The drive for energy conservation and power efficiencies is common worldwide today and scientists and academics are at the cutting edge of that drive.

The Hong Kong Polytechnic University's work on generating greater efficiencies in power factor corrected (PFC) switching supplies has been winning major awards and is recognised as an important driver in energy efficiency.

Dr Martin Chow Hoi-lam, along with his colleagues, Professor Lee Yim-shu, Lee Chung-ping and Cheng Yiu-lam at the Power Electronics Research Centre in the University's Department of Electronic and Information Engineering, have found that the overall efficiency of PFC power supplies can be improved by employing non-cascading structures. The team have coined this design approach the "Reduced Redundant Power Processing Principle."

"The conversion of electrical energy from high voltage AC to low voltage DC is convenient but is less than 50 per cent efficient," says Dr Chow. "Our prime objective is to improve efficiency to 70 per cent and, at the same time, lower power loss during transmission."

"This means a compromise between efficiency improvements and achievable input power in terms if circuit complexity and device stress."

The team's study and investigations resulted in a design procedure for highly efficient PFC power supplies. A series of practical circuits were built and entered in Efficiency Challenge, an international design competition for energy efficient ac-dc power supplies, jointly sponsored by the California Energy Commission and the US Environmental Protection Agency.

The team's second entry in this competition also drew accolades. Their AA-battery-charged design was based on On Semiconductor's NC-P1215A variable off-time switch mode power supply controller. The design, with 6.25V output voltage, 2.5W output power and 0.4A output current delivers an active power efficiency of 74 per cent and a no-load power consumption of 0.16W. The judges observed that the Hong Kong Polytechnic University's battery charger had an impressively low parts count and that the device delivered good efficiency for such a low output power.

The competition attracted entries from universities and private sector companies from the United States, Taiwan and Hong Kong. With wins in two separate categories, the Hong Kong Polytechnic University team was awarded the overall Grand Championship (Open Category).

"These competitions are a great opportunity to showcase the work and the innovations we as academics undertake. There is now ever increasing demand at both industry and consumer level for new energy consumption standards in electrical appliances and general power efficiency. We have shown that with our designs we can deliver efficiencies and at reasonable costs," Dr Chow says.



Dr Martin Chow Hoi Lam
Department of Electronic and Information Engineering
The Hong Kong Polytechnic University
enmartin@polyu.edu.hk