoretical analysis and experimental results are shown. A 250 kHz, 48 V input, 5 V/10 A output low profile DC-DC module is designed to verify the proposed idea. 92.3% efficiency is achieved at full load typical line.

Electro-magnetic interference (EMI) due to non-conducted coupling paths in switching mode converter

A simplified model which takes into account minimum coupling paths (MCP) for a switching mode power converter is presented. A minimum number of coupling capacitors are found which connect between all three terminals of a LISN and nodes of a converter circuit. Simulation that shows both inductive and capacitive coupling mechanisms may contribute substantial noise at the input.

Current driven synchronous rectifier with energy recovery sensor

A new current driven synchronous rectification technology is presented. It is intended for high current and high efficiency applications. The synchronous rectifiers so presented are driven by current source instead of convention voltage source. This solves the problems of limited converter input voltage range and inability to operate in parallel in conventional voltage driven SR technology. The proposed synchronous rectification method is verified by practical converters with high efficiency recorded.