Fujitsu Develops World’s First Gallium-Nitride HEMT for Power Supply (june 15, 2009) — Fujitsu announced the development of a new structure for gallium-nitride (GaN) high electron-mobility transistors (HEMT) that can minimize power loss in power supplies.

HEMTThe new technology blocks the flow of current from power supplies in stand-by mode and produces high-density current when turned on.
It has the potential to cut power consumption of electronic equipment by one-third. If applied to data centers, Fujitsu’s new GaN HEMT would be able to reduce total power consumption by 12%.
Power supplies take the alternating-current (AC) power from a wall outlet and convert it to the stabilized direct-current (DC) power that electronics require. As the AC power from public utilities can be erratic in quality, voltage is first stabilized and then reduced, and finally the voltage is converted to DC.
Circuitry that reduces the voltage uses transistors to quickly switch between a state that passes current, and one that blocks it, using the resulting high-frequency AC power.
While power supplies have typically used silicon transistors, silicon transistors suffer from some power loss, known as “on-state loss” when passing current, as well as considerable power loss when switching between on and off states, known as “switching loss”, such that transistor-related losses account for more than one-third (1/3) of all power loss that occurs in a power supply. This issue has sparked efforts to develop new transistors and circuits with low power loss.
Transistors made of materials with high breakdown-voltages(7) are effective in reducing on-state loss – this is attributable to the fact that transistors made with high breakdown-voltages can be designed with closely spaced electrodes, resulting in lower power loss when passing current.
GaN HEMTs are one type of transistor featuring high breakdown-voltage that has attracted much attention in recent years. GaN HEMTs have less than one-fifth (1/5) the on-state loss of silicon transistors and have excellent high-speed characteristics, so that switching losses are less than 1% of those of silicon transistors.
Fujitsu’s new transistors would enable more compact power supplies. High-speed transistor operation would allow for more compact coils and transformers, which have been particularly difficult to miniaturize in conventional power supplies with low-frequency operation: the size of AC adapters for notebook PCs, for example, could be reduced to one-tenth current sizes.

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