Piezo power for notebooks

As notebook computers become thinner and lighter, the bulky power adapters used for line current approach the weight of the notebooks, but smaller and lighter adapters may be on the way, thanks to piezoelectric technology, according to a Penn State electrical engineer.

Transformers are needed to convert mains power to the 13 to 14 VDC used by laptops.

Eventually it is intended to make the device the size of a pen, but that is far away. At present the size can be reduced by three quarters.

The smaller adapters are suitable for any appliance that requires an AC-DC converter and transformer.

Transformers are made from piezoelectric materials by applying a chopped electric voltage to one side of a piezoelectric wafer. This on and off voltage creates a vibration in the material, which is converted to an AC voltage on the other side of the wafer. The increase or decrease in the voltage transformed is dependent on the gap between the electrodes.

Most notebooks require about 15 V at less than 1 A and about 12 W. By manipulating the length and width of the piezoelectric chip, it is possible to convert 115 V to 15. A rectifier then converts the alternating current to direct current.

The original piezoelectric devices were rectangular, but they could not produce sufficient power, so the researchers switched to a circular configuration.

Smaller, less complex piezoelectric devices are already in use as set-up transformers in some laptops to light the monitors which can take 700 V to turn on and 50 to 150 V to continue.

One advantage of piezoelectric adapters is that they do not produce the heat that conventional electromagnetic transformers produce. They operate in the ultrasonic range so humans cannot hear any sound produced and they do not produce electromagnetic interference.

The adapters were developed for the American and Japanese market where the mains voltage is 100 to 125 V at 50 to 60 Hz. Eventually, adapters that convert 220 V and 50 Hz will be developed.