Illinois team’s battery charge design wins first prize in national competition

A team of University of Illinois electrical engineering graduate students won a top prize in the international Efficiency Challenge 2004, a power supply design competition to develop more efficient power supplies for consumer electronics. The Illinois team placed first in the 6 volt 2.5 watt design category for cordless vacuums and AA battery chargers.

Existing commercial battery chargers achieve about 50% efficiency. The Illinois design achieved nearly 70% average efficiency, representing a significant leap in what is possible with power supply efficiency.

“Perpetually plugged-in chargers are like parked SUVs with their motors running,” said electrical engineering graduate student Joseph Mossoba. “They draw about 5 watts of power from the outlet and only 2-3 watts make it to the device being charged. That’s why chargers are so warm—much of the power is lost as heat. Even after the battery is charged and removed, many chargers continue to draw between 1 to 2 watts, still wasted as heat.”

According to Mossoba, the increased efficiency is due to two features: the converter uses micropower logic to achieve very low overhead energy consumption; and the burst-mode control is used to halt switching entirely for light loads. The Illinois design uses conventional techniques, but implemented with care to drastically reduce the power consumed when no load is present. In the automobile analogy, it’s like dispensing fuel to the engine only as needed. So when the car is not moving, the engine almost stops altogether, instead of wasting fuel by idling. Since the Illinois design was entered in the Open Class instead of the Market-Ready Class of the Efficiency Challenge, cost factors were not a priority. Cost reduction techniques that leverage existing processes would enable commercialization.

ON Semiconductor, a global supplier of highly efficient power management solutions, provided technical assistance and parts to university teams competing in the challenge. The Illinois charger design was implemented with various power semiconductor devices from ON.

Chuck Mullett, an electrical engineering graduate from Illinois (BSEE ’60, MSEE ’62) and principal systems engineer at ON Semiconductor, presented the Illinois team with a $2,000 prize at the IEEE Applied Power Electronics Conference in Austin, TX, in March 2005.

“The Illinois entry used state-of-the-art switched-mode technology, popular in today’s power converters,” said Mullett. “It converted the input to high-frequency energy in the range of 60 kilohertz, allowing it to be processed through a miniature transformer and then converted to the required direct current to charge the battery. But, the key to efficient operation at light load was to automatically put the circuit in the ‘burst’ mode to avoid the usual internal losses associated with the high-frequency switching and magnetic losses. The Illinois design also employed extremely low-power logic and analog devices, thus further reducing the power consumed by the charger. I was, again, extremely proud of my alma mater and congratulate Joe Mossoba and the team for their excellence.”

In addition to Mossoba the Illinois team consisted of electrical engineering graduate students Nicholas Benavides, Xin Geng, Grant Pitel, Timothy O’Connell, Surya Musunuri, and Alexis Kwasinski; and faculty members Jonathan Kimball, Philip T Krein, and Patrick Lyle Chapman.